Modeled after precision drafting compasses, this 3D printable one prints as a single piece, pre-assembled! It uses a standard 6-sided pencil.
For best results, set your line width to 0.4mm and print slowly.
UPDATE: I've made the bow spring at the top a little less stiff. (You should preview your g-code to make sure this spring section is printed solid.) I also made it so that the center fulcrum piece won't come loose if the compass is all the way open.
Remove the support material carefully. You'll need to pick it out of the nooks and crannies with a pointy tool or x-acto knife. Then, gently grab the adjuster screw with some small pliers and twist it back & forth slightly to break it free from the pivots. Once free, run the screw back & forth until it operates smoothly. Insert about a 1 1/2" length of pencil and start drafting!