The Handbook

Production, use and maintenance of wood bandsaw blades

A M A N U A L F R O M S A N D V I K S T E E L

Introduction

A. Forests of the earthHarvesting and wood production - Cost structure

B. Wood bandsaw steelResearch and development - Characteristics of wood bandsaw steel - The Sandvik Multishift Concept - Future trends

C. EconomyThe sawmill cost structure - The three-leg philosophy

D. BandsawingAdvantages of bandsawing - Types of bandsaw - Operation of the bandsaw

E. Choosing bladeBlade parameters - Tooth shapes - Hook angle - Clearance angle - Pitch

F. WorkshopSafety - Storage and transport - Machines and equipment

G. ToothingPunching - Laser cutting - Water-jet cutting - Cut to length

H. WeldingMIG welding - TIG welding - Flash-butt welding - Gas welding

Contents

I. Bench workThe bench - Levelling - Tensioning - Straightening - Other tensioning methods

K. Saw settingSpring setting - Swage setting - Guide for amount of set

L. Stellite tippingStellite for wood bandsaw blades - Tipping methods - Annealing - Grinding - Side grinding

M. GrindingThe grinding machine - The grinding wheel - CBN wheels - The cutting fluid - The grinding operation

N. Gullet treatmentFriction martensite - Deburring

O. Inspection of bladesCleaning and inspection - Gullets - Tooth points - Blade body - Tension - Tooth symmetry

P. The Sandvik Multishift™ ConceptThe steel base - The teeth - The treatment - Economy - Blade reliability - Blade calculations - Production, use and maintenance

R. Sandvik Multishift™ Saver – thin-kerf sawingThin-kerf sawing - More finished material - Applications

S. Inspection checklistDo's and don'ts - Follow up

The Handbook• Efficiency in terms of longer operational times or higher feed speeds. • Better utilisation of raw materials. • Safe and reliable production.

Three vital issues that are equally important to the overall productivityof our wood bandsaw blade operation. They form the base for our devel-opment of steel grades, and new and improved products in bandsawing.They play an important role in the co-operation with our customers andpartners in the business, to improve the economy of sawmills worldwide, now and in the future.

The continuous development has to include considerations about ourforest resources, to meet environmental and other needs in our society.

In The Handbook we cover production, use and maintenance of woodbandsaw blades. The detailed descriptions comprise technical informat-ion as well as practical hints on how to make better use of bandsaw blad-es and machines.

To producers of wood bandsaw blades, manufacturers of sawn productsand the management of sawmills, we believe The Handbook could be ofhelp in more ways than one.

We hope you will find it useful!

Sandvik Steel

The Handbook is the property of Sandvik AB.Excerpts, reprints or copies of the contents may be made

with our permission.

Harvesting and wood production

Cost structure

Certification and the environment

Forests of the earth

A

A 2 Forests of the earth

Forests of theearthHarvesting and woodproductionIn very approximate figures the world logtimber harvest amounts to some 3.5 billionm3 a year. Of this a little less than 50% con-sists of industrial wood, whereas the balanceis fuel wood. The major producers are NorthAmerica, Asia including China and Japan,and Western Europe, which together supplyover 70% of the world demand.

Although no significant increase in the worldproduction of timber is foreseen in the nearfuture, it is estimated that fast-growing plantations will play an important future rolefor the wood harvest.

The production of sawn wood is less than 500million m3, where softwood accounts for75%. The largest producing markets areNorth America and Western Europe includ-ing Scandinavia.

The forecast for demand of sawn wood pro-ducts is stable and increasing very little.Globally, wood substitute products have notsignificantly affected the wood market and itis likely that sawn wood will remain firstchoice for wood products for some time tocome.

Cost structureThe more developed a market, the higher isthe demand for advanced sawing technology.The price of logs is by far the most importantfactor influencing the competitiveness of thesawmill industry. This, in combination withhigh personnel costs, makes it vital to make

efficient use of the available resources. It isalso a fact that high production costs ingeneral appear in those areas where log costsare the highest.

Certification and theenvironmentWe have a responsibility to make sure thatforest resources are well managed to meetsocial, economic, ecological and other needsin our society, for the present as well as forfuture generations. In this context, the ForestStewardship Council (FSC) has endeavouredto bring about a measure of control of the earth's forests. The FSC is an internationalbody which gives accreditation to organisa-tions whose job it is to certify companies inthe industry for:

• the standards of forest management• the products made from the wood from

these forests

Certification is an important means to safe-guard our forests and to see to it that the rawmaterial is handled in an economic and effi-cient way, and where serious consideration isalways taken to the environmental aspects.The growing public awareness of forest de-struction and degradation has resulted inincreasing demands that purchases of woodproducts help secure forest resources for thefuture.

Wood bandsaw steel from Sandvik

Characteristics of wood bandsaw steel

The Sandvik Multishift™ Concept

– a case in point

Future trends

Wood bandsawsteel

B

B 2 Wood bandsaw steel

Wood bandsaw steelThe Sandvik Group is firmly committed toresearch. In the special steel sector we availourselves of one of the most sophisticatedresearch centres in the world, in Sandviken,Sweden.

For well over a century we have been produc-ing special steels for very exacting applica-tions. Today the product range covers tube,strip, wire and bar, mainly in stainless steeland in titanium, nickel and zirconium alloys.Our operation focuses on niches in which wehold a leading position in the world market.

Research and development as well as themanufacture of all special steel products, iscarried out with full control of the entire pro-duction chain. With a complete steel works atour disposal we supervise quality from thebeginning to the end, from the melt to thefinished product.

This integration is pursued also in the woodbandsaw steel sector, where we operate oneof Europe's largest bandsaw manufacturingplants at our fully-owned subsidiary inFinland.

Wood bandsaw steelfrom SandvikSandvik Steel is a leading supplier of woodbandsaw steel and bandsaw blades to thesawmill industry. Based on well over a cent-ury of experience, we have concentrated onspecial quality steels and tools to increase theproductivity of our customers.

Our R&D efforts concentrate on developingnew materials for bandsaws and improvingthe properties of existing materials. There isan ongoing investigation of manufacturingprocesses to make sure quality levels are keptalso for future applications.

The premises for wood bandsaw blade manu-facture in Finland give us the unique possibi-lities needed to develop products for use intough surroundings. The factory forms asolid base for the very close co-operationwith our partners in the business, where end-users and machine manufacturers are veryimportant for the contribution of ideas andimprovements. Here, tests and other relatedactivities in development of new materials,new techniques and other sawing parameters,can be carried out in full. The productionfacility is also an important foundation for allthe development work which is the basis ofour international business operation.

Detailed calculations help produce the steel bestsuited for the purpose.

From melt to finished product. Full supervision ofthe steel from beginning to end.

Wood bandsaw steel B 3

Characteristics of wood bandsaw steel It is important that the characteristics of thebandsaw steel well match other factors vitalto the sawing operation. Here are some of thefeatures to which we attach special importan-ce and which, taken together, will producemaximum results.

• mechanical properties combining high strength and toughness

• high purity• excellent flatness• excellent straightness• close tolerances• good weldability• material suited for stellite tipping

Sandvik's wood bandsaw steels are available ina wide standard range for delivery from stock(complete information is contained in ourbrochure S-335-ENG).

One of Europe's largest manufacturing units for wood bandsaw blades is situated at Sandvik's subsidiarynear Helsinki in Finland.

Wood bandsaw blades ready for delivery from theFinnish factory.

B 4 Wood bandsaw steel

The Sandvik Multishift™

Concept is a case in pointThis is a very good example where manyinterests were combined to produce a newproduct with maximum properties. The spec-ial properties of the steel were matchedagainst its further processing and refinementand a heavy emphasis was put on its function.

This produced a concept rather than a band-saw blade and the results have been verypositive. Increased productivity in terms oflonger operational times, higher feed speeds,less need for maintenance as well as improv-ed operational reliability, has given the saw-mill industry another first.

Future trendsDevelopment is an ongoing process. TheSandvik Multishift Concept is followed bythe Multishift Saver Concept, where thinnersawblades are engaged in the manufacturingsequence. This results in more finished sawngoods from the same amount of raw material.The Multishift Saver concept has been tho-roughly tested and investigated where a num-ber of different parameters are concerned,such as tooth shapes, strain forces, cuttingspeed etc.

The close co-operation with manufacturersand endusers will eventually produce newachievements in fields such as higher feedspeeds in bandsaws, to make the sawing pro-cess even more productive and economical.

The Sandvik Multishift and Multishift SaverConcepts are outlined in more detail in speci-al sections in this handbook.

The features of the Sandvik Multishift Conceptwill help sawmills to better yields.

The sawmill cost structure

The three-leg philosophy

Economy

C

C 2 Economy

EconomyThe sawmill cost structureA number of factors influence the sawingoperation. Therefore the cost structure in asawmill is of vital importance in decidinghow to reach maximum production output.Raw material, manpower, fixed assets andother costs make up the bulk of these expens-es. The cost of the tool, in this case the saw-blade including maintenance, is indeed a veryminor investment or only about one percentof the total cost!

We would like to show you how you can geta lot more out of your operation by applyinga quality tool.

This is a picture of the traditional spread ofcosts in a normal sawmill. The upper bar ofthe diagram shows that raw material or logs,amounts to 70%, manpower to 15%, fixedassets to 10% and other costs to 4%. You willalso note that the tool cost is calculated at onepercent of the total expense.

The cost of the tool in a sawmill amounts to about1% of the total.

Savings in applying a high-quality tool willamount to more than the tool cost.

1% 70% 15% 10% 4%

The lower bar shows what is possible to saveon costs, if you invest in a high-quality tool;you will find that the savings add up to con-siderably more than your investment in thesawblade itself!

The chapter on Sandvik Multishift will giveyou more figures about cost savings andcomparisons between different sawblades.

The three-leg philosophyA quality tool will improve the overall pro-ductivity. It affects three important factors inthe sawmilling industry: utilisation of rawmaterial, operational reliability and efficiency.

Correctly applied, the tool will influence thesawmilling operation through:

• better utilisation of raw materials- higher yields- better sawing accuracy- better surface finish

• improved efficiency- longer operational times- higher feed speed- less maintenance

• improved operational reliability- less downtime

The individual sawmill decides where itsstrongpoints are and how best to choose themost economical way to improve productivi-ty. Where one sawmill may prefer to improveits efficiency, another might concentrate itsefforts on better utilisation of raw materials.Operational reliability, however, is by far themost important factor.

Whatever the preference it is vital that theefforts are well planned. Optimum results areonly possible if all three factors outlinedabove can be combined in a perfect match.

The illustration shows, basically, how thevarious legs influence the overall productivi-ty. In the chapters on Sandvik Multishift andSandvik Multishift Saver we have furtheroutlined how varying parameters could influ-ence the productivity.

