by H. D. Candland
I thought you might be interested in this….
While working on a project, I needed to draw a fairly large circle (approximately 8-10 inches in diameter) on aluminum plate. Due to the size of the circle, I did not have anything in my toolbox that would allow me to draw this circle. I do have a machinist’s compass from many years ago, but could not reach this dimension. The gimmick shown in the drawing was my answer to this problem.
Someone wishing to make this compass just needs two small scrap blocks. I used aluminum for mine but just about anything would work. After drilling the 3/8″-diameter holes, I drilled the marker hole to .413″ to fit the Helix marker that I used. Four 10-24 screws, 1/2″ long, were used to clamp the blocks to the steel rod and also clamp the marker and pivot in place. I hope this helps someone out.