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Check out Youtube for pro demonstrations. You can drill like RJ said or even punch a hole with a screwdriver and hammer. The advantage of the punch is you don't leave shavings in the duct.

I'm not a pro.....just have spent a lot of time on HVAC ductwork project this year.
 

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3/4" unibit or holesaw. Make sure you DO NOT drill into the AC coil if you have one.:vs_mad:

Or you can do the Fred Flintstone and whack a straight screwdriver in with a hammer sideways like a knife.

I usually use a scratch awl and enlarge the hole by twisting sideways a bunch.
 

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Personally, I use a drill and don’t worry about the shavings. But if you want professional results you can’t leave metal shavings in the duct.
The best advice came from Yuri….don’t drill or punch into things you shouldn’t. It would make for a very bad and expensive day!
 

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Shavings aren't really a big deal. If the unit is off, you can collect the majority after you cut the larger hole for the collar if it really bothers you. My preference between the 2 is whatever is more handy at the time. Drill is less noisy. Both are quick.

There's a special tool for round collars, but it's not worth buying to do just one.

Cheers!
 

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It was a screwdriver at about a 45° angle whacked with the side of a hammer for me followed with L or R snips because that's how my mentor did it. That was before angle grinders were invented and lectricity was just a new kid on the block.
 

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It was a screwdriver at about a 45° angle whacked with the side of a hammer for me followed with L or R snips because that's how my mentor did it. That was before angle grinders were invented and lectricity was just a new kid on the block.
Were the dinosaurs also still around? Lol JK.
Angle grinders don't do a great job on round holes, especially for spin-ons. I do use them for spiral ducts though, they usually use fairly thick gauge.

Cheers!
 
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