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
