Vibration Testing Machine Design and Build

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
herriotj@gmail.com
August 31, 2010
In partial fulfillment of the requirements of the
B.Eng. Degree
Supervisor's Approval: To be completed by Co-op Employer
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Vibration Testing Machine
Table of Contents
List of Figures
FIGURE 1 JUNKERS VIBRATION TESTING MACHINE...................................................................................4
FIGURE 2 TRANSVERSE SHEAR...........................................................................................................................4
FIGURE 3 PROPOSED MACHINE LAYOUT........................................................................................................5
FIGURE 4 GRAPH.......................................................................................................................................................6
FIGURE 5 BOLT HOLDER........................................................................................................................................7
FIGURE 6 CUSTOM ANODIZED ALUMINUM HARDWARE...........................................................................7
FIGURE 7 OFFSET SHAFT AND SLEEVE.............................................................................................................7
FIGURE 8 FINALIZED DESIGN...............................................................................................................................8
FIGURE 9 BOTTOM PLATE WITH NEEDLE BEARINGS.................................................................................9
FIGURE 10 BOLT INSERTS....................................................................................................................................10
FIGURE 11 TORQUE SPECIFICATION...............................................................................................................10
FIGURE 12 WEAR PLATE......................................................................................................................................11
FIGURE 13 ASSEMBLED DRY 1:08......................................................................................................................12
FIGURE 14 ASSEMBLED WITH GREASE ~25 SEC...........................................................................................12
FIGURE 15 COMPLETED MACHINE...................................................................................................................13
FIGURE 16..................................................................................................................................................................14
2

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
3

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
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:
4
Top plate
Figure 1 Junkers Vibration testing
machine
Figure 2 Transverse shear

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:
“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.
5
Offset shaft
Top plate
Spring plate
Figure 3 Proposed Machine layout

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
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.
6
Figure 4 Graph

It
was decided that a large
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.
7
Sleeve
Main shaft
Figure 6 Custom anodized aluminum hardware
Figure 5 Bolt holder
Figure 7 Offset shaft and sleeve

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.
 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
8
0 mm
3 mm
3 mm 0 mm
Figure 8 Finalized design

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.
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

 3.4 Testing:
Before testing could begin, a test procedure would have to be made to ensure that each
test
was
done
in a
10
Figure 10 Bolt inserts
Figure 11 Torque specification

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 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
11
Figure 12 Wear plate

Figure 13 Assembled Dry 1:08
12
Figure 14 Assembled with grease ~25 sec

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.
13
Figure 15 Completed machine

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=ie
7&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
14
Figure 16

[4] Criteria for self loosening of fasteners under vibration by GERHARD H. JUNKER* 1972
[5] http://www.boltscience.com/pages/junkertestvideo.htm
15

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