Economy C 3

The three-leg philosophy in practice.

Utilisation of raw material

Operational relibility Efficiency

Advantages

Types of bandsaw

Operation of the bandsaw

The wheels

The blade guides

Strain

Cutting speed

Feed rate

Lubrication and cleaning

Bandsawing

D

D 2 Bandsawing

BandsawingBandsawing is an economic way of splittinglogs. The major advantage compared to othermethods is that sawing is carried out withthin blades which give narrower kerfs andproduce more boards.

Modern bandsawing is a rapid and flexiblemethod for efficient production. In combination with good sawing economy,bandsawing is turning into an increasinglyinteresting alternative also in areas whereother techniques dominate the woodworkingindustry today.

Not least has the compact design of modernbandsaws opened up the possibilities for efficient production lines where space is limited, also giving better yields and improved overall economy in the sawing operation.

AdvantagesThe modern bandsaw blade operates at ahigh, consistent speed. The angle of the teethremain in the same position during thesawing process and move constantly in thesame direction in relation to the log.

With only a fraction of its entire length engaged in the sawing process at the sametime, the ambient air will cool the blade toeliminate thermal stresses and distortion.

The construction of modern bandsaws makessawing virtually vibration-free which givesthe blade high operational reliability, leadingto better sawing accuracy. The narrow kerfproduces a consistent and very fine surfacefinish and reduces energy consumption.

The development of the bandsawing technique using a thinner kerf in combinationwith sweepsawing, will drastically changethe yield. Tests prove that in using the profiling method with circular saws insteadof the bandsawing technique, some 10%more logs are needed to produce the sameamount of sawn timber.

Stellite tipping combined with high bladestrain is a further advantage which improvesthe sawing result as well as the tool economyof the sawing process.

Types of bandsawLog bandsaws or head saws may be eithervertical or horizontal, arranged as singlemachines or in groups of two or more units.They are primarily used for sawing logs intoblocks or planks.

Band rip saws, mainly employed for processing blocks and planks, are ofteninstalled in groups. To an increasing extentalso planing mills and similar industries aretoday installing band rip saws for the furtherprocessing of their products.

The feed arrangement is often the only feature which distinguishes the log bandsawfrom the band rip saw. When large logs aresawn, the log bandsaw is usually fitted with alog carriage. This method often uses double-cut blades to increase productivity.

The band rip saw is served by feed rollers orchains. This system is normally used alsowhen the log saws are arranged in groups.The technique is most common in Europeand notably in Scandinavia, where log sizesare smaller and the timber is normally pre-sorted.

Bandsawing D 3

Operation of the bandsawThe wheels

Most machines using wide bandsaw bladeshave wheels which are crowned for more sta-ble sawing. The highest point of the crownshould normally come on the forward third ofthe wheel. If the wheels are worn so muchthat their crown changes, the blades will be subjected to an unnecessary stress and maybe damaged. If stellite-tipped blades areused, it is often sufficient that the crown iscloser to the middle of the wheel, as regrinding of these blades does not decreasetheir width.

A log carriage is often used in sawmills wherelarge logs are processed. Bandsaws can be operated vertically and horizontally.

Log bandsaws arranged in groups are often ser-ved by feed rollers or chains.

The modern bandsaw.

D 4 Bandsawing

Check the wheels for crown with the help of a template, supplied by the machine manufacturer, or other available measuringequipment, which shows the original (= correct) crown of the wheels.

The top wheel, and sometimes both wheels,may be tilted backwards or forwards to makethe blade run correctly, with the gullets about5 mm (0.2 in) outside the wheels.

Bandsaw wheels should be ground afterabout 5000 hours of operation. Also checkthe wheel bearings frequently for wear.

The blade guides

The blade guides are steering blocks made ofmetal, hard plastic, hardwood or comparablematerials. They can be one-sided or two-sided, as the case may be. On a vertical bandsaw, one blade guide will be mountedbelow the workpiece and the other above it.In machines where the upper guide is adjustable it should be set as close to the timber as possible to keep the blade undertight control.

On modern bandsaws the upper blade guidecould be controlled so that it can be rapidlyadjusted to the dimensions of each new log.

The highest point of the crown should come onthe forward third of the wheel (exaggerated).

The shape of the wheel may differ, but the result isthe same.

In the correct position the gullets should beapprox. 5 mm outside the wheel during sawing.

One-sided guides press the blade slightly to oneside.

5 mm

Bandsawing D 5

Double-sided blade guides must not be set soclosely as to generate heat in the blade. Makesure their front edges are not worn, since thisresults in poor guiding of the blade, with therisk of crooked sawing and fatigue cracks inthe gullets due to vibration.

One-sided guides butt against the blade andpress it slightly to one side during the sawingoperation. These guides are to be preferred asthey give better support, but they have to bechecked and changed at intervals, as a worn-out blade guide will lead to crooked sawing.

Strain

The strain of the blades is adjusted pneumatically, hydraulically or with counterweights. High strain gives bettersawing accuracy, but it is important that themachine manufacturers´ recommendationsare followed. The normal strain is 100 - 150MPa (14,500 - 22,000 psi), while high strainis 200 - 250 MPa (29,000 - 36,000 psi).

Note: MPa = N/mm2

Cutting speed

The cutting speed is determined by the speedof the wheels. A higher cutting speed willgive a cut with better surface finish andsawing accuracy. It also permits a heavierfeed speed if needed.

The normal cutting speed is 35 - 45 m/sec(115 - 150 ft/sec). A few manufacturers supply machines which will run at cuttingspeeds up to 75 m/sec (245 ft/sec) and withpossibilities to also vary the cutting speed.

When considering what cutting speed tochoose, it is also profitable to be able to varythe speed according to the log dimension tobe sawn and the composition of the wood(frozen timber, hardwood etc.). A variablecutting speed is an important instrument togive optimum sawing result.

One-sided blade guides give better blade support,a worn one will, however, lead to crooked sawing.

Application of strain force.

F

D 6 Bandsawing

Feed rate

In Scandinavia the normal feed rate is about60 - 80 m/min (200 - 260 ft/min). Modernmachine manufacturers, however, have already today developed machines whichoperate at feed rates up to 120 m/min (400ft/min). It is not unlikely that feed rates reaching 150 m/min (500 ft/min) will be possible in the future.

Feeds up to 120 m/min (400 ft/min) areencountered in North America, where heavier machines often operate with thickerblades in softer wood.

Generally speaking it is a good idea to varythe speed of the blade, as outlined above. Therelation between the feed speed and the cutting speed must match perfectly to obtainthe best result.

Lubrication and cleaning

Wheels and blades must be moistened with asuitable lubricant to prevent the accumulationof resinous deposits during the sawing pro-cess and to keep the blade clean. Resin willproduce friction and excess heat which inturn will cause vibrations and lead to crookedsawing and cracks.

Keep the wheels clean by scrapers made ofnon-abrasive material.

Length

Width

Thickness

Tooth shape and pitch

Hook angle

Clearance angle

Variable pitch

Choosing blade

E

ChoosingbladeThere are a few details to think about whenyou choose the blades for your bandsaw. Theessential information required is length,width, thickness, tooth shape with pitch andhook angle. A further important feature is thecapacity of the gullet area which should bematched against feed speed to obtain the bestsawing result.

LengthThe length of the blade is determined by the machine in which it is to be fitted.Recommended blade lengths are supplied bythe machine manufacturers. The actual lengthof the blade is defined as number of teeth andpitch.

WidthThe width of the blade is also determined bythe machine. Maximum width = wheel width+ tooth height + 5 mm (0.2 in). If your facili-ties for tensioning and straightening arelimited or non-existent, a narrower blade willhave to be accepted. Properly maintained, abandsaw blade with swaged teeth can be useddown to about 65% of its initial width,whereas stellite-tipped blades will maintainalmost the same width during their entire life.

ThicknessThe thickness of the blade is determined bythe diameter of the wheels. Blade sizes below1.47 mm (17 BWG) must not be thicker than1/1000 of the wheel diameter, blade sizesabove this thickness must not be thicker than1/1200 of the wheel diameter. In certaincases it is possible to use thinner blades thanthose indicated here, see also the chapter onMultishift Saver sawing.

Theoretically speaking, a thin blade will lastlonger because it is subjected to smallerbending stresses.

E 2 Choosing blade

h

Vf

p

A

Vc

t

Sawing parametersvf = feed speed vc = cutting speedp = pitchh = cutting heightt = feed per tootht = p x υf

υcA = “area” removed by a toothA = t x h

Tooth shape and pitchWhen you choose tooth shape and pitch thereare a few important parameters which shouldbe observed. The most important factors are• type of wood hard or soft wood• cutting height log diameter, block height• cutting speed

When these parameters have been considered,the tooth shape is selected according to • sufficient gullet capacity• adequate side stability• cutting geometry

The most common tooth shapes are designedLS, S and SB.

Choosing blade E 3

The most commonly used tooth shapes.

Tooth shape LS is most widely used forsawing logs and in re-sawing, in both softand hard wood.

Tooth shape S is used for log sawing thanksto its high gullet capacity and relatively goodtooth stability. It is mainly applied in sawinglarge diameter logs.

Tooth shape SB has high side stability and issuited for log sawing, in both soft and hardwood. It is also the tooth shape most com-monly used for sawing frozen logs.

Terminology for bandsaw teeth, α = back angle or clearence angle, β = tooth point angle or sharpnessangle, γ = hook angle, σ = front angle (γ + 90°).

tooth point

tooth height

front

gullet radius

gullet bottom

tooth pitch

gullet

back

α

β

γ σ

Hook angleThe hook angle is selected to give optimumcutting power. A larger hook angle gives alighter and more efficient cut, but at the sametime it reduces tooth stability. For soft woodsand large-size timber you should use 25 - 30°on swaged and stellite-tipped blades and 10 -15° on spring-set blades. For hard woods werecommend 15 - 25° on swaged and stellite-tipped blades and a somewhat smaller angleon spring-set blades.

If the hook angle is too large, the blade willbe pulled sharply against the timber. If thishappens, its forward edge may come too faroutside the wheels. An undersized hookangle requires an unnecessarily high cuttingpower and gives low capacity, it may causevibrations and unstable sawing. In bothcases, the blades are liable to crack, especial-ly in the gullets.

Clearance angleFor Scandinavian conditions, a clearanceangle of 8 - 12° can be used, whereas 12 - 16°is standard in the US.

Variable pitchVariable pitch means that the saw teeth areunevenly spaced in the bandsaw blade. Ablade may have several pitch of teeth, nor-mally 3 - 5 different ones with the same,basic tooth shape. Also different tooth shapeswith different pitch may appear in the samebandsaw blade. Variable-pitch bandsaw bla-des, a feature made possible by modern toot-hing and grinding techniques, are mostwidely used in North America.

