Hi Hood,
The worm is on an eccentric, and is easilly adjustable (its the bronze coloured ring to the left).
Worm also has a thrust race that is preloaded and the eccentric has a clamp collar to remove just about all the end float.
I just tested the back-lash, with a DTI touching the jaw of the chuck (max radius) and indexing via mach, backlash of 0.035ยบ or if I try and wrench the table round by hand, there is about 0.04mm of play, but it's more the spongyness of the drive train than "real" backlash.
So that looks good sitting on the bench, wonder what it works out in the real work when cutting some metal !!! time to find out :-)
Greg, I like the look of DeskProto, when I have a moment I'll install the 30 day trial.
ATB
Derek
Looks good 
What kind of backlash do these Vertex tables have?
Hood