This is an attempt to summarize all my efforts to make a low cost 3D printed rotary axis for my MultiBot machine.  My machine is limited on its vertical height, so there is not much point in spending a lot of money on a quality spindle, but I still want to experiment with rotary axis. 

I started with a $15 2" chuck. 

After a lot of experimenting I settled in on a setup that could drive the chuck. As much as possible I relied on 3D printing, even the gears are printed.  

Next comes a low cost tailstock.  I ended up using a skateboard bearing and a 100 mm long M6 bolt to make the quill.  This works surprisingly well.

To finish off the hardware I cut a piece of MDF for the tailstock to ride in.  This is working really good.  I may tweak the design just a bit to tighten things up but for a pile of plastic and cheap hardware it is more than good enough.

The electronics took quite a lot of time to get sorted out, but in the end I ended up running GRBL-Mega-5x on a MKS GenL v2 board to get the 5th stepper motor driver.

My last hurdle is on the software side of things.  Using Fusion360 to make a round part is no problem, but trying to get CAM support for actually driving the rotary axis has been quite frustrating.  LightBurn works ok for the laser side of things, although it is rough and could use some polish to make rotaries a first class tool.  I'm still searching for a tool that is low cost or free that can drive the mill side of things.  I will keep at it and hopefully something clicks sooner or later.  Others have managed to make this work, so I know there is still hope.

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You can follow along with all the changes at the links below

https://hackaday.io/project/176110/log/195170-round-a-bout

https://hackaday.io/project/176110/log/195336-bear-down
https://hackaday.io/project/176110/log/195373-driven
https://hackaday.io/project/176110/log/195449-roto-rooter
https://hackaday.io/project/176110/log/197560-gyrations
https://hackaday.io/project/176110/log/197909-belt-drive
https://hackaday.io/project/176110/log/197914-wired-for-speed
https://hackaday.io/project/176110/log/197920-as-the-gear-turns
https://hackaday.io/project/176110/log/198205-spin
https://hackaday.io/project/176110/log/198399-tailstock
https://hackaday.io/project/176110/log/198461-progress
https://hackaday.io/project/176110/log/198493-winner
https://hackaday.io/project/176110/log/198629-slide-to-the-right
https://hackaday.io/project/176110/log/198779-brains
https://hackaday.io/project/176110/log/199447-slow-progress
https://hackaday.io/project/176110/log/200315-progress
https://hackaday.io/project/176110/log/200710-success
https://hackaday.io/project/176110/log/200711-firmware
https://hackaday.io/project/176110/log/200831-aarg
https://hackaday.io/project/176110/log/201338-spin-lock
https://hackaday.io/project/176110/log/201470-progress
https://hackaday.io/project/176110/log/202119-small-progress
https://hackaday.io/project/176110/log/202359-frustration
https://hackaday.io/project/176110/log/202366-hope