This is an easy project that anyone can make with just a few tools. To make it I used a nut, 2 bolts and a small nail. It can make circles 1/2" to 7".
Check out the video
One end of the threaded rod is tapered using a belt sander. This was done by eye, just slowly sanding while checking for evenness.This is the end that the pencil will sit in.
The end was center punched and ready for drilling.
I like to use small bits and work up to the right size I need to fit a pencil.
The nut was center punched on both sides. One side is for the pin while the other side is for the 1/4" thumbscrew.
CA glue or crazy glue is used to hold the nail in place.
Complete. It adjusts very quick and the set screw makes it easy to lock in to whatever size you need. Fits in your pocket or hang it on the wall, either way this tool is one I will keep near by.