One advantage of unevenly spaced teeth isthat they eliminate or dampen the harmonic vibration that causes "washboard" in sawntimber. Feed speeds can be increased as targ-et sizes and kerfs are reduced. This techniqueis claimed to be efficient in sawing frozenwood, which implies that variable-pitchbandsaw blades would work well also in theprocessing of hardwood.

Manufacturing and maintenance of bandsawblades with variable pitch require specialmachines, mainly computer controlled, toachieve high accuracy in blade parameters.

E 4 Choosing blade

Application Tooth shape

Sawmills Large logs Hard wood S, SBSoft wood S

Small logs Hard wood SBSoft wood LS, SB

Frozen logs SBPlaning mills Hard wood LS, SB

Soft wood LS, SBSpecial sawing applications Hard wood LS, SB

Soft wood S, SB

Sandvik's recommended tooth shapes for various sawing applications

Variable-pitch sawblade.

Safety

Storage and transport

Machines

Tools

Size of the workshop

Floor

Walls and roof

Lighting

Ventilation

Workshop

F

F 2 Workshop

WorkshopProper care and continuous maintenance ofyour bandsaw blade is vital to the efficiencyand prosperity of the sawmill operation. Hereare a few tricks to help you in your work.

SafetyAdequate action has to be taken to make suresafety rules are followed and that personal pro-tective equipment is used whenever needed.

Goggles have to be used in all grinding work.In dry grinding of stellite, special protectivemasks should be used to avoid the inhaling ofhazardous particles.

Protective clothing to evade cutting fluids tocome in contact with the skin, is an importantpart of the grinder's personal equipment.

Ear protectors are to be used when it is evi-dent that the sound level is dangerously high.A noise level of 85 dB may already damageyour hearing, and noise levels of 120 - 130 dB, not uncommon in many indust-rial surroundings, will be definitely painful.

Special arrangements must be made to col-lect grinding waste, especially from stellite,as this can be hazardous to your health.

Storage and transportCorrect storage of bandsaw blades is impor-tant. The methods for storing vary, someusers prefer to keep the blades hanging on thewall whereas others place them on the floor.The most important thing, however, is thatenough space is left for the storing to permiteasy and efficient access to the blades.

The most important recommendations to cor-rect storing could be summarised as follows:• Avoid too tight curvature in the blade, the

recommended minimum equals radius 150times the thickness

• Loosen the blade so that it forms a larger loop, if it is to be stored for some consider-able length of time

• Make sure that the joint comes in the part ofthe blade with the least curvature

• Protect the teeth with a plastic cover • Store in a dust-free, dry place

When bandsaw blades are transported, theyshould travel in boxes with proper protectivecover of plastic strips.

MachinesDepending on the size of the operation, anumber of machines are needed. These varywith the work to be carried out; in productionof bandsaw blades different machines areused than for example in the workshop of asawmill.

Machines should be set up in the most prac-tical pattern to follow the production line andmaintenance scheme. Make sure there isenough room between machines, and don'tforget to reserve ample space for intermedia-te storing of the blades.

Follow recommendations for correct storage.

R > 150 x t Joint

Workshop F 3

ToolsAll tools should be stored as practically aspossible with regard to the work on hand.Sensitive instruments such as measuringdevices etc., should be kept protected fromgrinding dust and other particles which mightdamage their functions.

Size of the workshopThe workshop should be so large as to giveample space for the work to be done.Bandsaw blades should be easy to handle bet-ween machines, and other tools should bewithin easy reach. In a sawmill the workshopshould be situated so that access to thesawing machines is fast and simple.

FloorThe floor of the workshop is normally madeof wood or woodlike material to protect theblades from damage when moved from onemachine to the other or when transportingthem to the sawing machines.

Walls and roofProduction as well as repair and maintenanceof bandsaw blades produces high-level noi-ses. Make sure that walls and roof are pro-perly insulated to meet the required thres-holds of hearing.

LightingGood lighting is essential for production of aswell as maintenance work on wood bandsawblades. In North America it is not uncommonthat benchwork stations are very dark, to pro-vide better control of the light gap.

VentilationGood ventilation is required to make sure thatgrinding dust is adequately taken care of.

Plastic strip is used for tooth protection.

Wooden floor will protect blades from damage.

Punching

Punching tools

Tool clearance

Clearance angle

Punching force

The punching press

Laser cutting

Water-jet cutting

Cut to length

Toothing

G

ToothingThere are several methods for toothing band-saw blades. The most common one is punch-ing, but new methods such as laser cuttingand water-jet cutting are used to an increas-ing extent, not least thanks to their flexibility.

PunchingPunching tools

In punching the teeth are blanked with apunch and die. The punching tool can beopen or closed. Open tools are normally usedfor punching small teeth whereas closed toolsare recommended for wide bandsaw blades.

It is important to choose the right tool for thejob. The correct tool parameters have to beselected so as not to damage the steel, neitherin the sawblade nor in the punch. The tablegives a few recommendations what steel gra-des should be used in punch and die.

In punching each tooth shape needs its owntool. It must be precision ground with properclearance to avoid punching burrs and defor-mation. Incorrect clearance may also causeundesired residual stresses which may lead tocracking and bent teeth, resulting in unstablesawing. Remember to resharpen the tools fre-quently, worn tools may damage the bladeand cause cracks.

Tool clearance

The tool clearance, as indicated in the illus-tration, is understood as the perpendiculardistance (S) between the punch and the die. Itshould be about 4% of the strip thickness. Inclosed dies the angular clearance (B) shouldbe approximately 1 - 2˚ and starting about 1 - 2 mm (0.04 - 0.08 in) below the cutting edge.

G 2 Toothing

Open and closed tools (punch and die).

C Cr Mo V W

AISI D2 1.6 12.0 0.80 0.85

AISI M2 0.9 4.0 5.0 1.9 6.5

W.-Nr. 1.3 4.2 5.0 3.1 6.41.3344

Recommended steel grades for punching tools.Hardness HRC 60-63.

Clearance angle

To facilitate punching, the punching toolshould have a clearance angle of 2 - 5˚. Thisreduces the cutting force and the tool wearand, together with the angular clearance inthe die, makes sure that no undesired parti-cles from the punched teeth stick to the tool.

Punching force

The force to be applied in cutting steel can becalculated according to a specific formula.This will help ensure that the press is notoverloaded and that the correct punchingforce is applied.

The punching press

The punching press is fitted with an automa-tic feed mechanism which adjusts to the cor-rect pitch needed. The most commonly usedmachines are eccentric presses. Make surethe press is always stable to avoid vibrations,or it may lead to improper punching andincreased wear on tools.

Toothing G 3

S

B1-2

S

1-2 mm

Tool clearance (S) and angular clearance (B).

Clearance angle in punch.

Length of tooth curvature and thickness.

Punching of teeth.

2-5°

t

L

F = A x Ksk, where

F = punching force in N or lbsA = L x t, whereA = cross-sectional area, in

mm2 or in2

L = length of tooth curvature, in mm or in

t = thickness of blade, in mm or inKsk= shear strength, approx. 80% of

tensile strength in MPa or psi.

G 4 Toothing

Laser cuttingIn a laser system, energy in the form of lightis focused optically to produce a high-densi-ty beam in a small area. Enough energy canbe focused and delivered to a spot on a pieceof material to actually generate heat to meltthrough. The laser cutting process requiresmachine tool platform to support the cuttinghead.

Normally, when cutting teeth to bandsaw bla-des, the cutting head is moving in one direc-tion meanwhile the strip is moved in anotherdirection. The two axles are controlled bycomputers.

The main advantage of laser cutting is itsflexibility. No tools for different tool shapesare needed, the shapes are programmed andeasy to change if need be, all you have to dois to choose a new program. An added bene-fit is the possibility to cut complicated toothshapes, such as variable pitch.

With its high heat density, laser cutting cau-ses a heat-affected zone (HAZ) where thestructure and the hardness of the steel chang-es. The layer of HAZ has a very hard zone ofuntempered martensite, which must beremoved to avoid damages in the steel duringthe sawing operation, when the blade bendsover the wheels.

Laser cutting is applied in manufacturing ofbandsaw blades where many different toothshapes and often complicated ones, are used.

Water-jet cuttingWater-jet cutting is a technique where mate-rials are cut using a jet of water forced froma nozzle at very high speed and pressure. Incutting steel, an abrasive medium is oftenused together with the water when it hits theworkpiece.

The cutting nozzle is normally mounted on asaddle on the cross axis of a twin-motion sys-tem. When cutting bandsaw blades the strip isfed in another direction.

The greatest advantage of water-jet cutting inthe manufacture of bandsaw blades, is theflexibility to cut complex tooth curvaturesand the fact that the steel in the cut zone willbe free from thermal and mechanical stresses.

The cut surfaces are somewhat rough and mustbe ground to eliminate the risk of cracking.

Like in laser cutting this method is suited formanufacturing wide bandsaw blades whichcall for many different and often complicatedtooth shapes.

Cut to lengthThe bandsaw blade is normally cut to lengthafter toothing. When cut, the ends have to beat an angle of exactly 90˚ to the back, to avoidthat the blade twists. The actual length of theblade is defined as number of teeth and pitch.

The steel must be cut at a 90˚ angle against theback edge of the blade.

90° 90°

Toothing G 5

Normally the blade is cut and welded at theback of the tooth, as the welding operationcreates zones where the mechanical proper-ties are lower. In flash-butt welding, wherethe influence is lower, the joint can be madeat the bottom of the tooth, which will givebetter current distribution during welding toproduce a more homogenous joint.

The strip is cut to length with powerful shears. The cutting edges must be sharp toavoid cutting burrs, tearouts and other deformation. If burrs form, they should befiled away to make sure the surface is wellprepared for homogenous welding. In laserand water-jet cutting, toothing and cutting ofthe strip is carried out in the same operation.

Cutting to length is made in powerful shears.

MIG welding

Equipment

Feeding device for wire

Welding gun

Filler metal

MIG-welding machine

TIG welding

Flash-butt welding

Gas welding

Treatment of the weld

Welding

H

H 2 Welding

WeldingWelding is the most common method to joinbandsaw blades. Normally four differentmethods are used:• MIG welding• TIG welding• Flash-butt welding• Gas welding

Welding influences the properties of the stripmaterial in a negative way. During the welding operation the material first melts andthen solidifies very fast. The blade will rapidly carry off the heat and the surroundingmaterial will be heat-treated in this process.The result is a structure in a heat-affectedzone consisting of untempered martensite,pearlite and bainite on the side of the weld.The untempered martensite in the weld isvery brittle as this is a casting structure.

One way to lower the hardness of the steel isto heat the sawblade to approximately 400˚C(750°F) after welding. There is a risk, howe-ver, that cracks may have appeared alreadybefore the annealing. This is the reason whywe recommend annealing to be carried outright after the welding sequence.

