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Wed, 13 Aug 1997 10:06:50 -0500 |
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Richard,
I have taught many classes in board inspection. This subject always seems to come up. My answer is always the same. I recommend the use of a "minus" pin gage set. A minus pin gage is "typically about .0003" smaller than the size indicated. This avoids confusion when trying to defend a hole size at bottom tolerance. My logic is simple, I believe that an .045 pin will not fit into an O.045 hole. Using an .044 pin to check an .045" holes lends itself to the question " what if the hole is .0445?. I have not ran across any customer that objected to the use of a .045 minus pin to check a .045" hole. If a Customer squawks at that, then there are deeper issues than just a hole size. Just as an added note, unless you are dealing with a critical hole size such as a press fit connector hole, generally I have found that being under the bottom by .001" rarely creates a functional concern for a customer. In any case, I feel that the practice of using a 1 under hole size pin can lead to some customer concerns.
As far as a documented technique, I am not aware of any industry publications that address this. It is really left up to individual preference how to check it. But remember, whatever method you choose, you may have to justify your logic for that method at some point in time.
Ed Cosper
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From: [log in to unmask][SMTP:[log in to unmask]]
Sent: Tuesday, August 12, 1997 4:22 PM
To: [log in to unmask]
Subject: [TECHNET] how to pin gauge holes?
PCB Suppliers,
Continental Circuits (PHX) generally pin gauges holes to determine the
actual size. Our SOP has been to use a pin
.001 smaller than the bottom of the tolerance. That is, for a .043
+/-.003 hole we would use a .039 pin. If this passes through
with normal pressure, we say the hole is at least .040 and is in
tolerance. I can't find this technique documented anywhere and have a
customer who disagrees. They use the same size pin as the bottom of
the tolerance.
How do you measure holes? I could use some support for our method.
Rich Olsen
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Richard Olsen Telephone (602)-232-9154
Continental Circuits Corp. Main (602)-268-3461
3502 East Roeser Road Fax (602)-268-0208
Phoenix Arizona Pager (602)-310-6245
85040-2905 Internet [log in to unmask]
USA I make circuit boards,what do you do?
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