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Proper gauging of tight tolerance (reamed) holes


Starting to get Involved
I have an order for a large number of castings that need to have a through hole reamed to .2505"--.2510" and need a simple but effective means of gauging these holes.

As you cannot put the same size pin/plug guage into the same sized hole how do I guage these and not give up any of my tolerance?

If I use a a fudge factor of .0002 under (to be able to put the pin into the hole) .2503" deltronic pin as my "GO" and .2512" NO-GO?

What about taking an exact size Deltronic pin and gring a flat (.020") on two sides?

I wish I had air guages but do not, and I really need something my operators/inspectors can use as a quick check at the machine.

Thanks in advance
What about a dial bore gage with a .0001 indicator (this one has a .0005). This way you can also check for roundness.

I just found an image on Google. I have no idea if the company in the link is good or not (just using the pictures).

on a separate note, if the job allows for it, I would get a dedicated ring gage to set the dial bore gage. Setting a dial bore with a micrometer is a little more difficult and allows for some easy errors.

Jen Kirley

Quality and Auditing Expert
Staff member
For a tolerance you describe I would favor a bore gage such as Fowler sells (I have no affiliation) with a 0.00001" resolution. See pages 154 and 155 etc. of the Fowler Catalog.
Just use a telescoping gage and 1" outside mic.
That way you don't have to buy any expensive tools.
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