United States Golf Association
PROCEDURE FOR MEASURING
THE FLEXIBILITY OF A
GOLF CLUBHEAD
USGA-TPX3004
Revision 1.0.0
May 1, 2008
1
Change Record
Page
Section
Date
Details
4
6.1.2
3/2005
5
2
6.2.4
1.2
3/2005
5/1/08
2
4.1
5/1/08
9
App. B
5/1/08
Note addressing procedure for determining impact location when
testing irons.
Note addressing alignment procedure when testing higher lofted clubs.
Appendix II, Rule 5a changed to Appendix II Rule 4c(i) to reflect renumbering of Appendix II in the 2008 Rules changes.
Appendix II, Rule 5a changed to Appendix II Rule 4c(i) to reflect renumbering of Appendix II in the 2008 Rules changes.
Appendix detailing test for conformance with Appendix II, Rule 4c(ii)
of the Rules of Golf added.
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United States Golf Association
PROCEDURE FOR MEASURING
THE FLEXIBILITY OF A GOLF CLUBHEAD
1. Scope
1.1 This method covers the procedure for
measuring the flexibility of a golf clubhead
using a pendulum testing apparatus as
administered by the United States Golf
Association (USGA).
1.2 The results of the conformance tests are used
in determining conformity of the club head
to the Rules of Golf, Appendix II, Rule 5a.
1.3 The values stated in imperial units are to be
regarded as standard. The values stated in
SI units are for information only.
2. Applicable Documents
2.1 USGA documents:
Rules of Golf
Technical Description of the Pendulum
Test
Pendulum Test Console
Figure 3.1 - Pendulum Testing Apparatus
4. Significance
3. Summary of Method
4.1 This method uses the characteristic time to
determine the conformity of a golf clubhead
to Appendix II, Rule 5a of the Rules of Golf.
3.1 Using the pendulum testing apparatus;
Figure 3.1, a golf clubhead is impacted
several times by a small steel pendulum. A
characteristic time between the clubhead
and pendulum is recorded for each impact.
The characteristic time is directly related to
the flexibility of the golf clubhead, Ref.
Technical Description of the Pendulum
Test.
The characteristic time of the clubhead shall
not be greater than 239 µs. A maximum test
tolerance of 18 µs is associated with this
test.
4.2 Intermediate screening procedures may be
used to determine clubhead conformance
and increase testing efficiency. However,
the USGA will continue to monitor
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innovations in design and reserve the right
to conduct additional research when
appropriate.
checks to make sure that the device is
performing properly. The computer will
guide the user through the system check.)
4.3 Over time, the procedures outlined in this
document may be changed and the test
tolerance may be reduced as test methods
are refined.
6. Club Preparation and Mounting
6.1 Determination of Impact Location
6.1.1 This test measures the response of a
shafted golf club. If there is no shaft in the
clubhead, one must be temporarily installed
prior to testing.
5. Testing Apparatus Set-up and Preparation
5.1 Connect the ADC/212 digital storage
oscilloscope to the computer and its power
supply. Turn on the computer and launch
the “Pendulum Test Console” by double
clicking the icon.
6.1.2 The normal procedure calls for the
measurement to be made at the face center.
Place the center template on the clubface
and move it from side to side along the
clubface until the heel and toe
measurements at the edges of the face of
the clubhead are equal.
5.2 Remove the pendulum testing apparatus
from the protective shipping container.
5.3 Attach the pendulum tower assembly to the
base assembly using the thumbscrew,
Figure 5.3.
(Note: for irons, the heel and toe
measurement is made at the edges of the
roughened area of the face.)
6.1.3 Repeat step 6.1.2 moving the template up
and down along the clubface until the sole
and crown measurements at the edges of
the face of the clubhead are also equal.
Care should be taken to make sure that the
heel-toe measurements of step 6.1.2 remain
equal during this step.
Tower
6.1.4 With the template situated such that the
heel and toe measurements are equal and
the sole and crown measurements are
equal, mark a circle to indicate the impact
spot for the test. (Note: the heel-toe
measurements do not have to be the same
as the sole-crown measurements, Figure
6.1.)
Base
Figure 5.3 - Pendulum Apparatus, Tower and
Base Assemblies
5.3.1 Attach the data collection cord to Channel
A of the ADC/212 and to the tower at the
connection provided. The test apparatus is
now assembled and ready for the system
check.
