Cut a 1" round hole in galv duct?

[dean]

Sounds simple - how do I cut a neat 1" round hole into hot air duct? Its flimsy and I can't get behind it easily. I don't have an air nibler either, and would rather not buy one if possible.

Thanks!

Dean

[RicodJour]

Bi-metal hole saw.

R

[Bennett Price]

[Bob]

Borrow or rent a knockout punch tool. The kind used for electrical work. Greenlee makes one.

[hallerb]

why do you want the hole?

drill a ring of 1/8 inch holes in a circle and use the drill or a dremel tool to finish it.

[Joseph Meehan]

I would (and have) cheap hand nibbler from Radio Shack.

[Doug Kanter]

That assumes he can get his hand inside the duct.

[Doug Kanter]

Use a 1" hole saw. Here's a (lousy) picture of one:

If the link's broken, go to and search for "hole saw". You also need an arbor. The arbor holds a 1/4" pilot bit which sticks out maybe

1/2" ahead of the cylindrical hole saw. The whole setup will cost you about $25. If you get the right arbor, it'll be usable with a variety of hole saw sizes.

[Bob]

I just assumed that he was going to put something through the hole, but you're right.

[hallerb]

I was concerned he might be planning to put a electrical cable in the duct, a bad idea.

[dean]

It was for a thermostat probe on a wood furnace. I drilled a small hole and then enlarged it with an irwin unibit. It was perfect!

(Sorry, I forgot I had that drill!)

Dean

[Doug Kanter]

Those Greenlee punches are really cool, though. :-)

[Doug Kanter]

Picky picky picky. What's so bad about putting a wire through a sharp-edged hole, into an environment where it might be at least dried out by heat, or maybe melted? You worry too much. :-)