Using three pin gauges to extend measurement range

I could not resist getting a gauge pin set…0.061 to 0.250 covers a good range that snap gauges can’t.

Edit: these are minus sets, no bigger than the stated diameter, no smaller than two tenths under.

 

By using two pins the check a hole you can nearly double the range.

 

By using two pins the check a hole you can nearly double the range.

You can extend the range slightly more by using three pins. The math gets more complicated but if you have CAD capability, the CAD math engine will solve it easily. If you use three pins differing by +/- .0001, the diameter is 2.1547 x the middle pin diameter.

 

You can extend the range slightly more by using three pins. The math gets more complicated but if you have CAD capability, the CAD math engine will solve it easily. If you use three pins differing by +/- .0001, the diameter is 2.1547 x the middle pin diameter.

yes, but holding 3 pins in line becomes a little more difficult. You can do it, but you need to use 2 bars, sticks whatever to keep them in line... if they triangle out on you, you lose your measurement.

 

yes, but holding 3 pins in line becomes a little more difficult. You can do it, but you need to use 2 bars, sticks whatever to keep them in line... if they triangle out on you, you lose your measurement.

It isn't three pins in line. They form a triangle. It is actually more stable than two pins as two pins have to be exactly parallel to each other to get an accurate measurement.

An added bonus is that three pins can extend the precision of the measurement. My pin sets all measure out at +.0002 or -.0002 from nominal, depending on whether a plus or minus set but the pins increase in .001" increments so the best I can do is to measure to within .001" However if I use three pins, two of which are slightly under the radius of the hole, a third pin will actually resolve to about a tenth. It requires some math to do this but my CAD program comes to the rescue for that.

 

If you use three pins differing by +/- .0001, the diameter is 2.1547 x the middle pin diameter.

RJ, this is really interesting, but not sure what you mean? Do you really mean 0.0001?

 

RJ, this is really interesting, but not sure what you mean? Do you really mean 0.0001?

Here is an illustration.

 

Really interesting. I could make a table showing the hole size formed by the three adjacent pins all the way through the set. Anybody ever do that? Oh man, I wish it would rain around here so I can spreadsheet this out!

 

RJ beat me to it!

 

Excellent, thank you guys! So now I want to figure out the math without the cad package and work out tables for the three pins (X-0.001, X, and X+0.001), let X run from 0.062 to 0.249. Now THAT would really expand the range. If it's too sparse a set, then we need the arbitrary solution for three diameters and the superscribed circle.

Fun!