Quote Originally Posted by fvfdrums View Post
Rough dimensions: 120 x 800 table size
Typo surely, 1200mm? Rest of my post is based on the assumption that it is 1200*800. What Z-travel?

Since you want to machine 'aluminium at a reasonable DOC' then an adjustable height bed, or very small Z-travel is critical. Clearly a small Z-travel is quite limiting for machining non-metals, so the adjustable height bed is preferable.

You should be able to get the profile rails on eBay for a good price - certainly a lot less than new. 15mm rails will be good compared to any size supported round rail since it is the pre-load that makes the profile rails more rigid. If you find bigger (20-25mm) rails then that's good, but it's not worth spending a lot more on them. Since you seem to have waited 5 years to post I guess waiting a bit longer for the right price isn't a problem!

You could try 4 rails on X as you suggested, I considered it for my machine. The problem with the supported round rails is that the bearing blocks are not preloaded, so even though load ratings are plenty high enough adding more bearings doesn't magically pre-load them so it will still be worse.