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Just saw an article on Popular Mechanics about sheet metal. They maintained that you should always expand drilled holes via several bits.
I can see that you would do that with the Unibit because it has all of those steps. However, for what little I've ever done, I've used just a pilot followed by the final bit, or skipped the pilot if the hole was small enough.
Experienced sheet metal guys please respond with criticism and abuse for my primitive technique
They did point out something interesting. They described using an adjustable radius hole saw, and mentioned that since it was unbalanced, it could be quite dangerous. I hadn't known that anyone would use one of those on sheet metal, and that would seem to be a good reason not to.
Unibits are definitely the way to go, they expand it slowly with a single bit, but if I do not have one available, my next choice is a pilot hole and a hole saw. I know it is overdoing it, but when working with very thin sheet metal I find it doesn't rip it up as much as a other bits that I have in my house. Also, just for a final note, I have not used a hole saw many times on sheet metal, just when I couldn't find something more suitable.
Sounds like they are taking something simple and making a big production out of it. I have always just drilled with the bit in need and if the metal bends I just straighten it back out with a hammer, and run the bit back through it.
Unibits work great. They avoid the "three-lobed hole" problem with regular twist bits in thin metal. Takes some time to get the first step through (in steel, especially), but after that, they step up size by size in seconds.
Using larger bits in one shot can grab the metal and either break the bit or trash the area around the hole. Unibits are good for sheet metal work, as are regular holesaws.