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3 3/4" in 18ga sheet metal

1K views 3 replies 3 participants last post by  mustangsal 
#1 ·
I'm trying to cut a hole for a speedo in a piece of 18ga sheet metal. I have a hole saw, but it says it should be used in a drill press and not to exceed 500rpm.
I tried with a hole saw in an electric drill. It didn't work out so well. As soon as the teeth touched, it jumped and chattered.

The slowest I can get my drill press is 750 RPM.
How much of an issue will this be?
Do I look for an alternative?
 
#2 ·
I hope its not a plain carbon steel holesaw as you will probably just flatten the teeth trying to cut a hole in steel. You’ll need a bi-metal holesaw.
I’ve had luck by using the holesaw as a guide for the ¼” drill bit in its center after locating the saw where I want it. Then get a piece of approx. ¼” plywood and drill a ¼” hole in it. Place the plywood over the sheetmetal and locate it using the drill bit shank like a dowel so that both ¼” holes line up, then clamp the plywood and sheet metal together. Start cutting a hole in the plywood using the pre-drilled hole as a guide. You can even put a piece of ¼” stock in the holesaw instead of the drill bit to keep from messing up the ¼” guide hole. After the wood is cut through remove the wood from inside the holesaw then start cutting through the sheetmetal and the hole in the wood will help hold the saw in place like a pilot hole. You may want to use thicker plywood or even a 1x6 instead.
FWIW
ssmonty
 
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