Gauges & Gauge design
In mass production, instead of measuring actual dimension of each part, the conformance of the part with tolerance specification, can be checked by gauges.
Gauges are scaleless inspection tools with rigid design, which are used to check the dimensions of manufactured parts.
They do not determine the actual size or dimensions of part.
Used to determine whether the inspected part has been made within the specified limits.
Gauges consist of two sizes corresponding to their maximum and minimum limits.
Also check the form and relative positions of the surface parts. IntroductionFor gauging hole limits plug gauges are used.
For gauging shaft limits snap gauges are used.
May be used by unskilled operators.
No calculations, need not require to find the actual dimensions. Time involved for checking/inspection is considerably reducedNo adjustment is required in their use
Not general purpose instruments. Specially made for some particular component, which is to be produced in sufficiently large quantities.
Give quick results about the conformance or non-conformance of the part with specified tolerances.Plain gauges: Used for checking plain, i.e unthreaded holes and shafts.
1.According to their type: a)Standard gauges b) Limit gauges
2.According to purposes: a)Workshop gauge b)Inspection gauge c)Reference or master gauge
3.According to the form of the tested surface: a)Plug gauge b)Snap,Gap or Ring gauge
4.Accoring to their design: a)Single limit and double limit gauges b)Fixed and adjustable gaugesClassification of Plain Gauge Contd..
1.According to their type :
Standard gaugesmade as an exact copy of opposed(mating) part(b) Limit gauges made to the limits of the dimensions 2.According to their purposes :
Workshop Gauge: To check dimension after manufacture Inspection Gauge: To check part before final acceptance Purchase Inspection Gauge: To check part of other factory Reference or master gauges: To check the dimension of gauge 53.According to the form of the tested surface
Plug gauges for checking holes.
(b) Snap and ring gauges for checking shafts.
Classification of Plain Gauge Contd..SnapRing Based on the standard and limit
(i) Standard gauge (ii) Limit gauge
(b) Based on the consistency in manufacturing process and inspection
(i) Working gauge (ii) Inspection gauge (iii) Reference gauge
(c) According to the shape or purpose for which each is used
(i) Plug (ii) Ring (iii) Snap (iv) Taper (v) Thread (vi) Form (vii) Feeler (viii) Air-gauges Gauges - KEY WORDS
Standard Gauges : These are made to the nominal size of the parts to be tested.
Limit Gauges : These are go and no go gauges.
Plug Gauges : These are used for checking holes of many different shapes and sizes. Ring Gauges : External diameter of cylindrical object.
Taper Gauges : Taper testing gauges. Snap Gauges : These are used for checking outside dimension of a part.
Thread Gauges : These are used for pitch diameter of the thread. Form Gauges : These are used to check the contour of a profile.
Feeler Gauges : For checking the clearance between the mating surfaces. Air Gauge : To measure inside characteristics of a hole using air. Standard gauges: If a gauge is made as an exact copy of the mating part of the component to be checked, it is called as standard gauge.
It has limited applications.
Limit Gauges: Widely used in Industries.
As there are two permissible limits of the dimension of a part, high and low, two gauges are needed to check each dimension of the part, one corresponding to the low limit of size and other to the high limit of size of that dimension.
These are known as GO and NO-GO gauges.
The difference between the sizes of these two gauges is equal to the tolerance on the workpiece.
11Cylindrical Plug Gauges
12Taper Plug GaugesUsed to check size of hole and taper accuracyMade with standard or special tapersSome have "go" and "no-go" rings scribedgauge fits into hole between two rings means within required tolerance
Taper Plug and Ring Gauges1213Thread Plug GaugesUsed for checking internal threads of the "go" and "no-go" varietyBased on same principle as cylindrical plug gauges"go" end (longer end)Should be turned in flush to bottom of hole"no-go" endShould just start into hole and become snug before third thread enters
1314Plain Ring GaugesUsed to check outside diameter of piecesGround and lapped internally to desired sizeSize stamped on side of gaugeOutside diameter knurled and "no-go" end identified by annular groove on knurled surfacePrecautions and procedures similar to those outlined for a plug gauge
1415Thread Ring Gauges
1516Snap GaugesOne of most common types of comparative measuring instrumentsFaster to use than micrometersHave C-shaped frame with adjustable gauging anvils or rolls set to "go" and "no-go" limits of the partSeveral stylesA correctly machined part will pass the first set of jaws and stop at the second end of test. In this manner a part may be checked in one action, unlike the plug gauge that needs to be used twice and flipped to access the second gauge1617Snap Gauges Contd..
