And speaking of tapping, how close to an edge can I tap?
There's been a few times where I've drilled a hole close to an edge, tapped, it, and had the threads swell the edge by the hole. Is there some standard for how much meat should be allowed so that this doesn't happen? Is the necessary distance different for different materials?
I think the rule is whatever is strong enough to do the job the part is intended to do. Seriously. I have seen some threaded holes for special applications where the side of the hole is just plane missing.
I've tapped 3/8-16 into 3/8" bar edge-on, for practice, and the parts looked good when the holes were exactly centered. But there was so little leeway for error that I dropped back to 1/4-20 for the real parts used to make a metal frame.
That's a reasonable rule. Of course, if you produce the edge after the tapped hole you can go closer.
IIRC I found I could get away with an 0.030" wall outside a #2 or #4 tapped hole in 6061 aluminum. There was some difference between a cutting and forming tap, but not much.
The application was prototype RF-tight aircraft radio enclosures and the electrical engineers didn't take notice if the threads printed through slightly.
I probably should have left clearance for a Helicoil, but I could drill stripped holes deeper and mark them for longer screws.
jsw
Re-cut the edge of the part after tapping.....
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