I needed a very enormous compass and could not find what I wanted so here is one if anyone else is in need of one. This uses 1/2" square stock of any material and length. I used cherry wood but aluminum works just as well. Has a ball bearing pressed into the base and uses a round pencil (7.25 mm). This design has raised lines to make alignment and measuring easier. Uses (4) #2x56 bolts 3/4" in length. The ball bearing is 11 mm. OD with 5 mm. ID and is 4 mm thick. Might put some dycem on the bottom of the cone if slippage is a problem.
Only the end pieces need rafts the round base does not...