A better way is to heat the strip edges to atemperature of 400˚C (750°F) during theentire welding process. The weld does notcool off so fast as to produce e.g. pearlite andbainite in the weld and in the heat-affectedzone. This procedure may well be appliedalso for the repair of cracks, when the bladematerial should be heated until it has reacheda blue-gray shade.

It is important to have good control of annealing times and annealing temperatureso that the weld does neither become toohard, nor too soft.

MIG weldingThe most commonly used method to joinbandsaw blades is by MIG (Metal Inert Gas)welding. It is carried out in a gas-shieldedatmosphere which surrounds an electric arc.In MIG welding an electric arc is struck between a continuously fed, consumablewire electrode and the workpiece, the bandsaw blade, all enclosed by the protectivegas. The electric current to the electrode isproduced via a relay in the welding gun. It isconnected to the plus pole of a continuous-current circuit. The electrode is fed mechanically, melts in the arc and changesinto larger or smaller drops to be deposited atthe welding point. A gas protects the arc, themelt and the filler metal from being affectednegatively by the oxygen and nitrogen in thesurrounding air. It is fed concentrically to thewelding point around the electrode.

Equipment

The main elements of the MIG-welding equipment is the power source and the feed-ing device for the electrode and the welding gun.

MIG welding is carried out almost exclusivelyby direct current and with the electrode attached to the plus pole of the power source.

The MIG welding technique.

Nozzle

Protective gas Wire electrode

Weld metalBase metal

Welding H 3

The most common power source is a rectifier, although sometimes a welding converter is also used. The machine is adapted by controlling the speed of the electrode and the arc current, in this way thecurrent intensity can be controlled to stabilise the arc at the point between the welding gun and the welding point.

Feeding device for wire

The feeding device shall continuously transport the electrode to the arc. The electrode is fed by a wire guide. In relation tothe electrode bobbin and the welding gun, thefeed motor is placed in a position where theelectrode is fed through the wire guide.

Welding gun

The welding gun is the tool by which theelectrode is guided along the joint. Itsupplies the current needed for the electrode,it forms the necessary gas shield and it startsand interrupts the welding sequence.

The electrode, the protective gas as well ascurrent for welding and operation, is fed intothe gun from a special package of tubes.

Filler metal

We recommend as filler metal a wire gradecorresponding to the strip steel (normally0.75% C) or a low-carbon, un-alloyed welding wire such as ESAB OK 12.51.

MIG-welding machine

The standard equipment for MIG welding isnormally constructed for semi-automaticwelding. The method is, however, most suitable for automated welding.

A thermostat-controlled equipment for pre-heating and annealing will eliminate the riskof cracking. The annealing is automatic, it issufficient to leave the sawblade in the machine for 5 to 10 minutes after pre-heatedwelding 400° C (750°F).

The welding wire is fed automatically by thewelding gun. Through this is also fed the gaswhich protects the melt during the weldingprocess. A recommended mix of protectivegas is 80% argon and 20% carbon dioxide.

MIG welding of wood bandsaw blade.

TIG weldingTIG (Tungsten Inert Gas) welding is anothermethod suitable for welding bandsaw blades.Contrary to MIG welding the current is notfed via the welding wire but via a specialtungsten electrode, where argon gas is blownat the welding point to prevent oxidation.This is a faster process than gas welding, andthe heat-affected zone is narrower.

Welding is carried out in one passage. Place afew small pieces of identical blade materialclosest to the edges and let the weld continueinto these. In this way the cracks and melts atthe end of a weld can be avoided and the weldwill be very clean and homogenous.

TIG welding is basically an automated weld-ing method, although it can be carried outmanually as well.

TIG welding of bandsaw blades normallyuses filler metal. We recommend wire of agrade corresponding to the strip steel (nor-mally 0.75% C) or low-carbon, un-alloyedelectrodes such as ESAB OK 12.51.

Flash-butt weldingThis method is mainly used in the productionof new bandsaw blades. In certain cases itmay also be used for repair work.

H 4 Welding

Using small pieces of identical blade materialwill prevent weld defects.

Flash-butt welding.

The TIG welding technique.

Tungsten electrode

Nozzle

Protective gas

Arc

Work-piece

Welding H 5

The carefully cleaned blade ends are broughtinto contact under controlled feed and a low-voltage current with high intensity is passedthrough the weld point. The points of contactmelt until the joining surfaces have been raised to the preset temperature. The bladeends fuse and are then left to cool under pressure while they are annealed at intervalsaccording to pre-set annealing programmes. All processes are automatic.

The hardness of the weld is more homogenous in flash-butt welding as compared to other welding methods, as nofiller metal is used.

The diagram shows the various hardness pro-files in flash-butt and MIG-welding joints.

Gas weldingIn gas welding the required heat is generatedby burning acetylene in oxygen. Gas weldingis a commonly practised method, but its bestapplication is for repairs in small sawmills.

Because of the lower penetration capacity ofgas welding, a gap of up to 1 mm (0.04 in) isgenerally used, or else the band ends arebevelled to 60 - 70°. This applies to weldingby stages from the centre of the band. Whenwelding is done straight across from oneedge to the other, there is no gap at the starting end and the gap at the finishing endis varied to suit the thickness of the blade.

In order to prevent weld defects at the beginning and end of the weld, small piecesof band should be placed against both edgesof the blade where the welding work can bestarted and ended. We recommend that youuse the forehand technique and that you startwelding at the edge of the tooth.

In gas welding the blade is heated to 450°C(840°F) and then kept at that temperature forfive to fifteen minutes to temper the weld.The exact time is determined by the bladethickness.

500

450

400

350

300

250-12 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12-9-10-11

Flash-butt and MIG-welding joints show varying hardness profiles.

Hardness across the weld, HV Flash-butt

Distance from the middle of the weld, mm

MIG

H 6 Welding

Treatment of the weldAfter welding the joint must be ground andpolished. This is carried out in a special grinding table, where the blade is fastened tothe curved "bed".

The joint should be placed on the highestpoint of the table during grinding. Make surethat grinding dust is effectively taken care ofby the dust extractor, which should be placedas near to the grinding location as possible. Use an elastic grinding wheel in grinding thejoint. This is an efficient way to control theremoval of excessive material.

The joint should be ground to be absolutelylevel on both sides of the strip. Make surethat the weld is not thicker than the strip aftergrinding. We recommend that the jointshould be a few hundreds of a millimetre,0.03 - 0.04 mm (0.001 - 0.002 in) thinnerthan the strip itself. Do not forget to grind carefully also the gullet and back of theblade. Finish the operation with the help of arotary polisher, which will give the joint itsfinal, smooth surface.

After welding the joint must be levelled andtensioned. Carry out the rolling in a tensioning bench and make short rolling passes over the weld to make it flat.

Grinding of the weld to make both sides of thestrip absolutely level.

Polishing the weld with a rotary polisher will givethe joint a smooth surface.

The bench

Levelling

Tensioning

Straightening

Other tensioning methods

Bench work

I

I 2 Bench work

Bench workLevelling, straightening and tensioning arethree interconnected operations which haveto be performed alternately when a blade isbeing prepared. To make straightening andtensioning possible, levelling must always beone step ahead.

The benchAll three operations are normally carried outin a tensioning bench, where the strip is rol-led between two symmetric rollers. The con-dition and position of the rollers should bechecked continuously for the best tensioningresult. The rollers must have exactly the sameradius and be correctly centered to achieveuniform rolling.

During the operation the blade is fed by therollers. The sideways position of the blade isadjusted manually. The rolling pressure isadjusted as called for during the operation inquestion, and normally by a shaft and screw.

The rolls must have exactly the same radius andbe correctly centered.

Tensioning bench.

Correct Wrong

Bench work I 3

The bench should be well lit to get a properfeed-back about flatness etc. It is normallyequipped with a light table to facilitate thechecking of the blade's straightness. It shouldfurther have a back light to check the lightgap in the tensioning process.

LevellingIn levelling the blade is rolled to becomeabsolutely flat before the operations to fol-low. After sawing, lumps and bulges mayhave appeared in the blade, which have tolevelled out to ensure good stability and toobtain an optimum sawing result.

Levelling should be carried out in a bench byrolling. In certain cases, such as when thelumps are very small or when rollers are notavailable, levelling could be made by ham-mering.

During the levelling operation several tracksare rolled lengthwise in the blade. The firstrolling passage is made in the middle of theblade, the next two passages on either side ofthe first track and so on.

The rolling result should be checked with astraight rule. The blade should not be rolledcloser than 20 mm (0.8 in) from the edges.

TensioningThe purpose of tensioning is to elongate themiddle of the blade so that when bending theblade, its crosswise profile corresponds to thecrown of the wheel properly over its entirewidth during sawing. The wheels are normal-ly crowned to prevent the blade from wander-ing backwards and forwards.

If the middle of the blade has not beenstretched sufficiently, it will make contactwith the wheels only at the highest point andwill be quite free to move laterally. The toothed edge will then have no stability; theblade will not cut true, and cracks will occureasily.

Rolling of bandsaw blade.

4

6

2

1

3

5

7

20 mm

20 mm

Rolling is made from the centre of the blade out-wards towards the edges.

A blade which makes contact with the highestpoint of the wheel only, will travel laterally.

Compared to the toothline and back edge, thecentre is elongated by rolling.

Tensioning is carried out by rolling severaltracks lengthwise, starting in the middle ofthe blade as in the levelling process. As themiddle of the blade will be stretched morethan the edges, the higher rolling pressure isapplied here, to gradually decrease towardsthe edges (see illustration under Levelling).The rolling pressure should not be too high,as the blades will then become wavy and dif-ficult to level afterwards.

The tension is normally measured by check-ing the light gap with a straight rule. Thelight gap is formed when lifting up the bladefrom the bench. The amount of light varieswith the blade size and the shape of thecrown of the wheels. The table shows theapproximate recommended values in anumber of cases.

A correctly tensioned blade should fit on thewheel as described in the illustration.

If the tensioning is insufficient and the lightgap is not large enough, the blade will be incontact only with the middle of the wheel andresult in unstable sawing. If tensioning is toohard, the light gap will be too large, in whichcase the blade edges will tighten too muchand increase the risk of cracking.

StraighteningThe purpose of straightening is to elongatethe back edge of the blade to make it morestable during the sawing process. When theblade is set up in the machine, the tensionwill be concentrated to the toothline becauseof the curvature of the back edge. This givesthe toothline the rigidity and stability neededto keep the blade from crooked sawing.

I 4 Bench work

Checking the amount of tension.

Correctly tensioned blade on wheel.

Blade width Light gapmm in mm in

100 4 0.3 0.01150 6 0.6 0.02200 8 0.9 0.03250 10 1.4 0.05300 12 1.7 0.07400 16 2.7 0.11

Bench work I 5

When the blade is cutting, it will heat up pri-marily in the teeth and in the region belowthem. This elongates the toothline and has tobe compensated for by straightening the backedge somewhat.

