Spring Loaded Sharpie Holder for CNC Machine

I designed this holder so that I could trace the outline of a part and check clamp clearance on a CNC Mill. I didn't like the idea of using a balloon as a spring and wanted to design something that was mostly 3D printable. 

The top has a ½" shank to fit into ½" collets. 

I do not have a part number on the springs that I used as they were just ones I had lying around. The springs that I used were 1.75" long, but were very thin so I stuck 2 inside each other to get the pressure that I wanted. 

It's been a while since I printed this, but I believe that I used 100% infill for shank strength and I printed in the same orientation as the 2nd picture.