Pen holder for CNC

Pen holder for a home/hobby CNC. This thing is designed to be used with two 1/4-20 bolts. One screws in from the flat side and is chucked into the router's 1/4" collet. The other is used to lock in the pen or pencil. Neither of the holes are designed with threads inside. I printed at 60% infill so it wouldn't flex while drawing and there would be plenty of material for the bolts to cut threads into.

Set the pen so it looks like the tip is in line with the spindle center. Lower the Z axis until the tip touches a piece of paper. Rotate the spindle/collet 360 degrees. If the pen draws a circle, it needs to be adjusted. If it stays in one spot and just makes a dot, you have it set correctly.

The pen slot is sized based on a standard Sharpie Permanent Marker, with about an extra millimeter of radius for slightly larger pens. The side opposite the set screw is tapered to a point to accept smaller diameter pens too.