Quote Originally Posted by FlyHighRC View Post
.. How far should i keep the bearing carriages apart? ..
With a single ballscrew in the centre then racking becomes a problem whereby the gantry can rotate or twist if you are cutting anything towards the edge of the gantry. To minimise this you can space out the bearings further, but there is a compromise on travel.

With twin ballscrews all these problems go away, which is why it is highly recommended. The gantry cannot rack as a ballscrew holds it at each end. Your considerations then come down to placing the bearings so that the centre of gravity of the gantry (which will be somewhere behind the spindle centre line) and the cutting tool centre line both lie within the region between each bearing, as viewed from the side. If you need to deviate from these positions then don't worry as the profile linear bearings will take quite a load.

As I guide I would say between 100-200mm is about right, probably going closer the 200mm end of the range, giving you maximum travel.