Calibrating Thread Mikes Without Standards?

[tobnpr]

Recently picked up a couple of Starrett thread mikes off Fleabay...both sans standards.

Absent calibration standards- is there any reason I cannot use the trusty Pee Dee's to get a PD over the wires, and adjust the thread mikes (if needed) to match?

Or, wouldn't any plug gage (known PD) within the size/pitch range serve the same purpose?

Something else?

 

[PeteM]

Either method should work.

A certified thread plug gage might even satisfy QC calibration requirements. You need to pick one where the thread mic anvils can't bottom in the root.

The thread wires used to create a "master" and then that "master" used to calibrate the mic would be more a home shop work around IMO.

 

[Conrad Hoffman]

How do you 'spose they certify the standards? My guess is wires plus optical for the geometry. If the geometry is off, nothing else will matter.

 

[litlerob1]

I would ask Mike what he thinks. I mean if it's Mike you are calibrating, he should have a say in it.

You can buy Standards. The problem you are going to have, is every time you change Anvils, you're going to need to qualify something.

R

 

[tobnpr]

The ones I bought are pitch-range specific, anvils are not interchangeable.
Sorry about the phonetic spelling. "Mics" better?

 

[Peter from Holland]

I used a tap for calibrating once

Peter

 

[WizardOfBoz]

Or, wouldn't any plug gage (known PD) within the size/pitch range serve the same purpose?

Purpose dependent I think. If you have to provide customers with NIST traceable documenttion of your standards, no. If you have a very good go/no go plug change that states the exact size, and what you want is a good indication of size, perhaps. If you have a production run where you just want to test interpart variability or trending, maybe the plug gage (or a "known good" part) is all you need.

I tend to go overboard in measurement. For your amusement, there's a interesting discussion of how one calibrates plug gages, from Mahr, here.

 

[Conrad Hoffman]

As a curiosity, the thread wire formulas are inexact. The error is usually very small but can be significant for certain multi-start threads. W.F. Vogel worked out an exact solution in his book, The exact over-wire measurement of screws, gears, splines, and worms, which can be a bit hard to find.

IMO, when measuring very small/fine threads, you have to be careful not to brinell the thread while measuring it. I prefer optical, with the part held at the helix angle and measurements made off the center-line and doubled.

 

[Mike1974]

I didn't see, but what sizes? Captain obvious here, but 0-1" don't need a standard, just zero the mic and adjust the lower anvil (depending on type) to get zero. You said these were pitch specific, so if 0-1" just adjust barrel so it is zero at zero. For larger, 1"+, you will need a standard. You could hack it with something *if* you know what the pitch diameter is up front.

 

[tobnpr]

^^^^
Thanks- actually, it wasn't obvious to me on the 0-1" that "zeroing" same as an external mic was correct, so good to know that.

"Just" a riflesmith here, not fabbing highly critical parts; but most threads are cut to class 3 specs and need to insure interchangeability of barrels and muzzle devices. No aversion to wires, just looking to speed up the process without unduly affecting accuracy.

 

[Limy Sami]

^^^^
Thanks- actually, it wasn't obvious to me on the 0-1" that "zeroing" same as an external mic was correct, so good to know that.

"Just" a riflesmith here, not fabbing highly critical parts; but most threads are cut to class 3 specs and need to insure interchangeability of barrels and muzzle devices. No aversion to wires, just looking to speed up the process without unduly affecting accuracy.

Make / get yourself the thread ring gauges you need, that way there is no argument.