On Oct 11, 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...

--www.wescottdesign.com

If you make the hole any larger than 0.185, LEDs at the small end of
the tolerance will not be a press fit at all. What you may want to do
is drill the hole a tad smaller than .185 +0/-1 (and you ALWAYS want
to specify a finished hole size) and then see how it is to press in
something 0.205 diameter. My guess is that it's going to be too tight.

Your choices may be to buy and measure a batch of LEDs (they probably
won't vary much in a single batch) and drill the hole to suit, or, use
some sort of adhesive. Another option would be a small printed circuit
board to hold the LED and a screw to hold that to the plastic.