There are a couple of drawbacks when using hole saw attachments. You risk twisting or warping some metal panels. You also have to deburr the jagged edge with a hand file. The alternative is using a knock-out punch. I use a Greenlee part # 730EBB-120 cutting blade.

Last time we inquired about the price, they were around $450 in the states + Large 3/4″ socket wrench, and 2″ socket. We wouldn’t use anything less than 19″ long socket wrench. Estimated purchase price of $550 new for everything needed. Fortunately we could write off the high cost as a business expense, but you can periodically find used knock-out punches on Ebay.

The Greenlee’s circular blade cuts through the steel as you tighten the socket with the wrench.

Example of hole made by Greenlee knock-out punch. Clean, no deburring necessary.