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Thread measurements

Will Henry

Most are familiar with the use of thread wires to measure the pitch diameter of a thread and one can use wires and produce excellent fitment. I use the thread wires to produce gauges for popular threads for barrel tenons (this refers, of course, to vee threads as are found on most barrels). These gauges are cut to minimum and maximum pitch diameter for each thread. I can check for fit in a given receiver, and cut the thread to the appropriate size. This eliminates the need to rely on the "cut and try" method to fit the barrel threads. One can measure the thread being cut on the barrel with PeeDee wires but they are kind of a pain to use (I always drop them at least twice per job) and for this purpose, not necessary. All we are trying to do here is a comparative measurement which can be copied and checked easily. For this purpose a measurement in the thread groove with a dial caliper s sufficient. Now, this measurement is absolutely meaningless in any other context but to duplicate a thread PD it works just fine.
Today I was cutting threads for a Howa action (metric 26x1.5mm). I didn't have the original barrel from the action but I did have three different gauges which I had cut previously so I tried them in the action. The largest gauge threaded in with just a bit of drag. Perfect. I measured the diameter of the gauge, in one thread groove, with my old Mititoyo caliper and got a measurement of .970". Now, this isn't the pitch diameter. It is measured too deep in the thread and on the angle of the thread so it is a comparative measurement only; but that's all I need. I'll note here, this measurement is specific to this one dial caliper. I have five different calipers and they will give five different measurements. This is because the thickness of the blades vary from instrument to instrument. In this case though, I cut the thread til it measures .970 with the same old Mititoyo caliper with which I measured the gauge. I try the receiver on the barrel and it fits perfectly, just like the gauge. This is a lot better than just guessing at it and trying the thread five or six times until it fits. It's not as precise as wires and it does not yield a definite measurement but it does enable you to cut a thread which fits the first time.
As I said, this measurement is essentially useless for any other purpose and, if you want to record a positive measurement so that you can produce a barrel for this action in the future, you'll want to measure the pitch diameter with wires and record that. I have been using the caliper method for a quick and dirty dimension this way for forty years and it works and is repeatable. WH
 
Will Henry said:
Most are familiar with the use of thread wires to measure the pitch diameter of a thread and one can use wires and produce excellent fitment. I use the thread wires to produce gauges for popular threads for barrel tenons (this refers, of course, to vee threads as are found on most barrels). These gauges are cut to minimum and maximum pitch diameter for each thread. I can check for fit in a given receiver, and cut the thread to the appropriate size. This eliminates the need to rely on the "cut and try" method to fit the barrel threads. One can measure the thread being cut on the barrel with PeeDee wires but they are kind of a pain to use (I always drop them at least twice per job) and for this purpose, not necessary. All we are trying to do here is a comparative measurement which can be copied and checked easily. For this purpose a measurement in the thread groove with a dial caliper s sufficient. Now, this measurement is absolutely meaningless in any other context but to duplicate a thread PD it works just fine.
Today I was cutting threads for a Howa action (metric 26x1.5mm). I didn't have the original barrel from the action but I did have three different gauges which I had cut previously so I tried them in the action. The largest gauge threaded in with just a bit of drag. Perfect. I measured the diameter of the gauge, in one thread groove, with my old Mititoyo caliper and got a measurement of .970". Now, this isn't the pitch diameter. It is measured too deep in the thread and on the angle of the thread so it is a comparative measurement only; but that's all I need. I'll note here, this measurement is specific to this one dial caliper. I have five different calipers and they will give five different measurements. This is because the thickness of the blades vary from instrument to instrument. In this case though, I cut the thread til it measures .970 with the same old Mititoyo caliper with which I measured the gauge. I try the receiver on the barrel and it fits perfectly, just like the gauge. This is a lot better than just guessing at it and trying the thread five or six times until it fits. It's not as precise as wires and it does not yield a definite measurement but it does enable you to cut a thread which fits the first time.
As I said, this measurement is essentially useless for any other purpose and, if you want to record a positive measurement so that you can produce a barrel for this action in the future, you'll want to measure the pitch diameter with wires and record that. I have been using the caliper method for a quick and dirty dimension this way for forty years and it works and is repeatable. WH
Click to expand...
that is a good idea- even for a guy like me who only does my own - wouldnt take much time. Do you use a dab of grease to stick the wires to the threads when measuring with them? Thanks
 
I use a thread pitch mic. Cut my tennon diameter to the large spec, then measure the pitch when threading, stop at the large spec and check fit from there. If you want to qualify your mic check it on a standard. Makes life easy when you can refer to the machinery handbook for thread specs and cut to the measurement.
 
hoz53 said:
that is a good idea- even for a guy like me who only does my own - wouldnt take much time. Do you use a dab of grease to stick the wires to the threads when measuring with them? Thanks
Click to expand...
Yes, I use some grease to hold the wires in place. Works better when the workpiece is cold. I use the caliper method to duplicate the pitch diameter of another piece but to cut to a specified diameter where no gauge or other example is available, I use wires. Oh, thread mikes are great too but not everyone has them and, when duplicating a piece, you don't need them. They are great when working to a spec. WH
 
Will Henry said:
Yes, I use some grease to hold the wires in place. Works better when the workpiece is cold. I use the caliper method to duplicate the pitch diameter of another piece but to cut to a specified diameter where no gauge or other example is available, I use wires. Oh, thread mikes are great too but not everyone has them and, when duplicating a piece, you don't need them. They are great when working to a spec. WH
Click to expand...
Thank You for all that. I appreciate it. I just do my barrels for myself, so I dont have to fit them to anybodys spec, so i just thread them until they fit,-- your caliper/sample method would be handy.
 
akajun said:
The fact that you can buy an import thread pitch mic with all angles for cheap, and they are actually pretty good accurate mics, has stopped me from using wires any longer except on acme threads.
Click to expand...
Yep, Shars tool has a pretty decent set. They aren’t a Starrett by any means but the do just fine for a guy like me that does a couple barrels and muzzles a year.
 
wi50shooter said:
Yep, Shars tool has a pretty decent set. They aren’t a Starrett by any means but the do just fine for a guy like me that does a couple barrels and muzzles a year.
Click to expand...

Link to specific set? I've hesitated buying thread mics because of the cost on starrett/mitutoyos for something that won't get a lot of work.
 
I have wires and I have SHARS 0-1 and 1-2 thread mics. I use the mics 99% of the time to see how close I am to approaching a 3A fit. At that point I begin taking a pass and manually fitting the action. I pass until the action threads on without resistance, measure the PD to record and then Finish the shoulder face to be square to the threads prior to shortening the tenon and reaming the chamber
 
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