Need Help Measuring Radius

[Paul Page]

I'm making a cherry frame for a mirror that is shaped like a half moon. I'm making a MDF template and have the inside of the arc cut. My question is how to measure the outside of the arc so that the frame maintains the same width along the entire frame?

Thanks,

Paul

[Paul Atkins]

Use a compass or trammel. How did you get your original arc? Use the same center point.

[John Coloccia]

I'm making a cherry frame for a mirror that is shaped like a half moon. I'm making a MDF template and have the inside of the arc cut. My question is how to measure the outside of the arc so that the frame maintains the same width along the entire frame?

Thanks,

Paul

If you hadn't already cut part of the template I would have recommended making a quick template out of cardboard first that represents the inside of the arc, i.e. the outside of the template would fit inside the finished piece. Then I'd tape that to my MDF and mark it. Then I'd come back with a washer, stick my pencil in the hole, and mark around for the outside of the arc using the washer as a guide against the cardboard template. Does that make sense?

You can use a compass as Paul suggests, but you need to be sure to keep it exactly normal to the surface of the arc or you will get thickness variations. personally, this is probably what I would do. You can still do the washer thing, though, if you're not confident to can scribe precisely. You simply need to use some heavy paper to act as a fence along the inside of the arc. Tape the paper to the arc, and mark with the washer along that.

[Dan West02]

I would just cut a triangle out of a piece of scrap. Use a nail or a dowel near two of the corners. These will ride along the inside arc. Then cut the scrap so that it projects past the inside arc the distance that you want between the inside and outside arcs.

If this is not clear, PM me with the size of the inside arc and the distance you want between the inside and outside arcs. I will lay it out in cad and send you a PDF if you include your e-mail address.

[Paul Page]

Thanks, Dan. I was able to follow it and it worked fine.

Paul