Inspection of tight toleranced holes.

[davidlee]

Hi there I have been tossing this question around to diffrent people and it seems everyone has a diffrent answer. Here goes if you have a hole say its 1.000 +.0001 -.0002 what size pins would you used for your go and no go. I would chose a .9996 and a .9999 pin. To me you need .0002 clearance for a pin to fit into the correctly sized hole. I don't see how a size for size pin would fit even though that is what some of the inspectors say. I also asked our GD&T guru if there was a standard for what size pin will fit in what size hole he did not know of any inspection standard when it comes to this situation. Thanks for your feedback.

Merry Christmas & Happy New Year to All

[matsuura]

I would say that you are right,you need at least .0002 of clearance, that say if you have a lot of hole to inspect you could use a bore gages.

happy holidays

[fpworks]

You have to use a bore gage for holes with tolerances that tight. Preferrably a comparator type.

If you have a lot of holes to inspect, air gages all the way.

[planar39]

what we had when i was in a total edm shop was a smartscope, its about 30-40k, this is a computer attached to an x-y axis, and the z axis is a camera,
it zooms up and down, lovely for checking many of the same parts.

the comp. uses the camera image to identify and measure, super accurate,

maybe a bit off topic cause, for your question i would use a 1.0001 and .9998 because that is what id assume the customer would use.

[miljnor]

that is what id assume the customer would use.

This is a common mistake made by almost everyone at one time or another.

Always ask the for the QC inspector of the company that you are building for and ask what their inspection method is. They are always welcome for anything that makes their job easier.

[matsuura]

the for the.

[davidlee]

Ok here is some more info about the situation. First of all the hole size is actually .1245 so I don’t know of any bore gages that will go into this size hole. I was also thinking that normal shop pins are typically -.0002 in size although I have deltronic pins that are dead on in .0001 increments. Thanks for the replies

[fpworks]

Subito makes one that we used to measure 0.1181" -0.00008", -0.00020"

That is a tolerance window of 0.00012

(it was a 3mm hole with a minus 2, minus 5 micron tolerance)

[RICHARD ZASTROW]

davidlee Had the same problem. .0130" dia. .0003" plus true position .0005" on multi-hole grid pattern. Used CMM w/toolmakers scope attached to CCTV. Worked fine. I'd go with the scope. Doesn't need to be as elaborate as the above example. At that time I was employed by a Fortune 50 corporation.

[fpworks]

Richard,
Can the CCTV measure diameters along the depth of the holes? Typically, if holes have this tight of tolerances, the diameter is required to be held along the entire depth of the hole.

I would imaging that any optical system would have trouble with this.

Justin

[RICHARD ZASTROW]

Good point! These scopes have a very small focal length. You must be able to provide a source of light to illuminate the measuring point. We had to measure at the surface since that was where the critical point was. I would use optical fiber to illuminate point of measurement from opposite side. This may be getting too complicated (expensive) for the app.