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Comments on How do I draw a perfect circle on a square of plywood?

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How do I draw a perfect circle on a square of plywood? Question

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I'm working on a string-art project on a 3-ft square of plywood. It will have brass nails in a circle with different colors of string connecting the nails in a pattern.

I'm trying to figure how I can draw large enough circle on the plywood. I've thought about:

  • Finding a bowl to trace, but none in my house are large enough.
  • Using a compass, but again, mine isn't large enough.
  • Freehand drawing the circle, but it comes out too imperfect.
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When I needed to cut a 4' circle out of the middle of a sheet of plywood, I fabricated a compass by tying a long-enough piece of non-stretchy string to a tack or finishing nail -- I forget which, but it was something small enough that it wouldn't leave a mark on the other side of the plywood.

To the other end of the string I tied a pencil at the desired radius. Working on the side of the plywood that I designated as the back, I found the center point by measuring, drove in the tack, had a friend hold it in place just in case, and walked around the board tracing the line with the pencil. Tip: do this at sawhorse or table height; you want to be able to walk around it and maintain consistent tension while doing so, not crawl around on the floor.

Measure twice, cut once: after I had a line I could see, I measured the diameter in a few places to convince myself that any variability was within the margin of error that cutting it out with a jigsaw would produce. (Maybe there were better ways to cut it, but a jigsaw is what I had.)

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2 comment threads

How did you ensure the pencil stayed straight? (2 comments)
Will this work for the front? (2 comments)
Will this work for the front?
Stephen Ostermiller‭ wrote over 1 year ago

In my case I need the circle on the front of the plywood because I'm not cutting it out. Is there a way to attach the center of the makeshift compass without making a mark in the center with a tack or nail?

Monica Cellio‭ wrote over 1 year ago

Oh, it's not a cutting line -- I read too much into your question, sorry. I don't have experience with a way that doesn't leave at least a small mark; I never experimented with tape, for instance. In that case the other answer is better than mine.