Re: gEDA-user: gEDA mounting hole for screws

[Dan McMahill <dan@xxxxxxxxxxxx>]

DJ Delorie wrote:
> > 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.

I typically use a 0.125" hole and 4-40 machine screws.  Never had a 
problem with that recipe.

Don't forget that the "slop factor" you need for mechanical mounting 
holes will depend on quite a few things.  Are you having a chassis 
machined?  Are you drilling mounting holes in a box yourself?  These 
questions will start you on the path to finding out how much 
misalignment you may get between standoffs and your holes on your board.

-Dan