When the blade is sharpened it becomes nar-rower, and the back edge comes closer to themiddle of the wheel. Consequently the tens-ion of the blade tends to move away from thetoothline towards its back edge. This tenden-cy is counteracted by lengthening the backedge of the blade to a corresponding degree.

Straightening is made by a few rolling passesat the back edge of the blade using low rol-ling pressure. Do not roll closer than about 20mm (0.8 in) from the back edge, because theback of the blade is liable to crack if it getsrolled too hard.

The desired curvature will be produced morerapidly the closer to the back edge the pres-sure is applied, or the heavier the pressure onthe rolls. But proceed slowly and check fre-quently.

Automatic levelling,tensioning and straightening machinesIn modern benching machines levelling, ten-sioning and straightening operations are car-ried out automatically.

Contact sensors or no-contact probes measu-re the deviation over the entire length of theblade at selected intervals, and indicate devi-ation in flatness and straightness as well aslumps and bulges which may have appearedin the steel. Based on the measurementresults, the pair of rollers work to correct thedeviations. Measurement and rolling is con-tinued until deviations fall within the chosentolerances.

In machines for automatic tensioning andstraightening, the program measures theactual level of tension over the entire bladewidth. The rolling station is activated, andremains active for so long as it takes to achieve the correct tension level. Tensioningand straightening procedures can be pre-pro-grammed as regards the blade dimension aswell as the required amount of tension andstraightness.

Automatic machines carry out all the func-tions they are programmed for without super-vision and come to a stop on completion ofthe programme. This makes it possible forthe workforce to concentrate on other duties.

To get a good result in benching, whichincorporates the correct programmingschemes for the benching operation, it is vitalthat the steel has correct, narrow toleranceswith regard to its various properties. Themost important of these are flatness, straight-ness, hardness and surface finish.

Straightening the back edge of the blade.

1.5 m

0.4-

0.6

mm

I 6 Bench work

Other tensioning methodsThere are a few other methods used in ten-sioning bandsaw blades, however they arenot widely used. Among those are the use ofgas flames or high-frequency techniques,methods not commonly used but in certaincases still suited for tensioning.

Hammering Hammering is not recommended as it causespoint-formed stresses in the sawblade whichin turn give the blade undesired properties. Itmay result in unstable sawing and increasesthe risk that cracks appear. Where hammer-ing might be the only possible method tochoose, here are a few hints and recommen-dations to get the best result.

Hammer against an anvil with a piece ofleather between anvil and blade, or use awooden base. Together with an intermediatepiece of leather, this will have the same resi-lient effect and makes it easier to press downlumps and bulges.

Hammer as little as possible. If you have to,use a hammer with highly polished andslightly convex faces to avoid marking theblade. Beat out the irregularities with lightbut firm and correctly aimed blows.

Make it a rule never to strike too long at onepoint. Strike a few blows where necessary,check the result and hammer again if called for.

Benching centre.

Spring setting

Swage setting

Saw setting

K

K 2 Saw setting

Saw settingThe object of spring setting, swage setting orstellite tipping is to provide clearance for thesaw in the cut. The aim is to reduce the fric-tion from the sawn timber on the blade, sothat the blade can pass through the kerf with-out excessive heating.

The amount of clearance depends on the natu-re of the timber. The softer and more fibrousthe timber, the greater must be the set of theteeth in order to reduce friction from woodfibres projecting from the newly cut surface.

Soft timbers give coarse, long fibres, where-as close-grained types give hardly any. Thelatter remark also applies to frozen soft-woods, which can be cut with very little seton the saw as the sides of the cut are perfect-ly smooth in this case. Experience has shownthat swage-set teeth, and stellite-tipped all themore so, produce more efficient sawing. Asthe swage-set and stellite-tipped tooth pointshave little opportunity of sideways deflec-tion, they always cut straighter at high ratesof feed than do spring-set teeth.

With spring-set teeth there is a gap betweenone side and the timber, and they naturallytend to follow the line of least resistancewhen under load. This tends to producecrooked cuts, as the teeth are squeezed toget-her and the blade heats up and expands.

The diagram shows how the sawing time hasdeveloped over the years. From sawing timesof approximately two hours with spring-setteeth in the 1950s we manage today to sawfor 15 to 20 hours with stellite-tipped saw-blades in un-interrupted sawing. It should benoted, however, that the techniques in them-selves are not the only reason sawing timeshave increased, a continuous development of

Clearance angle

Side clearance

Correctly set teeth provide enough clearance forthe kerf.

Development of sawing times during the latter half of the 20th century.

1950 19600

5

25

20

15

10

1970 1980 1990 2000

Hours

Spring setting Swaged Stellite

Saw setting K 3

the properties of the steel have a very posi-tive impact on bandsawing. New materials andnew techniques are likely to help increasesawing times considerably also in the future.

In this chapter we concentrate on spring set-ting and swage setting, whereas stellite tip-ping is outlined in a special section.

Spring settingSpring setting is a common method wherenarrow-sized bandsaws are concerned andwhere the quality of the sawn goods is ofminor importance. It is a rather simple meth-od and cheaper than swage setting. Normallyteeth cannot be swaged with a smaller pitchthan 18 - 20 mm (0.7 - 0.8 in).

Spring setting is achieved by bending theteeth aside with a saw set, set pliers or settingmachine. The set should be applied as closeto the points of the teeth as possible, aboutone third of the tooth height, otherwise theteeth can easily be forced back duringsawing.

As a rule the teeth are sprung alternately leftand right. The set of the blade should bechecked after every shift on the saw at thesame time as the teeth are sharpened. A set-ting gauge should be used for measuring theamount of set.

In order to achieve a straighter cut, somesawyers recommend that every second orthird tooth should be straight. The unset teethstay firmly in the middle of the cut and can-not give sideways: this guides the blade.

Swage settingThe main advantages of swage-set teeth ascompared to spring-set ones, can be describ-ed as follows:• longer operational time as the wear

resistance is improved thanks to the higherhardness (cold deformation)

• better sawing accuracy and surface finishthanks to the symmetry

On new blades the teeth should be ground toremove possible defects resulting from thetoothing and to create the proper tooth shapebefore swaging. Take care not to burn thesteel in this process, as it may cause cracksduring the swaging, and check that the teethhave not been bent because of improper punching.

The points of the teeth can be swaged with ahand swaging tool or by machine.

Swaging is done in two stages - upsetting andside dressing.

Spring setting with set pliers.

The tooth is then side-dressed to its finalshape, either by shaping or by grinding. Inshaping, the swaged tooth is pressed into itselevated hardness. Swaging increases thehardness of the tooth point by 7 - 8 HRC.

You can make a deep swage or a swage at thepoint. Deep swaging is done with a heavyswage bar. The advantage of deep swaging isthat the blade can be resharpened severaltimes before it has to be reswaged. Theadvantage of swaging at the point is that thetooth does not rub on the wood to the sameextent as a deep-swaged tooth.

K 4 Saw setting

In the upsetting process the material on theupper front edge of the tooth is pressed backwards and outwards. This is done with aspecially ground swage bar which is rotated.

The swaging anvil must butt against the backof the tooth all the way to the point. Lubricatethe tooth with a wax crayon or with molybdenum disulphide (Molycote).

The swaging process in practice. A = the swage bar, B = the tooth point and C = the anvil.

Location of the swaging anvil.

C

B

A

1 2

3 4

We recommend that the old swage is fullyground off before re-swaging. This willremove the cold-deformed steel from earlierswaging, which is important as excessivecold deformation is likely to result in crackswhen you re-swage.

Improper swaging may be due to the follo-wing:• worn swaging bar, anvil or side-dressing

tool• swaging bar or anvil inaccurately set• incorrect size of swaging bar compared to

strip thickness• assymetric grinding• failure to remove all traces of previous

swage set• friction martensite (burnt steel) due to too

heavy grinding• insufficient lubrication

Note that swage and spring set clearance gra-dually decrease as the blade is resharpened.

Saw setting K 5

Deep swage and swage and at the point. The side clearance angle, A, is determined by the shaping dies.

The two shaping dies or grinding wheels musthave the same setting and angle during swagingor grinding.

Upset tooth point, side-dressed tooth point and finished tooth point.

Guiding figures for the amount of set, valid for spring-set and swage-set teeth:• very soft wood (poplar) 0.5 - 0.7 mm (0.020 - 0.028 in) on each side• soft wood (pine) 0.4 - 0.6 mm (0.016 - 0.024 in) on each side• hard wood (oak, mahogany) 0.3 - 0.5 mm (0.012 - 0.020 in) on each side• frozen or dry softwood 0.3 - 0.5 mm (0.012 - 0.020 in) on each side

A A

Stellite tipping

Stellite for wood bandsaw blades

Tipping methods

Plasma welding

Resistance welding

Manual tipping

Annealing

Grinding

Side grinding

L

L 2 Stellite tipping

Stellite tippingThe operational time of a wood bandsawblade can be increased considerably by tipping the teeth with wear-resistant alloyssuch as stellite. This is especially evident insawing hard woods, but is today also used inthe processing of softer woods like fir andpine.

The stellite-tipped teeth give better surfacefinishes and considerably longer operationaltimes. It is vital, however, that the grindingwork is carried out correctly, preferably byusing wet-grinding machines and suitablegrinding wheels.

To utilise the properties of stellite in full, thebasic steel material for the bandsaw must beof the highest quality to achieve a longer un-interrupted sawing operation.

Stellite for wood bandsaw bladesStellite is an alloy which consists mainly ofcobalt. According to the composition of thealloy there is a number of different stellitegrades with varying mechanical properties.

For sawing wood, the stellite grade No. 12has proved the best solution. It consists of52% cobalt, 30% chromium, 9% wolframand 1.8% carbon, with a hardness of 47 - 51HRC.

Although stellite has a lower hardness thancemented carbide (70 - 80 HRC), stellitegrade No. 12 is very wear resistant, not verybrittle and it can be ground without problems. In some cases stellite grade No. 1is used, a very hard stellite which is preferredfor sawing wood with extremely high siliconcompound contents such as some exoticwood types in Africa and South East Asia.

Stellite tipping of bandsaw blades is todaycarried out almost exclusively by automatedmachines, notably in Europe and NorthAmerica, but manual stellite tipping is stillpreferred in many other parts of the world.

Plasma welding.Stellite tipping gives the tool better wear resistance.

Tipping methodsPlasma welding

Plasma welding is an electric-arc weldingmethod which takes place in controlledatmosphere with high conductivity. An electric-arc is created between two poleswhere the arc functions as the source of heat.

With the help of the electric arc and the plasma-gas flow, a very high energy density iscreated. The high temperature forces the stellite material to melt and makes sure the hea-ting zone, through the density and the strongconcentration, is kept within required limits.

