Questioning the CT machines accuracy

[Harrington77]

Long time reader first post in a while.

I work in manufacturing and quality, we do a lot of gauge R and R testing. Basically try to eliminate as many variables as possible. I have been having a good look at the CT Machine that they use to test drivers and I noticed that the head is not held in place for the test. Instead the shaft is clamped a specific distance from the pendulum. To me this means the shaft has an influence on the test i.e. If you have a soft flexible shaft surly the pendulum will stay on the shaft longer and vice versa. Arent they supposed to be testing the head and not the shaft.

[Fade]

Yes, they are supposed to test the head only, not the whole club (incl. shaft). But if they clamped the head into - say - a 2 kg vice, they would be effectively changing the mass of the head by a factor of ~ 10x, and this would increase the measured COR significantly. Ideally, to test the head alone, they would hang it from a string. And by that logic, a flexible shaft would be expected to provide a better measurement than a rigid shaft.

[Fade]

You will be interested in this (background info on the test procedure):

 

http://www.jga.or.jp/jga/html/rules/image/info3_pendulum_tec200311_en.pdf

[arbeck]

That's one of the reasons there is a tolerance built in to the test. The limit is 239, the tolerance is 18, which means you don't fail until you go above 257. What Callaway and other tour companies are doing though is pulling heads that measure around 250. They are above the limit, but below the allowed tolerance. However, even the measurement device has a tolerance. So you really can't complain when your head that is above the limit fails the test, even if it didn't fail your test.

 

The chance of a head that was actually at the 239 limit failing any test is pretty slim.

[Stuart_G]

> @Fade said:

> You will be interested in this (background info on the test procedure):

>

> http://www.jga.or.jp/jga/html/rules/image/info3_pendulum_tec200311_en.pdf

 

I found it really interesting that the gage results of 6us was almost entirely attributed to operator variability - which came down to the operator being able to place the club in the machine so that it actually hit the center of the face. Which tells us the machine is really pretty accurate (or really repeatable) if you take out the human component.

 

The current (?) procedure guide mentions the use of a template to help the operator find the center of the face but I don't see any mention of that in the paper you provided a link to. I wonder if the use of the template is different and was added after that study to increase the repeatability of the test?

 

https://www.usga.org/content/dam/usga/pdf/Equipment/TPX3004-procedure-for-measuring-the-flexibility-of-a-golf-clubhead.pdf