17 FEELER GAUGEA feeler gauge (also known as a thickness gauge) is an accurately manufactured strip of metal that is used to determine the gap or clearance between two components.
FEELER GAUGE Contd..
A feeler gauge can be used to check the following:Piston ring gapPiston ring side clearanceConnecting rod side clearance
Radius GaugeA radius gauge is a tool used to measure the radius of an object.
Thread Pitch gauges or screw pitch gauges Metric, ACME, WhitworthGo gauges check the Maximum Metal Limit(MML) and NO-GO gauges check the Minimum Metal Limit(LML).HOLE: MML is LL of hole and hence GO gauge for LL and NO-GO for HL
SHAFT: MML is HL and hence GO gauge for HL of size and NO-GO for LL of size.Part is good , if GO gauge passes through and NO-GO gauge fails to pass.
If both fail to pass, it indicates that hole is under size or shaft is over size.
If both gauges pass, it means that hole is over size or the shaft is under size.Principles Limit Plug Gauges: For checking holes.
GO Size of LL of holeNO-GO Size of HL of hole
Plug gauges are marked with the following on their handles for their identification:
1.Nominal size2.Class of tolerance 3.Go on Go side 4.No-Go on No-go side 5.The actual value of the tolerance 6.Manufacturers trade mark 7. A red colour band near the Not-Go end to distinguish from Go end.23Snap, Gap or Ring gauges: For checking the shafts
GOSize corresponding to HL of the shaftNO-GOSize corresponds to LL of shaft
Adjustable type gap gauges , gauging anvils are adjustable endwise in the horse- shoe frame. Thus a small change within about 0.002 mm can be made in the size range.
Fixed gauges are less expensive initially, but they do not permit adjustment to compensate for wear.
Adjustable gauges are expensive but they permit adjustment to compensate for wear and can also be used over a small range of different setting.
Materials: Good quality high carbon steel. Heat treatment will give hardness and stability. Relatively inexpensive, can be readily machined and brought to a high degree of accuracy and surface finish.241.Go gauges should be designed to check the Maximum Metal Limit, while the NO-GO gauges should be designed to check the Minimum Metal Limit
Snap gauges to check shafts:
GO snap gauge corresponds to HL of shaft, NO-GO snap gauge corresponds to LL of shaft.
Plug gauges to check holes:
Size of GO plug gauge should correspond to the LL of hole , while that of NO-GO plug gauge corresponds to the HL of hole.
Taylors Principle of gauge designIn 1905, William Taylor explained the two processes of checking the component. His concepts, known as Taylor's principles, are used in the design of smooth limit gauges.2.GO gauges should check all the related dimensions (roundness, size, location etc) simultaneously, where as NO-GO gauge should check only one element of the dimension at a time.
According to this rule, GO plug gauge should have a full circular section and be full length of the hole it has to check. This ensures that any lack of straightness, or roundness of the hole will prevent the entry of full length GO plug gauge.
If this condition is not fulfilled, the inspection of the part with the gauge may give wrong results.Gauge tolerance(Manufacturing tolerance)
In practice, gauges cannot be manufactured to exact sizes. The closer the limits are held, the more expensive the gauge is. Some allowance must be provided to gauge maker for manufacturing gauges. This is known as gauge makers tolerance or Gauge tolerance.
Logically, the gauge tolerance should be kept as small as possible, this will increase the cost of manufacturing gauges. There is no universally accepted policy for the amount of gauge tolerance.
Limit gauges are usually provided with a gauge tolerance of 10% of work tolerance.
Tolerance on inspection gauges is 5% of work tolerance.
Tolerance on reference or master gauges:10% of gauge tolerance.Disposition(allocation) of Gauge toleranceAfter the magnitude of gauge tolerance is determined, it must be positioned relative to the work limits so that it does not cause the gauge to accept defective work.
The gauge tolerance zone lies entirely within the work tolerance zone. Due to this, the work tolerance zone becomes small by th