I tried my make of this thing (finally) and had a couple of problems:
Note the bottom ball race will be trashed / seized by the swarf from the cutter. Need fully sealed bearings.
The clearance hole for the bolt needs to have clearance! Suggest making the bolt hole in the tool 10 or 12 mm to give good clearance. this would solve 4 below too.
The cutting action pulls the bolt downward, pressing the head into the non moving plastic surface. Suggest a design where the top bearings top surface is exposed, and acts as spinning platform for the bolt head.
There is no clearance behind the hob. The hob is rough when cut so the bolt tends to stick on the tool. Suggest need a bit of clearance.
hope that helps someone.