5.4
The Pendulum Test Console will
automatically launch a system check. (The
system check is a diagnostic procedure that
4
Raise Pendulum
and
Tighten Spacer
Figure
6.1 – Impact
Template
6.2
Mounting
the ClubLocation
in the Test
Apparatus
6.2.1 Once the impact location has been marked,
place the club in the clamp assembly,
Figure 6.2.1, such that the impact location
is situated in the approximate location of
the ball of the pendulum and loosely secure
the clamp.
Figure 6.2.2 – Pendulum Assembly
6.2.3 With the pendulum assembly out of the
way raise the alignment assembly, Figure
6.2.3, to the approximate height of the
impact location.
Plunger
Figure 6.2.1 – Clamp Assembly
6.2.2 With the club loosely secured, raise the
pendulum assembly, Figure 6.2.2 to its
maximum position and secure.
Figure 6.2.3 – Alignment Assembly
6.2.4 Insert the plunger in the alignment
assembly and gently press it to the club
face. Adjust the clubhead until the plunger
seats squarely on the club face and then
tighten the clamp.
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Note: For higher lofted clubs, a modified
pendulum which includes a rotating tower
assembly is used. The plunger for the
modified pendulum incorporates four pins
rather than two.
Insert the modified
plunger into the alignment assembly and
gently press it to the club face. Adjust the
clubhead and rotate the tower as necessary
until all four pins of the plunger seat
squarely on the club face and then tighten
the clamp and secure the tower assembly.
Lower Spacer
and Tighten
6.2.5 With the club tightly clamped, place the
laser in the plunger and adjust the
alignment mechanism (up and down) and
the clamping assembly (back and forth),
Figure 6.2.5, until the laser shines directly
within the impact circle created in step
6.1.4. (Since the beam of the laser may not
be perfectly aligned, the laser should be
rotated within the plunger assembly to
make sure that the beam falls within the
circle in all orientations.)
Adjust
Clamp
Assembly
Figure 6.2.7 – Moving Pendulum Assembly
into Position
6.2.8 Loosen the thumbscrew securing the
alignment assembly and lower it until it
rests in its lowest position and tighten in
place using the thumbscrew.
As the
alignment assembly is lowered the
pendulum assembly will come to rest on
the spacer. The club is now ready for
testing, Figure 6.2.8.
Adjust
Lower
Alignment
Assembly
Lower Pendulum
Assembly
Lower
Alignment
Assembly
Figure 6.2.5 – Align Impact Position
6.2.6 Tighten the thumbscrews on the alignment
assembly and the locking screw on the
clamping assembly horizontal adjustment.
6.2.7 Lower the spacer until it rests on the
alignment assembly and tighten in place
using the thumbscrew, Figure 6.2.7.
Figure 6.2.8 – Club Ready for Testing
6
7.
7.2.3 Once the data appears, click on data
collection High Setting #2 and repeat steps
7.2.1 and 7.2.2
Club Testing
7.1 Ensure that the Pendulum Test Console that
was started in step 5.1 is running and that
the system check was successfully
completed.
7.2.4 Repeat step 7.2.3 for data collection at
High Setting #3.
7.1.1 Retract the pendulum until you hear three
clicks.
7.3
7.1.2 Press the pendulum release and allow the
pendulum to strike the clubface.
Repeat step 7.2 collecting data for
Medium Settings #1, #2 and #3. The
pendulum should be retracted until you
hear two clicks in this step.
7.4 Once again repeat step 7.2 collecting data
for Low Settings #1, #2 and #3. The
pendulum should be retracted until you
hear one click in this step.
7.1.3 Repeat steps 7.1.1 and 7.1.2 several times
to ensure that the clubhead is tightly
secured and that no movement has
occurred.
7.2.1 Retract the pendulum until you hear three
clicks.
7.5 Once data has been obtained at the first nine
settings, repeat steps 7.2 through 7.4 for an
additional nine settings until a total of
eighteen data points are acquired. The
software will calculate the characteristic
time based on the slope of a line of best fit
associated with the eighteen data points.
7.2.2 Press the pendulum release and allow the
pendulum to strike the clubface.
8.0 Conformance Determination
7.2 Using the mouse, click on data collection
High Setting #1 in the Pendulum Test
Console.
8.1 If the characteristic time is less than or equal
to 239 µs plus the tolerance then the test is
over and the clubhead conforms to the
Rules of Golf.
Retract Pendulum
and
Press Release
8.2 If the characteristic time is greater than 239
µs plus the tolerance then the test is over
and the clubhead does not conform to the
Rules of Golf.
