Hello Dennis,

The true position specification is simply the definition of a circular
tolerance zone where the theoretical center of your feature must reside.

In its simplest form, a .010 (diameter) zone callout, means that the
center-point of your feature will be able to move in any direction .005
from theoretical center.

So now, if the zone is decreased to dia .003 the feature's movement is
limited to .0015

This is the simple, short, viewed from 10,000ft answer.  Some other
posts will lead you to the info that 2 week classes are designed around.

-- Kelly Dack (IGT -- Reno, NV)



-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Denis Lefebvre
Sent: Tuesday, April 25, 2006 8:18 AM
To: [log in to unmask]
Subject: [DC] Diameter True Position

I must admit, this is a drawing callout that I have never fully
understood. Back in the early days, per MIL-STD-275 I'd callout Diameter
True position at 0.010", then at some point in time it was reduced to
0.008". Now I have someone telling me it should be 0.003". Huh?
 
Can someone help me understand what this (Diameter True Position) means
and how dropping the value to 0.003" might be a good thing or a bad
thing?
 
Denis Lefebvre, CID+
Sr. PCB Designer
Finisar Corp <http://www.finisar.com/index.php> 
(408) 542-3832
 

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