Cutting a larger circle on center of a smaller circle

Question

At work, we cut a 6" hole in the wall for a duct. Later we decided we now want a 10 inch duct in the same place. what tricks are there to center the larger hole over the center of the smaller hole if it is already cut? I'm using a hand saw to cut into dry wall.

score 3 · Answer 1 · edited May 18 '19 at 22:41

You can take a scrap piece of wood (maybe a scrap piece of drywall might work) and use the 10" hole saw to make a hole in the scrap piece (this will be your guide). Then center the guide onto your wall and use the 10" hole as a guide for the hole saw to keep it centered. It might be easier with two people, one holding the guide and the other using the drill.

you can see what I'm trying to say at around the 4:30 mark of this video.

score 1 · Answer 2 · answered May 17 '19 at 22:10

1

Use a couple of steel straps or bars with a hole at the centre clamped or screwed and re-mark and drill...

answered May 17 '19 at 22:10

Solar Mike

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the "center" is void space right now – Ryan May 17 '19 at 22:12
That’s what the bars are for... – Solar Mike May 17 '19 at 22:14

score 1 · Answer 3 · answered May 19 '19 at 17:58

If the first hole is neat, you can just take some calipers and set them to 2in, then scratch them around in a circle following the edge of the first hole and extending out radially. Not the most accurate method, but fast and will give decent results.

Cutting a larger circle on center of a smaller circle

3 Answers3