Cutting a round hole in ductwork - GIF

Cutting a round hole in ductwork.

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Previously:

https://www.homemadetools.net/forum/...602#post178131
https://www.homemadetools.net/forum/...168#post161153
https://www.homemadetools.net/forum/...539#post177998
https://www.homemadetools.net/forum/...886#post175498
https://www.homemadetools.net/forum/...502#post151237

Is that actually a circle though? At 90 degrees if you project a circle onto a cylinder it approximates an ellipse (if you unroll the cylinder's surface). Other angles make egg shapes. You can probably jam it in there because it's just ducting, but for materials more rigid than dirty old tin this method won't work.

This is a neat website. Give it some parameters and it'll spit out a printable PDF template you can use to cut your pipe.

https://cq.cx/tubejoin.pl

That type of nibbler makes some nasty, sharp crescent shaped swarf.....Hate that stuff!

Talked to a guy at a sheet metal shop; he said those were known as meat-hooks!