By means of the concentrated electric arcduring stellite-tipping, it is possible to gainfull control of the size of the stellite drop tobe applied and its exact location. Argon isused as protective gas, a gas which is nottoxic, will not burn and which creates verygood arc stability. The gas not only forms theplasma, but will also keep the stellite as wellas the basic material away from the air and aconsequent oxidation.

The stellite is melted and formed in a for-ming tool. This results in a "raw" tooth, withlittle and uniform excess stellite material,creating optimum prerequisites for the subsequent grinding process.

With forming tools it is possible to createvarious tooth shapes with large or small stelli-te tips, thus minimising the consumption ofstellite. The same stellite rod dimension (dia-meter = 3.2 mm, or 0.13 in) can be widelyused but we recommend to use smaller rodsfor smaller stellite-tip dimensions, such as e.g.diameter = 1.6 mm (0.06 in) for strip thick-nesses below 1.0 mm (0.04 in).

To achieve a stellite tip of constant length andthickness, the tooth points should be cutbefore they are stellite-tipped. This cuttingoperation can be carried out in various ways,depending primarily on the needs of the stel-lite-tip shape. It may vary according to toothform and type of saw, as well as the materialto be processed. For this purpose the toothtips are ground out in a grinding machine.

Stellite tipping L 3

Preparation of tooth points for stellite tipping.

Plasma-welded tooth point.

L 4 Stellite tipping

Resistance welding

In this process, contrary to that in plasmawelding, the stellite is applied by means of anelectric resistance process carried out on thebasic material. The melting will only takeplace on the tangent surfaces of the basicmaterial and the stellite respectively. At thesame time the two materials are weldedtogether under low pressure.

With this method the stellite will not meltentirely in the area which is to become thetooth point, the stellite material is thus onlyaffected in the area of contact.In flash-weld operations the following parameters have to be carefully decided withregard to the actual blade quality and thickness (machine manufacturers’recommendations should be followed):• strength of current• flash-weld time• pressure

The adaptation of the stellite dimension tothe thickness of the blade and the size of thetooth is of great importance. Too large differ-ences may cause the basic material and thestellite to melt differently, in which case thebinding between the two materials will not behomogenous.

Depending on the type of stellite-tippingmachine used for this method, the process canbe carried out either by using pre-formed piecesof stellite or pieces cut from a stellite rod. In thelatter case the rod is cut with an approximately1 mm (0.04 in) thick cutting disc.

To achieve the required tooth point geometrya final grinding operation is needed, regard-less of which method is used.

Manual tippingManual stellite-tipping uses ordinary gas welding equipment.

A torch with a flow of 100 litres per hour andusing a 0.9 mm (0.03 in) nozzle, has provedthe best solution. The gas pressure must bevery low. The mixture of oxygen and acetylene must be regulated so that the flameis about three times as long as the white innerpart. The latter should be held in contact withthe tooth-line.

In this operation it is extremely important toachieve the correct temperature in the tooth andalso to obtain stellite drops of the correct size.

If the temperature of the steel is too low, thestellite will not flow out properly, it will forma lump and fail to cover the entire surface ofthe tooth point.

If the temperature is too high, the steel willmelt and the point of the tooth will be ruined.

The teeth can be swaged prior to tipping withstellite to form a small hollow in the front ofeach tooth. The tooth can also be grounddown towards the point to a hook angle ofabout 0˚, the stellite tipping can be appliedwithout swaging.

Resistance-welded tooth point.

Stellite tipping L 5

AnnealingAll stelliting processes, whether carried outmanually with a welding burner or automatically using plasma or resistance welding, call for annealing of the tooth pointsafter stellite-tipping. Due to the carbon contents of the saw steel a re-hardening of thetooth point will occur through the heat influence of the stelliting, developing un-tempered martensite. A part of the tooth pointbehind the stellite tip will become brittle and therisk of breakage will increase. Annealing willlower the high hardness of the steel in the heat-affected zone and minimise the breakage risk.

Annealing can be carried out by differentmethods, using• plasma burner• high-frequency annealing unit• gas flame

Whichever way is used to carry out the annealing, it is important that it is done in areproduceable and controlled way. This isnecessary to be able to apply the same temperature and the same annealing time toeach tooth.

GrindingStellite-tipped bandsaw blades can be groundusing conventional grinding machines, but toachieve better dimensional tolerances andbetter surface finish, wet grinding with CBN(Borazon) wheels is strongly recommended.

Ceramic grinding wheels give a rougher surface finish and the cutting edges lose theirsharpness quickly when rough corners break.

Ceramic grinding wheels could be used inwet grinding when larger stock removal isneeded. More material could then be removed and the surface finish will be better

than that achieved by dry-grinding.To obtain the best precision and surfacefinish with stellite-tipped teeth, wet grindingshould be carried out with CBN grindingwheels. When the teeth are to be reground, itis recommended to only grind the stellite, asCBN grinding wheels may cause frictionmartensite in the gullets.

Tooth gullet treatment with a rotary cemented-carbide deburrer is recommendedto minimise the risk of cracking.

Finished stellite-tipped tooth point.

Precision grinding of stellite.

12

3

L 6 Stellite tipping

Side grindingTo achieve high precision in the teeth theyhave to be side-ground, especially where stellite-tipped bandsaw blades are concerned.In this case the teeth must be side-ground, theoperation may, however, well give better precision also in swaged sawblades. Precisesymmetry in side clearance and in clearanceangles is a pre-requisite for high sawingaccuracy.

The operation is carried out in side-grindingmachines where two grinding wheels, one foreach side of the tooth, work syncronously.They are adjusted to the correct clearanceangles, in the tooth back as well as the toothbreast. Modern machines will grind the sidesof the tooth either on the downwards or theupwards movement of the wheels, or both.

The teeth must be well supported duringgrinding. If there is more molten stellite onone side of the tooth, it has a tendency tobend when ground, due to the asymmetricalside forces. This is also an important reasonwhy the distribution of stellite in stellite tipping must have the correct symmetry.

We recommend to grind in several cycles,instead of one, heavy grinding passage. Sidegrinding of the stellite-tipped teeth should becarried out with CBN wheels, as these willgive better surface finish and accuracy in thetooth tips.

Note:Stellite contains cobalt. As cobalt could be hazardous to your health as well as to the environ-ment, you should take care not to inhale it and make sure it does not get in contact with your skin!

* Stellite is a registered trade mark of Stoody Deloro Stellite Inc.

Precision side grinding.

The grinding machine

The grinding wheel

CBN (Borazon) grinding wheels

The design of the grinding wheel

The cutting fluid

The grinding operation

Grinding

M

GrindingGeneralGrinding is a chipforming machining met-hod. The grinding wheel has a very largenumber of sharp grains which cut chips outof the workpiece in the same way as do othercutting tools.

Two methods dominate in grinding, traditio-nal dry grinding using ceramic wheels andwet grinding, a method which has increasedsignificantly in later years, especially wherestellite is used.

Grinding of bandsaw blades is normally carried out with the help of ceramic grindingwheels or wheels made of CBN, cubic boronnitride. As these wheels are used at high rotation speeds (peripheral speed 30 - 45 m or100 - 150 ft per second), it is vital that selec-tion, setting and maintenance of the grindingequipment is made with the utmost care.

The grinding machineYou should maintain your grinding machinecontinuously, there should be no play in bearings and guides. A vibrating wheel andplay in the feed mechanism can have disastrous effects on the saw teeth. Many oldertypes of grinding machine are often inadequately protected against the entry ofgrinding dust, which in turn causes rapid wearon the moving parts and the surfaces in contactwith them.

In wet-grinding machines it is important thatcooling and lubricating functions are keptclean and that they are working properly inorder to let the fluid jet pass freely to thegrinding point.

The grinding wheelThe denomination of grinding wheels

Grinding wheels are denoted according toISO standards. The marking of the wheelsinclude the following basic elements: abrasi-ve, grain size, hardness, structure and bon-ding agent. The following system is used:

M 2 Grinding

Grinding machine.

Abrasive

A grinding wheel with aluminium oxide isrecommended for bandsaw steel.

Grain size

Wheels of grit 40 - 80 are normally used forgrinding bandsaw blades. We recommend,however, that you use the 50 - 60 range, asfiner-grained wheels remove the metal lessefficiently and are therefore more liable toburn the gullets due to the heavy feed pressure. This in turn may cause gullet cracksand other difficulties during sawing.

Hardness

The hardness of a grinding wheel is indicatedalphabetically. The further on a letter in thealphabet, the harder the wheel it represents.

Use hardnesses L - M - N for grinding band-saw blades. A harder wheel lasts longer, but ismore liable to burn the gullets. On a harderwheel, new, freely cutting particle edges areless easily brought into play as the wheel wearsdown, with the result that it is liable to clog.

CBN (Borazon) grinding wheelsCBN (Borazon) grinding wheels are used toan increasing extent in precision grinding, forbetter accuracy and finer surface finishes atthe cutting edge. CBN wheels are also favou-red thanks to their longer life expectancy and,obviously, their ability to maintain the

grinding profile for a longer period of time.They are used in wet-grinding machines andthey are recommended for grinding of stellite.

It is normally not possible to change theshape of a CBN wheel (ceramic wheels canbe re-shaped to their original form by meansof a special tool). They must therefore beexchanged before their form has changed toomuch, to avoid differences in the shape of thegrinding wheel and the tooth curvature.

Grinding M 3

Worn grinding wheels give incorrect tooth shapes.

Dry grinding.

Structure (normallynot indicated)

BondingagentHardnessGrain size

Abrasive

Norton 38A 60 K - VSSlipNaxos 43A 60 K - VX

Denomination of grinding wheels.

Manufacturer

M 4 Grinding

The design of the grinding wheelThe shape of the grinding wheel and thecombined feed of wheel and blade, mustmatch exactly the profile of the teeth to getthe required tooth shape. This is also important in order to avoid friction martensi-te in various parts of the tooth, and especial-ly so in the tooth gullet.

Keep the wheel well rounded and sharp, thatis, free from any impurities or deposits on thecutting surface. Otherwise the abrasive particles will not cut freely, but will burn thesaw steel.

Certain machines are fitted with a thin, 5 - 10mm (0.2 - 0.4 in) wheel to be used irrespective of pitch. In this case the machineis designed to give the required grindingresults.

The cutting fluidThe cutting fluid has three different tasks. Itshould conduct heat away and it should alsoprevent heat from accumulating. The cuttingfluid thus has a cooling as well as a lubricating effect. In addition to this it shouldalso flush the chips away.

Various types of cutting fluid

Water-soluble fluids consist of water withcertain additives to increase the wettabilityand to protect against corrosion etc. They contain no oil. An emulsion is a cutting fluid consisting ofwater with a mix of 1 to 5% oil. The oil formsdrops of a few thousands of a millimetre insize, spreading evenly in the water. Additivesof sulphur and chloride compounds, willimprove the lubricating effect and facilitatethe forming of chips.

