+/-.001 on a plated hole? I do not think that is feasible. Pressfit
backplanes are +/-.002-that is about the limit.

At 02:59 PM 12/02/2005, you wrote:
>Hi John,
>
>Standard machine shop drill tolerance is +/-.003, but you can
>realistically get down to +/-.001 on FR-4.  Actually, the tolerance is
>+0,-.001 of the bit size unless the shop runs their bits so long the
>diameter of the bit gets smaller, in which case, you might get -.002.
>There is not an infinite gradient of bit sizes, and more importantly,
>shops overseas use metric, so choose your hole size carefully.  The
>shops might complain, but we've been getting boards, (and measure hole
>size on every shipment), using a spec of +/-.001 for 10 years or more.
>Unfortunately, our tooling hole size is inch, so our metric board shops
>have to order custom drill bits to match because of the tight tolerance.
>
>(I've tried getting the board shops some more tolerance, or at least a
>change to metric hole size, but SMT manufacturing did want to change
>tooling pin sizes or allow extra slop between the tooling pin and hole.
>:(
>
>Regards,
>Ryan
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Babcock John
>Sent: Friday, December 02, 2005 2:32 PM
>To: [log in to unmask]
>Subject: [TN] Drill Tolerances
>
>We've had problems with this in the past so maybe the group can help me
>out.
>
>I have a mill-max receptacle pin with a .040 diameter.  The datasheet
>calls for a .042 minimum dia. plated through hole.
>
>Is it better to call out a .048 hole with a +/- .003 drill tolerance?
>(because if you stack the .003 positional tolerance as well, you could
>get down to the min. .042 hole).
>Or is it better to call out a .047 hole with a +/- .002 drill tolerance?
>(because with the .003 positional tolerance you could get down to the
>min. .042 hole).
>
>Or does this depend on which board house you go to as well?
>
>John
>
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