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Date: | Mon, 10 Jul 2006 08:46:51 -0700 |
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That is precisely what the geometric statement means: "...position tolerance
within a circle." It reduces scrap and part rejection if it is done
right.
It allows for a bonus tolerance over the bilateral (square) tolerance zone.
A square zone is limited. A circle has more area where the center of the
drill is allowed.
One thing that is missing is the tolerance applies to a Maximum Material
Condition. The statement should have a circle with an "M" inside. And it
usually, but not always, has a tertiary datum specified.
There are a few places to get good books on this.
One is http://www.engineersedge.com/GDT_Training.htm
Regards
Bob Wilson CID
Electro-Mechanical Designer
SpectraSensors, Inc.
972 N. Amelia Ave.
San Dimas, CA 91773
800-619-2861 x239
www.spectrasensors.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Donald Kyle
Sent: Monday, July 10, 2006 8:10 AM
To: [log in to unmask]
Subject: [TN] Geometric Tolerance
We are having a little debate here as to the interpretation of a Geometric
statement evolving the tolerance of holes on a PCB.
The geometric statement reads from left to right:
Position (symbol)
Diameter (symbol)
.005 (tolerance)
X (datum)
Y (datum)
Some say that this statement means a positional tolerance zone within a
circle.
Others say that this is just another way of stating a bilateral tolerance
zone within a square.
How do you interpret this?
If you have IPC-D-325A you can read about this on page 28 and appendix B for
more information.
Because I don't know how to insert a geometric symbol for POSITION and
DIAMETER you will need to use your imagination here.
Geometric Geometric Tolerance Datum
Symbol for Symbol for Reference
Position Diameter
__ __ .005 X Y
Thanks for your time
Donald Kyle C.I.D.+
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