This is a customizable fourth axis for a CNC with the following design goals:

-Low profile for stability and for CNC’s with limited Z travel
-Handle small stock
-Use as much of the stock the as possible with small jaws
-Glue on disposable jaws for stability and grip
-Mostly printable with few extra parts (Nema17, 2xbearings, GT2 belt and pulley)

This project uses the pulley designed by droftarts thing:16627.

The idea is that you print the small jaws for every stock you need to mill, and glue them on at both ends.
You can customize these to fit your stock in round or rectangular shape. There is also a jaw that goes 2mm into the stock, if your stock has an irregular shape.

On top of each buffer there is a slit for aligning your endmill.

At the end of one of the buffers, there is a ramp, which has the same height as the center of the stock.

https://www.youtube.com/watch?v=5Zt0ztJfinw
(In the video you can see the stock moving slightly up and down, That's because the end of the stock was not cut precisely perpendicular to the longitudinal axis)

https://youtu.be/SHa2YowvOmQ
(In this video the belt was too loose, the belt needed a bit of breaking in)

If you need software, have a look at Leo69's: http://www.thingiverse.com/thing:1877336

Make sure you first layer is not squeezed out when you print the gears and jaws. If it is, then the star will not grip properly.

Print the gear with one outer layer, to get the most detail in the gear.

The rest is not sensitive to print settings.