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

[Tom Colby <tcolby@xxxxxxxxxxxx>]

With the myriad of drill sizes in both inch and metric, I've found this to 
be a daunting task.

Here's what I've settled on.

All footprints are built according to the data sheets and common formulas 
to determine the drill size.

All of the sizes in my drill chart are defined with a tolerance, for instance:

a 1/4 resistor could be .035 +.003/-.002 DIA AFTER PLATING
a diode could be .037 +.003/-.002 DIA AFTER PLATING

When I'm ready to post process the job to produce gerbers and drawings, I 
review all drill sizes and combine sizes that fall within the tolerances of 
others. In the case above, I would modify all of the 1/4 resistors to use a 
.037 drill and then post process the job.

It may not be the best solution, but it works for me. I'd be interested in 
any alternative methods.

Tom


At 01:16 PM 5/9/2002 -0400, you wrote:

>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
>
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