The compass prototype needed an improvement on its original non-slip tip, which was the eraser end of a "My First Ticonderoga" pencil. After a little digging at the local hardware store I came out with some rubber stoppers that I thought might work.
To fit the compass, the stopper had to be screwed to a short section of 3/8" dowel. I drilled a countersink just larger than the screw head, and then a smaller hole just larger than the shank all the way through the stopper. In the dowel, I drilled a pilot hole a little smaller than the shank.
I was worried the screw might split the dowel, but I guess I got the sizes right, as everything worked just like it should. Here's a picture of the final product.
![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjz9sCmktO5LAygN7pirSTmce7hsfcRr9VTdEc8XglMcUdJ3Efl2RET3ORRdevTZeRqiBtwQlbsUiRU61QdFp7njPwHEHex29MilNpXlafBf4g2Leh9FF_jiR4VW4MXwJzl0566aBWaZPc/s400/Compass+Protoype+3.jpg)
You can also see the plowed guide channel for the wedge that tightens the chalk side of the compass. The dowel with the rubber tip is just a friction fit.
I tried it out last week and it works much better. It will still slip if there is a lot of chalk on the board. Or if my technique is sloppy...