Quote Originally Posted by Gary View Post
I doubt you will be able to run from the center, even with a stiffer machine using profiled rail can crab, and you are using MDF and this will cause you big problems.
Even running the screw through the center will still casue you problems.
Have to agree with Gary here, using open bearings will always cause you crabbing problems which is why I dismissed them for my design, but driving from both sides will soon sort that out.

Though, I have built up my X axis gantry yesterday on my machine which has a bed size of 1000mm x 600mm and using 20mm THK linear bearings gets virtually no crabbing, I will be driving this machine from the centre. It is a pretty solid all aluminium machine which does help though. will get a clock gauge on it later to measure it but it is not a lot.

Gary - Don't forget to send me those 16mm ballnuts when they come in, they are the only piece missing now before I can get up and running.