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University of Victoria Faculty of Engineering Summer 2010 Work Term Report Vibration Testing Machine: Design, Construction and Analysis Rocky Mountain Bicycles Delta, British Columbia James Herriot V00657090 Work Term 3 Mechanical Engineering [email protected] August 31, 2010 In partial fulfillment of the requirements of the B.Eng. Degree Supervisor's Approval: To be completed by Co-op Employer I approve the release of this report to the University of Victoria for evaluation purposes only. The report is to be considered (select one): NOT CONFIDENTIAL CONFIDENTIAL Signature: Position: Date: Name (print): E-Mail: Fax #:

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Page 1: Report, Vibration Testing Machine-1

University of VictoriaFaculty of Engineering

Summer 2010 Work Term Report

Vibration Testing Machine:Design, Construction and Analysis

Rocky Mountain BicyclesDelta, British Columbia

James HerriotV00657090

Work Term 3Mechanical Engineering

[email protected]

August 31, 2010

In partial fulfillment of the requirements of theB.Eng. Degree

Supervisor's Approval: To be completed by Co-op Employer

I approve the release of this report to the University of Victoria for evaluation purposes only. The report is to be considered (select one):  NOT CONFIDENTIAL  CONFIDENTIAL  Signature: Position: Date:   Name (print): E-Mail: Fax #:  

If a report is deemed CONFIDENTIAL, a non-disclosure form signed by an evaluator will be faxed to the employer. The report will be destroyed following evaluation. If the report is NOT CONFIDENTIAL, it will be returned to the student following evaluation.

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Table of Contents1. SUMMARY:..........................................................................................................................................................3

2. INTRODUCTION:...............................................................................................................................................33. DISCUSSION:.....................................................................................................................................................4

3.1 PRINCIPAL OF OPERATION:................................................................................................................4 3.2 DESIGN CONSIDERATIONS:................................................................................................................6 3.3 CONSTRUCTION AND MACHINING:...................................................................................................8 3.4 TESTING:..............................................................................................................................................10

4. CONCLUSION:..................................................................................................................................................13

5. RECOMMENDATIONS:.................................................................................................................................13

6. References:..........................................................................................................................................................14

List of FiguresFigure 1 Junkers Vibration testing machine....................................................................................5Figure 2 Transverse shear................................................................................................................5Figure 3 Proposed Machine layout..................................................................................................6Figure 4 Graph.................................................................................................................................7Figure 5 Custom anodized aluminum hardware..............................................................................7Figure 6 Bolt holder.........................................................................................................................7Figure 7 Offset shaft and sleeve......................................................................................................8Figure 8 Finalized design.................................................................................................................9Figure 9 Bottom plate with needle bearings..................................................................................10Figure 10 Bolt inserts.....................................................................................................................10Figure 11 Torque specification......................................................................................................11Figure 13 Assembled Dry 1:08......................................................................................................12Figure 12 Wear plate.....................................................................................................................12Figure 14 Assembled with grease ~25 sec.....................................................................................13Figure 15 Completed machine.......................................................................................................14Figure 16........................................................................................................................................14

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1. Summary:This report covers the design and construction of a custom transverse vibration testing

machine. The machine was built for Rocky Mountain Bicycles so that their R&D department

could test various fasteners used in off-road mountain bikes. Severe vibrations during trail rides

can cause the pivot screws to loosen which poses a major safety issue for riders. In order to solve

this problem, different fasteners were considered. Different types of thread locking compounds,

mechanical screw locking devices, and other designs were developed to solve this problem. A

machine which could consistently and predictably test the self loosening characteristics of each

option would be needed. The machine was modeled after the Junkers Testing Machine that was

developed in 60’s. The custom machine has an eccentric main shaft driven by an electric motor.

The eccentric shaft is attached to the top plate and forces the top plate to vibrate on needle

bearings. The offset shaft has an offset center which produces a set vibration amplitude. Since

making the offset shaft would be time consuming, it would be cost prohibitive to make multiple

shafts with different offsets. A double eccentric shaft was made to overcome this issue. This

double eccentric shaft would make it possible to adjust the amplitude of vibration. The machine

was successfully constructed and produced useable results.

2. Introduction:Rocky Mountain Bicycles was established in 1981 and was one of the first companies to

make true off-road mountain bikes. Rocky Mountain continues to push the boundaries of materials and technology and riders have come to expect nothing but the best from their rides. This is why Rocky Mountain focuses so much effort on research and development, all of which takes place in their R&D Facility located in Delta, BC.

