Quote Originally Posted by pmesilver View Post
ideas from the forum to build a 4th axis for my mill.
You can build something like this -

https://www.ebay.co.uk/itm/Hollow-Sh...cAAOSwY3BZGmIp

Use an ER collet chuck on a straight shank, stepper of your choice, step pulleys of your choice for drive ratio, steel cored belt for minimum stretch and re-design the eBay offering with a plate and bearings outboard at the back behind the belt to take the flex load off all the components and convert it to compression load.
Shout f you want more detail,

- Nick