FreeLists / pcdlist / [pcdlist] Re: Thru hole components

[DUTTON Phil <phil.dutton@xxxxxxxxx>]

Hello Bill,

You are completely correct.
No point specifying hole sizes in increments smaller than the tolerance on
the actual holes.
+/-0.05mm (0.002")is fairly typical of most manufacturers' everyday
capabilities. (your 0.003" is fine)
I believe that the drills are sized in 0.005mm increments as well. (metric
series - imperial may be in the 0.003" increments that you mention)
So size your holes based on your best judgement. Don't forget that machine
placed through-hole components may need a slightly more generous hole to
accomondate the placement tolerance as well.
Don't worry about the differences in metric and imperial tolerances - same
thing, just measured in different units.
I usually use the level B recommendations in IPC-2221 and minimise the
number of different drill sizes.
This limits the number of drill changes on the NC drill machine as well.
(excessive drill changes slows down the drilling operation.)
As another post mentions, press fit holes need to be toleranced to suit the
component manufacturer's recommendations.
I hope this helps.

regards,

Phil.

Phil Dutton C.I.D.
Senior CAD Technician
IPC Certified Interconnect Designer

Tenix Defence Pty Ltd 
Electronic Systems Division
Second Avenue, Technology Park,
Mawson Lakes.  SOUTH AUSTRALIA  5095




-----Original Message-----
From: Watt, William (sys) USX [mailto:wwatt@xxxxxxxx]
Sent: Friday, 10 May 2002 02:46
To: 'pcdlist@xxxxxxxxxxxxx'
Subject: [pcdlist] Thru hole components



Now that I know there are a few people out there, let me ask a question.  We
are having a discussion here in our design dept about standardizing hole
sizes.  The present method of determining finished hole size is to use the
IPC 2221 formula and pick the hole in the center of the range.  This is fine
except we end up with many holes that are within .001 of each other and our
mechanical checker or the fab house will ask to combine them into one common
size.  I recall from a past life that I used a hole chart with drill sizes
every .003 instead of every .001 and this worked fine.  I am having trouble
convincing some of my coworkers of the wisdom of this method.  I would like
to know if anyone else has an opinion on this. I would like to standardize
by using the formula, finding the median size and rounding up to the next
drill size.  How does the rest of the world do it?

Thanks for the help.  Maybe I can use an overwhelming opinion to convince my
department.

Bill Watt
Moog Inc
Jamison Rd
East Aurora, NY 14052
716-687-5596
wwatt@xxxxxxxx

To unsubscribe from the pcdlist, send an e-mail to
pcdlist-request@xxxxxxxxxxxxx with "unsubscribe" in the subject field.

If you have any questions or problems, contact tgentry@xxxxxxxxxxxxxxxxxx
To unsubscribe from the pcdlist, send an e-mail to 
pcdlist-request@xxxxxxxxxxxxx with "unsubscribe" in the subject field.

If you have any questions or problems, contact tgentry@xxxxxxxxxxxxxxxxxx