Following others on the "tip of the week".
Put down the disposable hole saw manufactured for a one or at best two times through sheet metal. We purchased a set of Greenlee 7238SB Slug Buster knockout punch set with 6 different hole sizes.
These are useful for two types of shops:
1- original. If your replacing a panel that does not come with a hole that should be there, you can get it very close and grind the last out with less time than using that silly one time hole gnawing thing that was manufactured for wood.
2- modified. We use these to pull wiring through places that were never there but should have been. When rewiring for fuel injection or something radical, we cut holes with these in 15% of the time it took before. The mess is 10% of what it was and the holes are Spot On!!!
Original use: Conduit.
Problem? Conduit sizes are kind of like NPT. It measures the inner hole, NOT the hole size cut. That said, some of the standard size rubber grommets can be found to fill. For instance- MGB firewall wiring plugs or best- MGB gearbox fill plugs (in body behind radio council) are teh perfect fit for one of the larger sizes and allow you to pull a large plug through a hole such as a computer harness plug which we do often. "It even looks professional"
Actual hole cut sizes according to my measurements:
0.885"
1.117"
1.360"
1.70"
1.95"
2.41"
One of my guys kept twisting my arm until we purchased one off evilbay. Instead of $350 new, a used set was less than $120 shipped. Best money I have spent this year on a tool! Worth the $350 but I'm cheap. Already used on 1 project 5 times. Hmm. Didn't use 3 size hole saws up. Didn't leave those horrible metal shavings. As they say- No brainer.
The other guys have used the set for a number of projects around the shop as well. If you have to rebuild or fabricate anything in your shop, you need these.
Worried about warpage? I have no or little warpage. I worry more about warpage and run out on hole saws!
If you want a demonstration of what a Greenlee does, check this video out and fast forward it to 3.30:
(from 3.30 to 6.00 for them to drill/punch)
http://www.youtube.com/watch?v=NX3YbhRrOvM-Brian.