Measuring internal thread pitch diameter.

[Tin Man]

I can't seem to find a reasonable priced thread gauge to check pitch diameter on internal threads. (Like 3 wire but internal) I don't trust go/no go because I want a measurement not a "feel". Example: If you were threading a 6" dia. nut and checking with a no go and the middle was looser and out of spec, you wouldn't know how much or if it was in or out of spec. I've heard of doing the ball bearing thing which makes the most sense to me. I just cannot believe nobody has made a reasonably priced tool with exchangeable balls (like wire set sizes) that would do this. I've seen the spring gauges too but really looking for a universal tool that doesn't cost a fortune and does a huge range of threads like a inexpensive set of wires will. Again I'm shocked nobody has done this. Maybe I should patent / manufacture one? I have a couple ideas but can't belive nobody has beat me to it.

 

[michiganbuck]

I think Gordon's thread digital thread calipers could do that.

Measure Internal Thread Pitch Diameter|Flexible Measuring Systems

For getting internal thread pitch diameter measurement tools such as BSP, Acme, stub acme, buttress, API, etc. Contact flexible measuring systems @ +45 7555 3854.

fms-dk.com

 

[Mr. Atoz]

Unless you are making "special" threads, I don't understand why you can't use a go no/go gage. Thousands of other shops find that they do just find.

 

[Tin Man]

Unless you are making "special" threads, I don't understand why you can't use a go no/go gage. Thousands of other shops find that they do just find.

What if you had a thread in a bore 6" long, the no go guage fit snug on the end of the threads, then started getting loose in the middle. You wouldn't have any idea if the treads were just looser, or out of spec too loose. You'd only know they were looser. Tell me the pitch diameter of the loose part in the center of the thread. You couldn't. Only that it was looser. And we all know just because something threads into something doesn't mean the threads are good.

 

[Tin Man]

I think Gordon's thread digital thread calipers could do that.

Measure Internal Thread Pitch Diameter|Flexible Measuring Systems

For getting internal thread pitch diameter measurement tools such as BSP, Acme, stub acme, buttress, API, etc. Contact flexible measuring systems @ +45 7555 3854.

fms-dk.com

This is a lot like what I had in mind to make. I bet it's expensive and you'd have to have a bunch of the calibration tools to be covered for different pitches. I was thinking of something with balls then you could do the math like using wires.

 

[guythatbrews]

Pistol grip type dial gauges are made for this but they are $$$, especially if you consider you'd need more than one to get sny kind of range.

If you just want a comparison method cobble some ball extensions on a caliper. You could also use the cobbled caliper to get a good idea of actual size if you had a thread ring gauge to calibrate it with.

 

[William Lynn]

What if you had a thread in a bore 6" long, the no go guage fit snug on the end of the threads, then started getting loose in the middle. You wouldn't have any idea if the treads were just looser, or out of spec too loose. You'd only know they were looser. Tell me the pitch diameter of the loose part in the center of the thread. You couldn't. Only that it was looser. And we all know just because something threads into something doesn't mean the threads are good.

Have you actually had a thread gage get loose in the middle of a just machined part, while both ends had a nice fit? I never have, only in a used part where the stress of usage distorted the part.

 

[gbent]

Is this a real concern, or a hypothetical? When you make your device, make it so you can measure the roundness of a thread milled internal thread.

 

[bigjon61]

We had the Fowler truck stop at our shop a few years back and they had a holematic that you could get custom anvils made for threads. Looked fun, but pricey.

 

[michiganbuck]

Thread gauge calipers...not that expensive
About $220 USD for the base model and perhaps another 220 for the different gauge end jaws
Way less than buying thread gauges for a number of threads..and pretty quick to use.

Measure Internal Thread Pitch Diameter|Flexible Measuring Systems

For getting internal thread pitch diameter measurement tools such as BSP, Acme, stub acme, buttress, API, etc. Contact flexible measuring systems @ +45 7555 3854.

fms-dk.com

 

[Tin Man]

Have you actually had a thread gage get loose in the middle of a just machined part, while both ends had a nice fit? I never have, only in a used part where the stress of usage distorted the part.

