How to measure pitch diameter on internal acme threads?

[i_r_machinist]

We cut a butt load of stem nuts here, like 1"-.2p-.4l lh acmes. Normally I will ask for the matching stem and fit the nut to it, but sometimes we can't do that. If I was in a production shop I would get go-nogo gages. Over the years I've built up a collection of old stem segments that I keep in a drawer for fitting, but every now and I then get thrown a curve ball. So, How to measure pitch diameter on internal acme threads?
Thanks in advance
i_r_

edit: I just thought of something. I used to work in a shop that had a "gagemaker" system.

 

[Cole2534]

How about some ball bearings and an adjustable parallel? You should only need 4-5 extra (small) hands to make it all work.

 

[BuffDan]

pour some cerrobend/cerrosafe in and measure that. ?

 

[davehud]

Take the time to make and thread a check plug.

 

[mc3608]

Make a Male Gauge. Easy to do.
Should be able to get specs out of Machinery's Handbook.

 

[M4Belisle]

A plug gage will not measure pitch diameter. In fact, a plug gage, doesn't actually measure anything. It will perform a check of the functional size of the thread form. When using a Go/No go set of plug gages, you are simply checking to see if your part falls within a certain range......if the part passes a Go/No Go check, the only thing you have confirmed is if it will assemble with its mating part.
In order to measure pitch diameter you'll either need a set of gage balls or a much better solution is to use an indicating gage with either cone & vee rolls or segments. The style I am referring to would be a comparator gage that is set with a master setting ring, and will compare your part vs the setting ring. Very easy to use and is by far the best method for measuring internal pitch diameter.......expensive? yes, but again by far the best method.

 

[cb750chris]

Dental putty and an optical comparator works. Clean part with alcohol first to make sure you get a good mold.

Sent from my SM-N960U using Tapatalk

 

[M4Belisle]

here is a cross section of pitch diameter segments

 

[Bobnotthecat]

Sir,

I have in the past cut many left hand acme threads in brass, bronze or stainless steel stem nuts. To many to ever count and have always made fitters from whatever scrap that we had lying around made to the maximum size the male thread would ever be using the single wire method to gauge the pitch diameter. Worked fine for us and is a straight forward, practical approach for this class of work.

If you are looking for a way to measure the pitch diameter in a practical, straight forward manner, leave the nut a little long, turning an appropriate length spigot of some random diameter inserting an appropriately sized ball, measure ball to O.D. with mics, then do the math.

That's all I got to say about that.

Luck to you sir,
Bob....not the cat