Punching holes

[Martin Pansch]

Does anyone have a rule of thumb they use for when to punch a hole from just one side versus both?

Punching thicker stuff, maybe 1/2" or thicker, I start it on one side, drive it most the way through (three hits, cool and/or lube the punch, three more hits, repeat until the resistance indicates getting near the anvil) then flip it over, line up with the dark, smooth spot, and drive through from there letting the material be the bolster for the most part.

When I do thin hinges, maybe 1/8 thick material or so, I'll just punch through all from one side. It is so thin it is usually just two whacks on the anvil, then move to the bolster plate and one more hit will put it through.

Both give me pretty clean hole. I am not sure of the optimal technique for stock between those thicknesses. While slot punching bottle openers recently, about 1/4" thick, I was flipping them to finish the hole and found I was leaving a lot of rag. It could be that my slotted bolster block wasn't as close of tolerance as it should have been to get a good shearing action but I am wondering if it wouldn't have just been better to go all the way through from one side. I understand from Mark Asprey's book that doing that leave more material on one side of the hole than the other but in this case processes after the punching would have made that a moot point.

Guessing someone with a more organized mind than mine already figured out the optimum.