I really like the 4th axis I purchased a few years back, but when I went looking for it again the suppliers who once carried it no longer do. Anyone know who makes it? Center hole receives collets. I own a ShopSmith so I am using a 5/8th rod and can mount it's chucks onto this machine. Also I like the use of the skateboard wheels, they are adjustable and one could use more sets over a longer axis. The Sherline z-axis is not my first choice, I just had a spare.