I started another thread to ask a question in the PCB milling forum however I think my testing deserves it's own thread over here.
I was working on a dedicated mill for doing PCBs and I was looking at interesting ways to design the Z axis. after looking through a whole bunch of interesting designs (rep rap wally) I found the build thread for the Swiss Mak. I saw that he planned to use acetal/delrin on aluminum and had settled on box ways over dovetail ways. It wasn't something I had considered and the more I thought about it the more interested I became. Unfortunately I can't seem to find much information on how to design something like this and I started to do some experiments.
My requirements are milling PCB's at between 12k and 30k rpm mostly with a 500w spindle and .8mm end mills. The work area will be 200x200x30mm. typically the machine will not need to move the Z axis more than 3 mm when milling.
Here are my results so far and they are much much better than what I could expect from what you typically see in a pcb mill (8mm unsupported rails).
https://youtu.be/PIIW-9bG6eo