Here is a useful tool for turners – a giant pair of homemade compasses. When preparing large bowl blanks the usual commercial compasses may be too small. I made a large pair from scrap wood. Opened to 90 degrees, they can make a circle of 800 mm radius. You could make them any size you like.
My pair has arms about 550 mm long, made of planed scrap softwood. They are joined at the top by a small coach bolt, washer and wingnut. One arm has a pointed nail inserted, the other has a simple clamp to hold a pencil. Drill the hole for the coach bolt the same diameter as the bolt. The square part of the shank will pull into the hole when you tighten the wingnut, and stop the bolt turning.
To insert the nail, drill a small hole in the end of the arm. The hole should be just a little less in diameter than the nail, to stop it splitting the wood. Cut off the head of the nail and grip it point down in a vise, then tap the arm down onto the blunt end. Cut the arm to a blunt point so the corners don’t get in the way.
The pencil clamp
To make the pencil clamp, drill a hole for the pencil first, making it a sliding fit. I shaped the end of the pencil arm a bit, but that isn’t essential. I just thought it would look better that way. But a blind hole for the pencil might make it less convenient to adjust. Then drill a cross hole, close to the pencil hole but not intersecting it. Now make a saw cut to split the pencil hole down its middle. Go a bit past the cross hole so there is some spring in the wood. Fit a small coach bolt, washer and wingnut in the cross hole. When tightened, it will close the saw cut and pinch the pencil to stop it moving.
Smooth off any rough edges, drill a hole through both arms near the pivot so you can hang it up, sharpen the pencil, and your homemade compasses are finished.