I have inspected threads that were made on a machine that had an issue in a ceartain part of the way and created a part that way so yes. Anything is possible, That's why people inspect parts. You never know what might be wrong unless you can find it. I tend not to assume much.

 

[guythatbrews]

I have inspected threads that were made on a machine that had an issue in a ceartain part of the way and created a part that way so yes. Anything is possible, That's why people inspect parts. You never know what might be wrong unless you can find it. I tend not to assume much.

I've been bit in the hindquarters assuming stuff.

If the ends are good with a plug gauge just a simple caliper attachment is all you need to compare the middle with the end.

I don't know what it's called but the make a thing like a mueller shallow diameter gauge, but it's a table rather than a rail setup. The measuring tips stick straight up. You can change the tips and they read in tenths. Use a spacer to raise the part up off the table. Check the end thread and zero. Remove the spacer so now the part is on the table and check the middle part of the thread.

 

[EPAIII]

Your lathe would have to be cutting on a taper to make the outer threads OK but the ones further inside that hole larger.

So just check your lathe for a straight cut: for no taper. If there is no taper, then the threads should be the same size all down the hole.

I like the caliper accessories mentioned above. They look like they would be fast and easy to use. Don't know about the accuracy.

Another approach would be to buy a go-no go gauge set. That should check near the end(s). And then buy an extra go gauge and grind off all but the first two or three threads so it can check at different distances down the hole.

What if you had a thread in a bore 6" long, the no go guage fit snug on the end of the threads, then started getting loose in the middle. You wouldn't have any idea if the treads were just looser, or out of spec too loose. You'd only know they were looser. Tell me the pitch diameter of the loose part in the center of the thread. You couldn't. Only that it was looser. And we all know just because something threads into something doesn't mean the threads are good.

 

[guythatbrews]

Different gauges that will work.

Horizontal stands [Inside diameter measuring instruments] | CITIZEN FINEDEVICE CO.,LTD.

Internal Diameter-Grooves - Pin Seal Diameter Gages - Gagemaker Thread Measuring Instruments - Measuring Instruments

www.threadcheck.com

Internal Pitch Diameter Gages - Internal Pitch Diameter (1-1/2” to 27" Diameters) - Straight Thread Pitch Diameter - Pitch Diameter Gages - Gagemaker Thread Measuring Instruments - Measuring Instruments

www.threadcheck.com

 

[R. Dan]

Johnson Gage: https://www.johnsongage.com/internal-thread-inspection-systems/

 

[winger]

I think I gave the book away, but one of my old die books had a picture of a internal thread measuring gage made from an inside mic.
A correct sized ball was bonded to the fixed end and the removable part. A slotted spacer was used that could be pulled out to allow the unit to collapse and take out to read.
Because of the angle it wouldn't be totally accurate but could be used as a comparator with a gage part.
Hope my description makes sense without the picture.
Dave

 

[michiganbuck]

A Go and No gauge might be made (lathe-turned) that only hits the part at the pitch diameter, and tried at both ends of the part. Yes using a more narrow bii/insert than 60 and being flat (or a radius) at the gauge OD.
One might stay a half thow away from limits just to add safety.

 

[gregormarwick]

A lot of the threaded parts I have made over the years have been too big to use a go/nogo. One place I worked at early in my career had a Gagemaker set which worked well enough but the whole system (the software in particular) was extremely US-centric and didn't support many threadforms. IDK if this is still the case or not, but I have never missed it.

A good 50% of the time an internal thread has a concentric OD - a simple micrometer and a single ball is an easy way to find the PD in this case.

When there is no concentric OD to measure from, three balls, a gauge block and a stick mic will get you there but it's a bit of a three-handed job. At my last place I butchered a stick mic for the sole purpose of this - ground a vee-cup in one anvil to locate the top ball, and made an anvil for the other end that had a straight vee cut in it to saddle two balls at the bottom. Was effective, but still not very easy to use.

I did like the look of Gordon's system and always intended to buy one but never got around to it.

 

[Tin Man]

Thanks for the ideas.

 

[kenton]

Would 3 bearing balls and an adjustable parallel work? What size threads are you trying to measure?