8.3 Clubface Coatings
8.3.1 In addition to characteristic time and the
confidence interval the software also
evaluates the magnitude of the slope of the
line. An unusually large slope (greater than
20) indicates the possibility of a secondary
coating on the face of the club. In this
instance
additional
evaluations
are
required. These are described in Appendix
A.
Figure 7.2.2 – Club Testing
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Appendix A – Procedure for Evaluating Clubs with Compliant Face Coatings.
Section 8.3 addresses clubs whose clubfaces have a compliant face coating. These are characterized by
exhibiting an unusually large slope (greater than 20) for the line that is fit to the measured data points.
The flow chart below describes how such clubs will be evaluated for conformance.
From the flowchart it can be seen that if the slope of the line is greater than 20 and the characteristic times
at the three test velocities are greater than the limit then a measurement of the coating thickness needs to
be made. This measurement is made using an eXacto FN External Coating Thickness Gauge.
Using the measured coating thickness and the natural log of the slope, Figure A-1 is used in the pendulum
software to determine the appropriate exponent, “k”, (rather than the standard value of 0.33) for the
equation of the line to the fitted pendulum test data of the form:
A + B V-k
8
0.60
0.020"
0.015"
0.55
0.025"
Optimum exponent
0.010"
0.030"
0.50
0.005"
0.040"
0.45
0.050"
0.40
0.060"
0.080"
0.35
<0.0025"
>0.080"
0.30
2.5
3.0
3.5
4.0
4.5
ln(Slope)
Figure A-1 - Variation of Exponent with Slope and Coating Thickness.
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5.0
Appendix B – Procedure for Evaluating Clubs for Conformance to Appendix II
Rule 4c(ii)
This appendix details the test procedure to determine the conformity of a golf clubhead to Appendix II,
Rule 4c(ii) Spring Effect and Dynamic Properties which states:
The design, material and/or construction of, or any treatment to, the clubhead
(which includes the club face) must not:
(ii) incorporate features or technology, including, but not limited to separate
springs or spring features, that have the intent of, or the effect of, unduly
influencing the clubhead’s spring effect
B.1. Summary of Method
Using the pendulum test apparatus, a golf club head is impacted several times by a small steel pendulum.
A characteristic time is developed based on the results of these individual impacts. The characteristic
time is directly related to the flexibility of the golf club head. The characteristic time may not exceed a
predetermined limit anywhere on the club face.
B.2. Significance
B.2.1 This method uses the characteristic time to determine the conformity of a golf clubhead to
Appendix II, Rule 4c(ii) of the Rules of Golf. While this rule applies to all clubs, currently the test
detailed in this appendix will only be applied to driving clubs. The test could be expanded to
include other clubs in future revisions of this test protocol should the need arise.
The characteristic time at any point on the face of the clubhead shall not be greater than 239 µs. A
maximum test tolerance of 18 µs is associated with this test.
B.2.2 Intermediate screening procedures may be used to determine clubhead conformance and increase
testing efficiency. However, the USGA will continue to monitor innovations in design and reserve
the right to conduct additional research when appropriate.
B.2.3 Over time, the procedures outlined in this document may be changed and the test tolerance may be
reduced as test methods are refined.
B.3. Testing Apparatus Set-up and Preparation
Set-up and prepare the pendulum testing apparatus following steps 5.1 through 5.4 of the main test
protocol.
B.4. Club Preparation and Mounting
If there is no shaft in the clubhead, one must be temporarily installed prior to testing.
B.4.1 Determination of Impact Location
B.4.1.1 This test measures the clubhead flexibility at various locations around the face of the clubhead,
including positions near the crown, sole, toe and heel portions of the clubface.
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B.4.1.2 Select an impact point on the clubface for the initial testing and then mount and align the
clubhead following steps 6.2.1 through 6.2.4.
B.4.1.3 With the club tightly clamped, place a Sharpie in the plunger and mark the impact location.
B.4.1.4 Position the pendulum assembly following steps 6.2.6 through 6.2.8. Once the pendulum
assembly is in the test position, place an identifying label near the impact location on the face using
a Sharpie. For example; an impact location on the toe of the face near the crown may be labeled
TC1. The club is now ready for testing.
B.5. Club Testing
Test the club following steps 7.1 through 7.4
B.6. Conformance Determination
B.6.1 If the characteristic time is greater than 239 µs plus the tolerance then the test is over and the
clubhead does not conform to the Rules of Golf.
B.6.2 If the characteristic time is less than or equal to 239 µs plus the tolerance then repeat steps B.4.1
through B.5 at a different position on the face until representative measurements are obtained at the
sole, crown, heel and toe areas of the clubface.
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