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July 2006

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Subject:
From:
Bob Wilson <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bob Wilson <[log in to unmask]>
Date:
Mon, 10 Jul 2006 08:46:51 -0700
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text/plain (92 lines)
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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