Cutting fluids are most often based on mineral oils.

Wet grinding.

Grinding M 5

How to apply the most suitable cutting fluid

It is important to choose the correct cuttingfluid for the grinding operation. To achievethe best result, however, it is also necessaryto make sure it is applied correctly. The flowmust be large enough, at least one litre aminute per each millimetre of the grindingwheel width, should be choosen. If both thefeed and the speed of the wheel is high, larg-er flows will be needed.

A sufficient flow of cutting fluid is vital. It is,however, equally important that the flow isarranged in such a way that the fluid reachesthe right point. It should be aimed at the contact surface between the workpiece andthe wheel, as this is the point where heat isaccumulated. The design and location of thenozzle is of great significance.

It is also important to clean the cutting fluidin a satisfactory way. The cleaning devicemust be properly maintained. Clean the spacebetween the blasting protection of the grinding wheel and the surrounding machineparts at intervals!

The grinding operationThe feed speed and the grinding speed incombination with the depth of the grinding,must be carefully adjusted to avoid frictionmartensite in the tooth gullets, so called burnt gullets. The grinding feed, as set out in the machine and wheel manufacturers'recommendations, should be followed.

Adjust the shape of the grinding wheel tomatch exactly the form of the tooth curve.Then adjust the depth of grinding to avoidgrinding burrs on the clearance side of thetooth.

After grinding the gullet must have no darkzones. Dark zones indicate that the steel hasbeen overheated. This in turn results in friction martensite, which is extremely hardand brittle and forms a good starting point forgullet cracks when the blade is turned overthe wheel. It is advisable to grind several times, using a small grinding depthinstead of using very hard grinding. To repaircracks would take very long and the timesaved by faster grinding may thus very wellbe lost many times over.

Gullet treatmentTreatment of gullets is discussed in detail ina special chapter, Gullet treatment.

Gullet treatment

N

N 2 Gullet treatment

Gullet treatmentThe most common reason why cracks appearin gullets is that untempered friction marten-site builds up because of too hard grinding.What, then, is friction martensite? It could bedescribed like this:

“Friction martensite is a result of too hardgrinding of the teeth. The friction betweenthe grinding wheel and the saw blade increas-es the temperature drastically in a thin layerof material which is hereby transformed intountempered martensite when it cools in roomtemperature. Friction martensite has a veryhigh hardness and is very brittle, almost likeglass.”

The amount of friction martensite could bedecreased by choosing the right kind ofgrinding wheel and by adjusting the grindingparameters, such as grinding speed, grindingdepth etc. After too hard grinding the resultappears in the tooth gullets in the form ofdeep grinding scratches, grinding burrs anddark zones, as shown in the illustrations.

To minimise the risk of gullet cracking, werecommend that the gullets are polished witha cemented-carbide deburrer. This removescrosswise grinding scratches and grindingburrs, if correctly applied.

The deburrer is operated by a machine at arotation speed of more than 28,000 rpm,which produces adequate chipping withoutburning the steel. Make sure the deburrer isalways kept at the correct angle to polish theentire surface of the gullet bottom.

The two illustrations show the gullet bottomafter ordinary grinding and the same gulletbottom after deburring with a cemented-car-bide deburrer. In the first picture friction mar-tensite can be seen as a white layer on top ofthe rough gullet surface. The martensite isremoved with the deburrer to produce asmooth surface.

Grinding burrs causing cracks and grindingscratches are due to too heavy grinding or use ofthe wrong grinding wheel.

In deburring it is important that the entire surfaceof the gullet bottom is polished.

Gullet treatment N 3

As the highest stresses are concentrated tothe lowest point of the gullet, it is not neces-sary to polish the entire toothline, it will suf-fice to polish the gullet bottom where thecracks normally initiate.

Make sure the deburrer has sharp edges, as adull tool will cause friction between the steeland the deburrer. This, like too hard grinding,will also form friction martensite.

The deburrer should always be kept at a correct angle to produce the best result.

Friction martensite (white layer) is removed witha cemented-carbide deburrer to produce a smoothsurface.

The highest stresses are concentrated to the gulletbottom.

Cleaning and inspection of bandsaw blades

Inspection of blades

O

Inspection of bladesCleaning and inspectionof bandsaw bladesBasic rules to keep your bandsaw blade ingood shape after it has been engaged insawing:

• Clean the blade• Check the following details for possible

damages- gullets - tooth points- blade body

• Check the tension• Check the tooth symmetry

During the sawing process the bandsaw bladewill be subjected to a number of differentstresses which influence the properties of theblade. Also resinous particles will affect itsperformance, and it is therefore importantthat good care and maintenance is observedto get the best sawing result.

When the blade is changed, clean it properlyfrom resin and other dirt particles. Use apiece of cloth and a suitable dissolvent.Brushes or fine abrasive paper could be usedto remove tighter layers. A clean surfacereduces the friction between the blade andthe wheels as well as the blade guides.Cleanliness is also a basic requirement tomake sure the rest of the maintenance opera-tion can produce the desired results.

Inspect the blade after each sawing periodand observe if it has been damaged. Look forgullet cracks, bent teeth, broken tooth points,body cracks etc.

Minor damages can be repaired, while it maynot be economical to attend to larger defects,such as several gullet cracks.

The blade should always maintain its tension.This is seen as a light gap when the blade islifted up. If the light curvature has changed,the blade must be relevelled and retensionedto restore the original light gap. Retensioningis carried out in the same way as when theblade was tensioned during its manufacture.It is often sufficient to make just a few rollingpassages to correct the lost tension.Remember to also check the straightening ofthe back of the blade.

The symmetry of the tooth points should bechecked before grinding. If some teeth pro-trude from the original toothline, they will beground more on one side and on the otherside not at all. This grinding will cause anasymmetrical toothline producing a badsawing result, as well as premature wear ofthe teeth. Check the angles of each tooth tokeep up the desired tooth geometry.

O 2 Inspection of blades

Checking the tooth symmetry.

A unique bandsawing concept

The steel base

The teeth

The treatment

Economy in operation

Comprehensive testing

Efficiency

Higher blade reliability means less maintenance

Calculation of blade costs

Production, use and maintenance

The Sandvik Multishift™ Concept

P

P 2 The Sandvik Multishift™ Concept

The SandvikMultishift™

ConceptA unique bandsawing concept A combination of features make up theSandvik Multishift Concept.

The steel baseThe steel we have developed has a number ofrequired properties.

• Higher tensile strength permits higher blade strain and thus gives better stability in the sawing process.

• Higher relaxation resistance maintains the blade tension longer.

• Higher fatigue strength allows longer operational times.

• Closer dimensional tolerances andbetter flatness ensure advantages inboth sawblade manufacture, sawing performance and maintenance.

The teethWe recommend that the teeth are stellite tip-ped to provide extra high wear resistance.Stellite will increase operational times bet-ween blade changes and means less mainte-nance. The basic Sandvik Multishift stripsteel is, however, also suited for producingswaged sawblades; as it is also harder itincreases the wear resistance and narrowertolerances improve the tooth point symmetry.

Stellite tipping is outlined in a special chap-ter in this handbook.

The treatmentTo get the most out of this unique combina-tion, correct treatment of the teeth is of vitalimportance to make full use of the higherfatigue strength. Correct care and maintenan-ce of your bandsaw blade is a safe and secu-re way to achieve better yields.

Economy in operationIn the Economy chapter we have outlined thespread of costs in the sawmill, showing thatthe cost of the tool makes up about a merepercent of the total cost.

A table showing how to calculate blade costsfor Multishift as compared to standard sawblades, is included at the end of this chapter

Comprehensive testing

Tests under authentic conditions in a numberof sawmills proved that the SandvikMultishift Concept indeed presents someremarkable results in increased productivityand longer operational times.

The tests have been carried out in differentparts of the world and under varying but nor-mal operating conditions for the market inquestion. Due consideration has been takento the type of raw material used, e.g. soft orhard wood, and varying grades of materialcleanliness, as well as to weather conditionsand fluctuations in summer or winter climate, daily operational times etc.

The graph shows that the stellite-tipped standard blade at a certain point in the sawingoperation will start loosing in productivity.This is also where the risk of damage willincrease.

The Sandvik Multishift Concept shows a stable and more productive development. Itsgreater efficiency at the same point in the operational-time curve is mainly due to theimproved characteristics of Sandvik'sMultishift steel, which allows more efficientuse of the overall sawing time.

The Sandvik Multishift™ Concept P 3

1% 70% 15% 10% 4%

Productivity

Operational time

Standard stellite-tipped blade

The Sandvik Multishift Concept

Sandvik Multishift will achieve longer operationaltimes.

Efficiency

By increasing operational times the sawingmill could drastically improve its productivity. Traditionally, breaks are common in connection with blade changes.In applying Sandvik Multishift we createconditions to increase the operational timeand eliminate breaks. The result is higherproductivity.

The illustration shows how efficiency willincrease considerably.

Higher blade reliability means less maintenance

The improved properties of the steel in com-bination with stellite tipping and correct toothtreatment makes it possible to dramaticallyminimise maintenance needs.

In the example we have illustrated what hap-pens when operational time is increased fromfour to eight and sixteen hours respectively.The decreasing need for blade changes andregrindings will result in a subsequent increase in productivity.

Blade utilisation - Sandvik MultishiftCalculation

Number of shifts 2Hours per shift 8Production days per week 5Production weeks per year 48Number of bandsaws 4Blade hours per year 15360

P 4 The Sandvik Multishift™ Concept

Utilisation of raw material

Standard

Multishift Saver

Operational relibility

Efficiency

The three-leg philosophy in practice means overall savings.

Multishift

Sawing time between blade changes Number of blade changes per year

4 hours 3840 8 hours 1920

16 hours 960

The Sandvik Multishift™ Concept P 5

Calculation of blade costs (indexed)Today´s standard Sandvik Multishift Concept Swaged tooth points Stellite-tipped tooth points

Sawing time, hours 4 8 16

Cost of

- new blade 100 (Toothed, welded) 150 (Ready to saw) 150 (Ready to saw)

- grinding (1 round) 5 7,5 7,5

- swaging/tipping 10

- levelling/tension 2,5 3,8 3,8

- blade change 3,5 3,5 3,5

Regrindings after 4 hours 8 hours 16 hours

Regrindings 5 /swage 15 /stellite 10 /stellite

Reswagings/retipping 14 /blade /blade /blade

Grindings

- before reswaging/ 3 times times times

retipping

- after reswaging/ 3 times times times

retipping

Costs

New blade = 100 = 150 = 150

Grinding (rounds) 165 x 5 = 825 15 x 7,5 = 113 10 x 7,5 = 75

Swaging/tipping 15 x 10 = 150 0 x 0 = 0 0 x 0 = 0

Levelling/tension 90 x 2,5 = 225 16 x 3,8 = 61 11 x 3,8 = 42

Blade change 90 x 3,5 = 315 16 x 3,5 = 56 11 x 3,5 = 39

Other costs Deburring Deburring

Total cost 1615 379 305

Maintenance, % 94 60 51

Total sawing time, hours 360 128 176

Blade costs per hour 4,5 3,0 1,7

P 6 The Sandvik MultishiftTM Concept

Proper handling and care of your Multishiftblade will produce the best results. These areour recommendations where production, use

and maintenance is concerned, based on a lotof practical experience and test sawing underdifferent conditions and in various markets.