During a demo ride of a new full suspension bike one of the test riders noticed several of the pivot screws loosened. This is a common problem on full suspension mountain bikes as they are subject to constant and severe vibration loads when ridden off road. This can pose a serious hazard to the rider and led to discussions in the R&D room about different types of thread locking compounds, mechanical screw locking devices and other designs which could eliminate this problem. It was decided that a method of testing these different thread locking compounds

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and locking devices was necessary for comparison and analysis. A machine which could consistently and predictably test the self loosening characteristics of different types of fasteners would be needed. Web research was conducted which lead to the Junkers transverse shear vibration testing machine. This machine is used by laboratories to test bolted connections for their self loosen characteristics (see Fig 1). The machine works by producing a small amplitude transverse shear movement to the bolted connection. This small shearing action (Fig 2) is enough to loosen an untreated bolt in less than a minute. The machine would have to be heavily modified to suit the needs of R&D. Therefore, a custom Junkers testing machine that could accommodate bicycle parts needed to be designed and constructed.

3. Discussion: 3.1 Principal of operation:

The testing machine was modeled after a Junkers transverse vibration testing machine. The

Junker's transverse vibration-loosening test provides a simplified method for broad scale testing

and inspection of the transverse vibration loosening properties of fasteners. The test machine is

able to generate relative motion in the clamped parts perpendicular to the axis of the fasteners.

The Junkers method provides quantitative results relating the variables of clamp-load, number of

cycles, and amplitude. From Nordic Steels website:

4

Top plate

Figure 1 Junkers Vibration testing machine

Figure 2 Transverse shear

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“A testing machine to compare the relative self loosening characteristics of different bolted connections was developed in 1966 by Gerhard H. Junker. With this machine it is possible to analyze the locking characteristics of fasteners under transverse loading conditions. In this test a bolted shear connection is moved by an eccentric rotating engine. Due to an elastic centerpiece the deformation controlled load is transformed into a mixture of deformation and force. The Junker test is standardized by the German regulation DIN 65151. With the Junker test it is not possible to affirm a secure connection but to compare different connections and safety devices.”[3]

The machine has an eccentric main shaft which is driven by an electric motor. A pair of bearings fit onto the eccentric shaft (Fig3), which transmit the vibrating motion to the top plate. The top plate slides on needle bearings and supports the clamped load of the bolted connection. The top plate vibrates under the head of the fully tightened bolt (Fig 2), requiring the machine to develop considerable force to do so.

As the machine vibrates, the bolt gradually comes undone, losing its clamping effectiveness. This can be seen visually by watching the head of the screw come loose, or by using a force sensor. The force sensor can measure the clamping tension of the bolt and using analysis software, a graph showing the connection coming loose over a period of time can be made. By

5

Offset shaft

Top plateSpring plate

Figure 3 Proposed Machine layout

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comparing the time it takes to loosen a connection, it is possible to gauge the loosening resistance of the fastener.

3.2 Design considerations:

After several discussions with the other members of R&D a set of design criteria was

produced. The machine would have to be able to test different sizes and lengths of screws and

bolts. This is because the hardware used to put together the bikes frames is usually different for

each model, see Fig 5. This proved to be a challenge as the testing machine commonly used is

only designed for one specific length of bolt. To accommodate the different sizes and lengths an

insert would have to be fitted into the machine somehow. It would have to be easy to replace,

easy to duplicate if other sizes were necessary, and fit precisely so that it would not vibrate with

the bolt.

It

was decided that a large

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Figure 4 Graph

Figure 6 Custom anodized aluminum hardware

Figure 5 Bolt holder

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cylindrical insert, held in place by the clamping force of the bolt would be ideal. This would be

easy to make on the shop lathe, using available steel round stock (Fig 6). Another issue that came

up was choosing the amount of eccentricity for the main offset shaft. The offset shaft has an

offset center which produces a set vibration amplitude. It was questioned what the offset should

be, and whether one offset shaft would be enough to test a variety of bolts. Since making the

offset shaft would be time consuming, it would be cost prohibitive to make many of them with

different offsets. The idea of making a double eccentric offset shaft was designed to overcome

this problem. This consists of two parts, the eccentric main shaft and the eccentric sleeve. The

vibration amplitude can be adjusted by rotating the sleeve on the shaft, see Fig 7. The eccentric

shaft has an amplitude rage of 0 to 3mm. There is an extra sleeve which has a bigger offset,

giving a range of 1.5-5mm.

It was also decided that the machine should be able to vibrate an entire bike frame to test the

bolts in place and to see if they loosen in the frame. This necessitated a larger mounting table

with a jig to hold the bike frame in place while it was vibrated. The design was finalized; the

designed machine could perform all the required tasks and could fit a force sensor for later use.

7

SleeveMain shaft

0 mm 3 mm

3 mm 0 mm

Figure 7 Offset shaft and sleeve

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3.3 Construction and Machining:

Construction began with sourcing material and parts. The machine shop has a good

selection of aluminum and steel material, and the machine was designed to use as much material

from the shop wherever possible to save cost and procurement time. The 1.5hp motor, pillow

blocks, and v-belt sheaves were recovered from Rocky’s assembly facility in Saint-Georges,

Quebec. The motor cord had been cut in shipping, necessitating a new extension cord and switch

being wired in. The only material needed was the 1.25” aluminum bar stock for the side plates,

and the steel bar stock for the top and bottom plates. Acquiring this material proved to be

difficult, as most suppliers were out of stock and the one company that promised to ship the

material ended up delaying shipment by 2 weeks. This was not a major problem as many other

projects were on the go as well.

