[jilldwr]

I'm having some discussion with a machinist we hired regarding the use of a no-go gage. He ran a bunch of parts that when I inspected with the no-go gage, I could get the gage into the hole with little or no pressure. It stops about 3/16" into the hole, but if I push it a bit, just a bit, it goes all the way thru. I say that's an oversize bore, he says if it stops on its own with no pressure, it's good. Now I can't find the standard anywhere on how to measure with a no-go gage but I'm guessing thats why they call it a "No-Go gage"!!!

ANyone know where it spells out the proper use of a no-go gage? I can't find it in the machinerys handbook.

Thanks
DW.

[ERUS]

Depends on the hole conditions specified on the print.

If it is your own part then its at your discretion. If I was machining that part I would consider it a bad part. The fact that the no-go can be easily pushed says the hole is bad. A 0.0001" \ 0.0025mm of in inch interference is very difficult to force in harder materials.

[handlewanker]

Hi....if the No Go just enters with a bit of hesitation then the hole is right at top limit according to the drawing......if the gauge goes in all the way without any tightness it's a fail......if the GO end won't go in it's a fail too as the hole is undersize and below bottom limit.

Usually for the operator's guidance, the rule is the No Go MUSN'T go in at all.

When you're a machine operator making production parts with holes you haven't got time or the knowledge to measure the hole diam....it's Go or No go......no argument.

When I tooled up the Nakamuras for production, the gauge rate was 1 in 10........if a hole failed to gauge on the tenth part the whole previous nine parts were scrap........no time to mess with nit picking individual hole measuring or re-work......batch parts were in the region of 50,000 until we stopped making for stock and went to the "just in time" principle..
Ian.

[underthetire]

I guess it would depend on if the plug gauges came from a minus or nominal or plus set. If it was a minus set, then technically the hole can be right on the high side, one of the others it's a bad hole.

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[rcs60]

if the no go pin goes then it should be considered out of tolerance
if you have zz - tolerance pins then the pin is size -.0002 which could mean if the gauge is actually -.0002 you might be able to push the pin thru the hole and still be in tolerance
these should be pull off line for evaluation for size roundness ect before being called good pcs.
if you have x - tolerance then the pin is -.00004 and would always be considered out of tolerance
if it is a + pin then the no go even going a little bit makes it out of tolerance

[not_in_use]

In our shop if the No-Go goes even a little it's out of tolerance. That's why they're called NO-GO. Your machinist is pulling your leg.

[jilldwr]

Well, I got the final word from Vermont Gage who sent me this response to my email:

"Please see the attached excerpt from ISO 1938. It clearly states that the No-Go is not allowed to enter the part. You may also review ASME B89.1.7.3.1-2001, Guidelines for Decision Rules: Considering Measurement Uncertainty in Determining Conformance to Specification. This standard takes the 10% Rule (Guard Banding as used in Go/No-Go Gages) and expands upon it.

The bottom line is that the Go needs to pass through the entire length of the hole freely and the No-Go should not fit. Neither gage should be forced.

If you would like to take a deeper dive, see Mill-STD-120 and Mil-S-45662A. Both of these standards have been discontinued but, give a background for the reasoning behind these gages and others."

That pretty much seals the deal! Thanks to Vermont Gage for a concise and timely response.

D.W.