Measuring Large Small Holes

RJSakowski

H-M Supporter - Gold Member
H-M Supporter Gold Member
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Feb 1, 2015
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When measuring the diameter of small holes, my favorite tool is a pin gage. I have sets up to 1/2" but yesterday, I needed to measure a .903" hole. Ideally, I would have a full set of pins to 1" but at somewhere near a $700 even for an import set, that's an expensive bunch of metrology. I used a .500" pin and a .403" pin side by side to make the measurement. It worked great. A .500" + a.402" was loose, a 500" + a .404" was a no-go, and a .500" + a .403" was just snug.
 
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RJ,

How about a telescoping gage? Man, I love those things and get a lot of mileage out of them.


Ray
 
Another choice is Brown & Sharpe tapered hole gages; one side is radiused, the other flat; they are used in pairs flat side to flat side and wedged into the hole with one end protruding from the hole and measured with a micrometer other options are small hole gages, telescoping gages and inside mikes. I also have a set of B&S flat plug gages, 3/8 to 2" by 1/16ths, good for detecting taper and fit in nominal size holes.
 
Tri mic , they are expensive and limited range but nice .
The only Tri Mic (Made by B&S) that I am aware of is a OD micrometer with three contact surfaces and is used to detect 3 lobed out of roundness and diameters of 3 or 6 fluted of end mills; Is your post of something entirely different?
 
Intrimik I believe, John.
Intrimik I believe, John.
OK, that makes more sense; both are B&S products Intrimics are quite expensive even used and of quite limited range I see lots of them on E Bay and wonder if they ever sell them at the (wished for) prices. They are not a tool that the average machinist or even tool maker would be able to afford; I'd think only an inspection department of a wealthy company or the government would have bought them.
 
They are quite handy for catching 3 jaw eggs on thin parts. I've got a couple stashed away someplace. But then, I was allowed to clean out some instruments from a company I worked for. I have a few things most hobbyists and even smaller shops aren't likely to have (Ultrasonic thickness mic, anyone? Profilometer?). I didn't get everything I wanted, but some interesting stuff nonetheless.
 
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