Spiral Threads

[jkb_mcg]

Anybody have experience checking true pos. of a hole with a spiral thread? According to the shop manager here, one side of the threads differs from the other side. When I input my minor diameter, the hole size shows up much larger. I think the problem could be occuring because I am using the pitch option with the Auto Circle Feature. The shop is also thinking that since the hole size is coming up larger than it actually is, and I am getting the true position bad, that I shouldn't be using the pitch option on a spiral thread. Since the form of the thread is different, they think the form of the hole is off, and that is screwing up the location. Any ideas?


All help is greatly appreciated!

[Peter Warcholyk]

Would it be possible for you to use a threaded plug in the hole, then measure the od of the plug?
This may be an alternate method to obtain your true position.

ZydecoPete

[John Kingston]

Try putting a thread plug or minor diameter pin in. Measure position of that. Compare numbers. Using the pitch function will just make sure the tip hits in the same part of the thread form. It won't give you a good size, but should give you a good position.
Also, try verifying the position using methods other than the CMM, just to prove you and the CMM are correct.

[bw_bob]

Wpws

[craiger_ny]

...try verifying the position using methods other than the CMM, just to prove you and the CMM are correct.

Sounds like you might have potential for an argument there. Do what John says. Best bet is to do it quietly before the argument starts so you can go in with both guns cocked. If you are new to this get used to it. It is common in this bussiness.

Craig

[John Kingston]

Sounds like you might have potential for an argument there. Do what John says. Best bet is to do it quietly before the argument starts so you can go in with both guns cocked. If you are new to this get used to it. It is common in this bussiness.

Craig

I think you are wrong Craig , no one ever disagrees with people on our field.

Good point about doing it quietly. Have the other inspection data there to pull out when they disagree with the CMM.

[cmmguy]

Anybody have experience checking true pos. of a hole with a spiral thread? According to the shop manager here, one side of the threads differs from the other side. When I input my minor diameter, the hole size shows up much larger. I think the problem could be occuring because I am using the pitch option with the Auto Circle Feature. The shop is also thinking that since the hole size is coming up larger than it actually is, and I am getting the true position bad, that I shouldn't be using the pitch option on a spiral thread. Since the form of the thread is different, they think the form of the hole is off, and that is screwing up the location. Any ideas?


All help is greatly appreciated!

OK, what is a spiral thread?? I thought all threads were "spiral".
And how can a thread have two different sides??

What is the thread callout exactly? Is this a tapered thread??

[craiger_ny]

OK, what is a spiral thread?? I thought all threads were "spiral".
And how can a thread have two different sides??

What is the thread callout exactly? Is this a tapered thread??

I wondered the same. Butress form perhaps?

Craig

[cmmguy]

I wondered the same. Butress form perhaps?

Craig

Yeah a buttress would have different flank angles. If that is the case, he should just size a deltronic type pin for the hole and measure the pin and skip measuring the hole.

btw, thread following should still work with a buttress type. It would not work well with a tapered thread though.

[jkb_mcg]

I wondered the same. Butress form perhaps?

Craig

Here is a picture of a standard 4-40 tap (left) and a spiral-lock tap (right)

See the difference?

[#2#]

Looks to me like the pitch function for an auto circle should work. It will give you location but not size.

[Wes Cisco]

I check sprial-loc thread all the time. Use the pitch function. The fact that the flanks are different does not matter, the priniciples are the same. If you can, fine tune your start/stop locations to catch the crest of the thread. By adjusting them in small increments you should be able to find the crest, even if you can't see it, by watching the changes in reported diameter as you adjust. Do not forget that your start and stop locations should be a multiple of the pitch apart. So for a 40 pitch 1 thread = .025", so you might use start and stop locations .2" apart, (8 times the pitch). Even if you are hitting between crests, with the proper pitch entered, you should hit the same place on the thread each time, giving you good position if not size. HTH

[cmmguy]

Wes,
is that a single start or multistart thread?

Also, i thought that you could put 1/40 into the pitch and it would do the math. (maybe I tried that and it didnt work - I forget)

[Wes Cisco]

Wes,
is that a single start or multistart thread?

Also, i thought that you could put 1/40 into the pitch and it would do the math. (maybe I tried that and it didnt work - I forget)

J,
I have only seen single start spiral-loc threads. There are a proprietary thread form that is a sort of cross between a buttress and a un thread. They require two no-go gages, one for high p.d. and one for ramp. They have become quite popular with many of the oilfield engineers in the last 5 years or so. I think they are supposed to be stronger than standard un threads.
I do not think pc-dmis will do the math for you. .025 is 1/40.

[Mike N.]

I never seen one of those before ?

whats the application?