Eventually all the material was ready, and machining could begin. Most of the parts were

made on a manual mill and a manual lathe. The two large side plates and the top and bottom steel

plates were machined on the CNC mill. The bottom plate incorporates rails for the needle

bearings to run in. These rails had to be ground smooth by hand, otherwise the needle bearings

would quickly wear out.

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Figure 8 Finalized design

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The offset shaft proved to be difficult to machine as holding a rotating shaft at a precise

offset while removing material is not easy to do. This required setting up the 4 jaw chuck in the

lathe and setting up the work piece with dial

indicators to get the offset correct. The bolt

inserts required increased accuracy so that

they would fit closely into the bottom plate.

The bolt inserts were done on the lathe to

within .001” then they were polished for a

tight running fit using sandpaper and emery

cloth.

9

Bolt insertBottom plate

Needle bearings

Figure 9 Bottom plate with needle bearings

Figure 10 Bolt inserts

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3.4 Testing: Before testing could begin, a test procedure would have to be made to ensure that each

test was done in a similar fashion. This required the need to make a user guide for the machine,

as well as a testing form. The testing form would be filled out each time a test is completed to

make it easier to gather information. The user guide was made such that a person unfamiliar

with the machine could follow the steps and fill in the test form to produce usable data. The test

consisted of inserting the proper bolt insert and using spacers to position the bolt correctly. Then

placing the bolt insert into the bottom plate and checking the correct spacing. The bolt is

tightened to specification (Fig 11) and the head of the bolt is marked so that angular

measurements can be recorded. The head of the bolt rests on a wear plate. This wear plate is

marked in 15

degree

increments (Fig

12). When the

machine is

turned on the

10

Figure 11 Torque specification

Figure 12 Wear plate

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bolt begins to loosen. As the bolt passes each 15 degree increment the time is recorded on the

test form. This provides a quick means of comparing the loosening resistance of different

fasteners. In the future, using the force sensor in conjunction with the recorded time increments

may provide better results but time constraints prevented this. Once the test form is completely

filled out it is easy to compare the different results, some of these results can be seen in Figs 13-

14

Figure 13 Assembled Dry 1:08

11

Figure 14 Assembled with grease ~25 sec

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It is interesting to note that the greased bolt loosened before the dry bolt. Similar tests

were repeated a number of times to ensure consistency. Red loctite #260 was also tested

and proved to be very effective at resisting loosening. But after the same bolt was undone

and retightened the loctite began to lose effectiveness. Further testing of fasteners with

integrated locking features were scheduled, as well as designing and testing mechanical

locking fasteners in house. Unfortunately time was running out and the work term ended

before these fasteners could be tested.

4. Conclusion:

The Vibration testing machine was designed to specifications set forth by the R&D team. It is

able to test different sizes and lengths of fasteners and can do so in a predictable manner. It was

constructed at minimal cost using available

material. It is able to produce a variable

amplitude transverse shear vibration necessary to

test the fasteners. The machine preformed as

required and testing of different fasteners

produced usable results. A testing form and a

user guide were created to help facilitate testing

in the future.

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Figure 15 Completed machine

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5. Recommendations:

Better results could be obtained using the force sensor in

addition to the timed results. This could produce a graph of bolt

tension versus time and would make more usable data. The

machine currently has bolt inserts for 12mm, 15mm and short

12mm bolts. Additional bolt inserts could be made to

accommodate more sizes of bolts. The spacers used to get the

appropriate spacing in the machine are 5/8 washers, as see in

Fig 16. It may improve the results by using machined spacers

instead. There was only enough time to test several different combinations of screws and thread

locking compounds, additional testing will be needed before the best solution can be found.

6. References:

[1] http://mdmetric.com/nordlock/Nord-Lock%20-%20Junker%20test%20principle.htm

[2] http://www.google.ca/search?q=SELF-LOOSENING+BEHAVIOR+OF+BOLTS+UNDER+TRANSVERSE+VIBRATION&sourceid=ie7&rls=com.microsoft:en-US&ie=utf8&oe=utf8&rlz=1I7GGLL_en&redir_esc=&ei=FJt9TMmhIZC2sAPz_5mDBw

[3] http://www.nordicsteel2009.se/pdf/106.pdf

[4] Criteria for self loosening of fasteners under vibration by GERHARD H. JUNKER* 1972

[5] http://www.boltscience.com/pages/junkertestvideo.htm

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Figure 16

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