> 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).
