My engineering beam compasses can't accept a Sharpie. I've had a set of woodworkers' trammel points for a long time so I dug out some of the evil brown stuff and made a REALLY BIG beam compass...
To allow the beam to accept markers of different diameters, I copied the arrangement that Elmer Verburg used on the smaller beam compass I built...
Tools by Elmer Verburg
A simple V was bandsawed into the end of the beam. Then a small hose clamp through a transverse hole was used to clamp the marker into the V. The adjustability of the hose clamp means it can accept many cylindrical sizes, including center punches for marking out points on a radius.
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