Tim Wescott wrote in news:htydndfv-
:

On Tue, 11 Oct 2011 17:33:45 -0400, BQ340 wrote:

On 10/11/2011 5:02 PM, Tim Wescott wrote:
What size hole should I specify be drilled in Nylon to get a press
fit
for a 0.195 inch part? And what sort of tolerance range would I
need?
I want anything between a really light press fit that just makes
enough
contact to positively locate the part from side to side with no force
on it, to a press fit that requires maybe ten pounds of force (i.e.,
that won't break anything on assembly).

For that matter, if you specify a hole size in something like nylon
that tends to spring back, are you specifying the size of drill (and
expecting an undersized hole), or are you specifying the holes size
(and expecting the shop to compensate for the material)?

Here's the part: http://www.fairchildsemi.com/ds/QE/QED123.pdf.

This is probably going to boil down to giving the machine shop a
sample
or two and saying "Make work. Make work good". But I'm curious...



That part lists a +/- 10 thou tolerance on it's diameter, so it's
going
to be very hard to get a consistent press-fit.

Most light press fits are 1/4 to 1/2 thou.

The drawing would spec a hole size & the machinist would use their own
judgement & the spec'ed tolerance to determine if he can drill, ream
or
bore to hold the spec.

In my experience a press fit into pliable plastics like nylon is much
easier to achieve that into metal, and can have a lot more interference
than 1/2 thou.

It's the other side of the "hard to get an accurate hole" coin.

A lot of parts designed to be press fit into plastic are knurled, which
gives a bit more leeway.

Doug White