Does anyone have experience with thread "timing?"

[billthebutcher]

...also known as thread "clocking?" It is a gauge point on the thread surface lying on a plane coincident to the thread axis. It is dimensioned off of the thread axis by means of a basic dimension. It is also dimensioned (and toleranced) off the the perpedicular surface that the threaded hole is drilled in. The purpose of the gauge point is to ensure that the mating component stops at a fairly precise angular orientation when screwed in all the way.

I'm trying to find a way to measure this. The thread is an internal ACME thread with a pitch diameter of approximately 1.25", so it is fairly large. The tolerance on the "timing dimension" is +/-.0015. I have been using repro-rubber mold compound on the optical comparator, but this is not practical for any kind of regular inspection - only first articles.

I'd appreciate any advice.

 

[redpicker]

I would think that it would be much easier to design a gauge to verify the mating component will stop at the reqruied position. This would not only verify* the "timing dimension" but provide a functional check that the threads are suitable.

*Of course, the verification would only be valid if the thread elements (pitch diameter, thread form, thread lead, etc...) are within acceptable limits. The thread elements would have to be verified independantly.

rp

 

[MikeHalloran]

All I can think of is a tiny gage ball (to touch the Acme thread flanks) projecting from a minor diameter-ish cylinder with a flange to engage the perpendicular surface, and some kind of flag to show angular orientation of the ball where it stops as it's gently screwed into the part.

Or, similarly, a 'perfect master' of the mating part, made by a gage maker.


It would be easier for the only serious clocked threads with which I have experience, torpedo tube breech rings.



Mike Halloran
Pembroke Pines, FL, USA

 

[billthebutcher]

Thanks redpicker. I've drawn up some gauge concepts, but I think gauge R&R dictates that the measuring device is supposed to have something like 1/4 of the resolution of the tolerance on the dimension to be measured. I don't think a tolerance of +/-.00016 is possible for a gauge. It might not even be possible for a contour reader.

 

[billthebutcher]

Mike, this thread clocking is for the quick-change barrel on a machine gun, so both of our applications relate to weaponry. The ball idea is a definite possibility - I will have to float that idea to a gauge-maker.

Thanks for your response.

 

[Duwe6]

Try making a Go-NoGo gage with a +0.010" end and a -0.010" end. Anything that fails this gage can be measured using balls or a replication.

 

[billthebutcher]

I'm not sure what you mean, Duwe.

 

[Duwe6]

Time one male thread at +0.001, and another at -0.001, or just put a shoulder on the back end of the male thread and scribe or laser etch +1, 0, -1 marks on it. Screw it into your ID thread and see where it ends up. This assumes that there is a "feature" on the ID threaded part that can be 'timed' off of.

Old scool gunsmithing.

 

[unclesyd]

How good was the starting hole? What you need is Thread Squareness gage of some description. There are several different approaches listed below.

Hole location plugs

You might be able to use this type with by swinging an indicator if the pin is long enough.

http://www.gsgage.com/content/our_products/thread_plugs.asp

Thread Squareness Gages.
Page 37 of the pdf.

http://www.southwesterngage.com/Hemcopdf.pdf

Essentially the same as above.

http://www.zerogage.com/v4/go.gnf?s...late=h2_i2_w1_f1_001&itemId=5376&product=2240

A little different approach using an expanding arbor.
See page 7

http://www.hydralock.com/images/stories/pdfs/p7.pdf

 

[billthebutcher]

Duwe: I think I understand what you mean now. Thank you.

unclesyd: Thanks for the links - I was actually wondering how to check true position of a pitch diameter. The pdf and last link you provided looks like a solution.

I appreciate all the responses guys, thank you.