Quote Originally Posted by JAZZCNC View Post
Ah so you've seen me mention sand before.!! Yes dry kiln sand works good and is easily removed.
That or seen someone else mention it - it's a well documented solution.

I'd go for epoxy granite over concrete. Concrete moves/warps after it's set and since you're using profile rails any movement in the piece they're mounted to could cause serious problems. If the rail is bent ever so slightly the slide coefficient of friction increases dramatically, so if this happens over a long period of time you probably wont notice until the machine stalls due to the greater power needed to move each slide. By that point some serious wear could have occurred to various parts in the system.

Frame looks appropriately sturdy, but I'd be inclined to add some smaller box section to link the legs. It wont cost much compared to the rest of the frame and could help with resonance, since at the moment you have a large mass supported by legs (rather like a cow which wobbles a lot if you push it!)