Heres a quick print to make hobbing bolts easy. It clamps into a stock taig tool holder and works with 608 bearings. I've used it to hob bolts for both a Mendel 90 as well as an Orca.
My cutout for the tap to clear the mount is slightly off centre (I blame it on witchcraft) but it functions perfectly none the less.
Keep the plastic mount firmly against the tool holder to minimize vibration when cutting. The cutting axis is centred on the tool holders edge so the 2 small set screws (on the tool holder) only need to hold the mount from twisting.
This could probably be printed without support if your orientate it correctly but I printed it sideways with support to get the strongest "grain" direction of the plastic.
Printed in PLA at 0.2mm layer with 2 shells and 20% infill, seems more then strong enough.
I've found that an M8 tap makes for some nice clean teeth. Stop advancing the cut once the valley of the tap makes contact with the bolt shaft. My old hobbed bolts had a much larger valley for the filament to rest which seems to strip plastic far easier then nice flat cut teeth.
I've used washers to fine adjust the height of the bolt for hobbing, recently I have clamped the whole works into my milling attachment for the lathe and used the vertical feed to get the alignment perfect.
The tap will auto advance the cut but helping the bolt spin off the start will result in cleaner cut teeth. Keep the cut light until you establish linearly spaced teeth, I found that after the teeth spacing is prefect a heavy feed results in cleaner cuts.