Re: gEDA-user: gEDA mounting hole for screws

[DJ Delorie <dj@xxxxxxxxxxx>]

> Just a random question for the anybody:  For, say, an 1/8"
> through-hole, what kind of tolerance factor do you add for safety?  I
> make my 1/8" holes 0.127", but 0.002" seems kinda tight.  What's the
> recommended slop factor for mechanical mounting holes? 

Searching for "machine screw clearance hole size" results in pages
like this one: http://cfa-www.harvard.edu/~masermri/screws/screw2.html

A #5 screw is 1/8 actual diameter; they recommend 0.129 - 0.136 hole
size, for example.  That's 4-11 thou over.

This is based on woodworking experience, but I go up 1/64 (15 thou)
when drilling the "loose" side holes.  So, 9/64 for a 1/8 actual
screw.  Try measuring your screws some day; they're a tad undersized
anyway, since normal drill bits aren't available in thou increments.

If you think this is a lot, measure the actual hole size of standard
steel washers vs the diameter of the screws they match.  I usually end
up buying the next size smaller washer (1/4 washer for 5/16 bolt) at
the hardware store; they usually fit nice and snug (I check them).