Checking thread depth?

[Quality ish]

These CMMs are amazing critters...

Has anyone found a way to train one to measure thread depth?

[William Johnson]

nope

[UKCMM]

Some things are not meant to be checked on a CMM and thread depths is one unless you are going to put a thread gauge of known length and probe the end of the gauge after screwing in hole, not very practical as would slow the measurement routine down.

[Darrollh]

I try telling my manager that and they insist I check them d@#$ threads! Why when you have to 100% them anyways!

[measurestuff413]

I have done this before.

The only way is to have the thread gage ground down to the lead. Then measure the part...put a program stop to tell the operator to insert the gage...then measure the end of the gage.

As said above...this will add program time. However, we did it for a final inspection OP where we were measuring hundreds of parts and had about a dozen ground gages. This worked out to be faster than having someone stand at a shadowgraph.

[Kai Kendall]

I think it's possible. I have, for example, had CMM machines measure a series of self-centering points in the pitch of threads (technique for another thread), so I guess it would be possible to simply ask the machine where the change (end of thread) occurs. Will take this as a challenge, since I just love getting machines to perform tasks generally considered impossible...

[Schrocknroll]

I think it's possible. I have, for example, had CMM machines measure a series of self-centering points in the pitch of threads (technique for another thread), so I guess it would be possible to simply ask the machine where the change (end of thread) occurs. Will take this as a challenge, since I just love getting machines to perform tasks generally considered impossible...

Be careful with that. Thread depth is depth of usable threads, e.g. the depth a thread go gage will go. Just using the CMM to check for the presence of threads won't give you that answer.

It is good to push the limits of what is thought to be possible, but don't do it at the expense of accuracy.

[Kai Kendall]

Actually, even pitch diameter can be accurately reported, provided one uses a ball size that falls within the acceptable range of thread measuring wires. That does not necessarily mean it's useable, of course, but does report the most critical aspect of thread quality.

[measurestuff413]

To the best of my knowledge, you can't measure PD with PC DMIS. Can you please show us some code?

[Mike Ruff]

I can get in and out of a hole with a thread gage a lot faster than a CMM can measure a cylinder with pitch, zero out on it, and then scan opposing sides to come up with a number that is most likely not repeatable. Plus the time it takes to program all of the trig (which would also need to take into account the tip size from the calibration, not just 1mm, 2mm, etc.)...

[louisd]

presuming your threads are under an inch in diameter, and are bores, yeah the ground inserts are the only way to go.
if they are >1" and are bosses, you might be able to get creative like Kai Kendall is suggesting... otherwise wrong tool for the task.

[Quality ish]

I suspected as much, but I hoped...

Thanks all, for your input.