1. The teeth are blanked out of the steel strip. 2. Grind with aluminium-oxide wheel,adjust shape and remove notches.

3. Stellite tipping. 4. Precision wet grind stellite with CBNwheel. Make sure the gullet bottoms arenot touched by the wheel.

5. Deburr gullet bottoms carefully with acemented-carbide deburrer, ≥28,000 rpm.

6. Inspect the teeth and measure the side cle-arance. The saw is now ready for operation.

Production

Production, use and maintenance

1

1

2

3

2

The Sandvik MultishiftTM Concept P 7

8. Inspect the saw blade. If tooth gullets aredamaged, it is normally sufficient to clean thebottoms with a cemented-carbide deburrer.

9. Inspect the teeth, measure the side clear-ance and symmetry. If at this point the sideclearance is insufficient, the stellite has beenworn down and the blade should be scrapped.

10. Precision sharpen the stellite tips. Wetgrinding with CBN wheel is recommended.Gullet bottoms must not be touched bywheel.

7. After sawing retensionthe blade at intervals asnecessary. Note thatretensioning a Multishiftblade can be differentcompared to a standard-steel blade. The Multishift blade isharder and thereforeneeds higher rollingforce.

7-10. You can repeat the cycle until the stellite has been worn down. If the bladeshows no damage to tips or gullet bottoms,the stellite may normally be reground ten tofifteen times.

Use and maintenance

The higher tensile strip steel permits a higherblade strain. A general recommendation is astrain of 200 - 230 MPa to achieve higher stability and better sawing results. In this

context the maximum capacity of the band-saw is naturally of vital importance. Tomesure the actual blade strain Sandvik hasdeveloped a special strainmeter, availablefrom our Finnish subsidiary.

3

2

1

P 8 The Sandvik MultishiftTM Concept

Note:We want to stress that scrapping of the blade according to our experience will in the end produce the opti-mum economy. Although in some cases there is sufficient steel material to renew the sawblade and perhapsstellite-tip it again, fatigue stresses in the blade and other stresses caused by wear and extended use, will shorten the life of the blade.Tests show that the costs for renewal do not add up to the economical yields achieved by applying a newblade. See also the special chapter on Economy.

Sandvik Multishift™ Saver thin-kerf sawing

A thinner blade increases productivity

More finished material

Applications

A different approach

Loss of blade stability

Loss of tooth stability

Lower gullet capacity

R

R 2 Sandvik Multishift™ Saver - thin-kerf sawing

SandvikMultishift™

Saver thin-kerf sawingA thinner blade increases productivityThe ongoing development of the SandvikMultishift Concept is a continuous process,where the aim is to increase the productivityin sawmills. This is where the MultishiftSaver, a thin-kerf sawing technique, comes in.The Multishift Saver is a thinner sawbladewhich produces a narrower kerf. This narrower kerf would allow more sawn material to be taken out of each log.

The illustration shows what happens in prac-tice when you saw with a thinner blade.

The kerf produced by a normal bandsawblade, will produce a certain amount of boardout of one log. It will also produce an amount of chip and a pile of sawdust.

The thinner sawblade produces a narrowerkerf, which means a larger number of boardswill now be produced from the same log. Itwill, eventually, produce a somewheat largeramount of chip, but a significantly smallerpile of sawdust.

If you look at the cost structure of boards,chip and sawdust respectively, the use of thethinner sawblade will thus have a great influ-ence on the economy of the total sawing operation.

The thinner sawblade produces more boards and more chip, but less sawdust and will improve the econo-my of the sawing operation.

A narrower kerf will produce more board out ofthe log.

Sandvik Multishift™ Saver - thin-kerf sawing R 3

More finished materialApplying a thinner sawblade in the sawingprocess thus produces more board out ofone log. Let's take a look at what happensfurther on in the processing chain as a resultof this.

We assume that the logs are being processedto manufacture boards. First, the board is rip-cut into smaller sections.

They are then cut up into blocks, which inturn will be rip-cut into the final boards.

The comparison shows that considerablymore boards will be produced out of eachblock when we engage the thinner sawbladein the process.

ApplicationsThe main purpose of thin-kerf sawing is to getmore sawn goods out of the raw material. Thisis especially important for planing mills andfor manufacturers of the following products:• parquet floors• solid wood floors• furniture• doors and windows• cupboards, sideboards, wardrobes

and cabinets• panels

Cutting the blocks into boards...

... using a traditional sawblade will produce a certain number of final boards...

... whereas a thinner sawblade will increase theoutput ...

... and raise the productivity.

R 4 Sandvik Multishift™ Saver - thin-kerf sawing

A different approachIn thin-kerf sawing, where a thinner sawbla-de is applied, a number of factors influencethe sawing process and due consideration hasto be taken to varying parameters as compar-ed to sawing with conventional sawblades.

These considerations have been duly notedwhere the Sandvik Multishift Saver is concer-ned. Sandvik has developed computerisedprograms to secure optimum performance inthe blades, they have thus been tailored to suitthe specific application they are intended for.

Here are some of the main issues whichshould be taken into account when a thinnerblade is used.

1. Loss of blade stability

The thinner blade makes it less stable than athicker one. A higher strain force thereforehas to be applied.

Thanks to the improved properties of theMultishift Saver, the strain can, in fact, beincreased even further, which means a considerably higher stability can be achieved.The lower bending stresses which are due tothe blade's reduced thickness, also allows for

higher tensile strain while the total stressesare kept on approximately the same level. Tomeasure the actual blade strain Sandvik hasdeveloped a special strainmeter, availablefrom our Finnish subsidiary.

The graph illustrates the recommended incre-ased strain needed when the thickness of theblade is reduced one step. In the examplestepping down from 1.47 mm (17BWG) to1.25 mm (18BWG) calls for a 10% increasein order to maintain the same blade stability.It should be noted that the information in thegraph is based on the assumption that thestandard or original width of the blade isapproximately 150 times its thickness.

2. Loss of tooth stability

The thinner blade also, naturally, results inloss of tooth stability. Two different possibilities exist to solve this problem.

35

30

25

20

15

10

20 19 18 17 16 15 14

5

00 0.89 1.07 1.25 1.47 1.65 1.83 2.11

Recommended increase of strain when using thinner blades.

Increase of blade strain in %

Blade thickness

mm

BWG

1. Loss of blade stability

⇒ Higher strain force

2. Loss of tooth stability

⇒ Other tooth shape with better side stability or lower tooth

3. Lower gullet capacity

⇒ Higher cutting speed

Sandvik Multishift™ Saver - thin-kerf sawing R 5

To achieve the same stability in the blade,another tooth shape may be chosen. Basedon available tooth data and existing tooth stability, the optimum tooth form for anyapplication will be selected with the help ofcomputerised programming.

The same tooth shape is kept, but the heightof the tooth is slightly lowered. This providesbetter stability to the tooth.

3. Lower gullet capacity

The amount of sawdust in the gullet area hasa strong influence on the sawing operation. Ifthe gullet area is made smaller, this has to becompensated for by allowing less sawdust togather during sawing.

One way to do this is to increase the cuttingspeed of the blade. Relevant tooth data incombination with data on gullet capacity willcalculate the cutting speed versus the feedingspeed and produce an optimum solution. Thehigher cutting speed will thus also give theoptimum amount of sawdust.

Tooth shape A has lower gullet capacity but better side stability.

A =B =

Inspection checklist

S

Cracks in gullet

Maintenance Incorrect grinding, “burnt” tooth gullets GrindingIncorrect swaging, asymmetric swaging Saw settingAsymmetric stellite tipping Stellite tippingIncorrect tension Bench workTooth edge tensioned excessively Bench workBlade too thick for the wheels Choosing blade

Machine Too high blade strain BandsawingToo low blade strain BandsawingWorn wheels BandsawingVibration in bandsaw machine BandsawingWorn blade guides Bandsawing

Sawing Blade clogged with resin, sawdust etc. Inspection of blades

Cracks in body

Maintenance Incorrect tension Bench work

Machine Worn wheels BandsawingBlade guide too tight Bandsawing

Sawing Blade clogged with resin, sawdust etc. Inspection of bladesChips or sawdust between blade and wheels Bandsawing

Blade operates steadily, but runs too far forward, despite reduction of tilt

Maintenance Hook angle too large Choosing bladeBack edge of blade too long Bench work

Machine Worn wheels Bandsawing

S 2 Inspection checklist

Type of fault Cause See chapter

Inspection checklist

Inspection checklist S 3

Blade operates steadily, but runs too far back, despite maximum tilt

Maintenance Tooth edge too long Bench workMachine Incorrect crown profile Bandsawing

Blade guides incorrectly installed Bandsawing

Blade operates unsteadily, blade travels sideways when loading

Maintenance Uneven tension Bench work

Insufficient tension in

relation to crown Bench work

Wrong hook angle Choosing blade

Blade has lost tension Bench work

Machine Wheels not identical Bandsawing

Wheels not parallel Bandsawing

Vibration in bandsaw machine Bandsawing

Too low blade strain Bandsawing

Worn blade guides Bandsawing

Blade operates steadily, but does not saw straight

Maintenance Blade gulleyed Bench work

Teeth have been ground at an angle Grinding

Blade with irregular swaging Saw setting

Incorrect stellite tipping Stellite tipping

Asymmetric side grinding/dressing Grinding

Dull tooth points Grinding

Machine Blade guides incorrectly set Bandsawing

Feed equipment not parallel

with blades Bandsawing

Worn wheels Bandsawing

Worn blade guides Bandsawing

Blade travels rapidly to and fro on the wheels

Maintenance Bad straightening Bench work

Uneven tension Bench work

Blade has lost tension Bench work

Machine Worn wheels Bandsawing

Too low blade strain Bandsawing

Wheels unbalanced, sawdust clogged Bandsawing

Wheels not parallel Bandsawing

Type of fault Cause See chapter

Data and recommendations in The Handbook

may be changed without prior notice.

AB Sandvik Steel, SE-811 81 Sandviken, Sweden.Phone: +46 26-26 38 25 Fax: +46 26-27 23 07

www.steel.sandvik.com

Price 25$.S-336-ENG May 1999