New and in need of wisdom

[Jonathan]

Moved the rails on the Y axis to the top and bottom of the gantry (thanks Mocha) and I assume that was what you also meant Jazz.

Jazz will have meant putting the Z-axis rails on the plate that moves up and down, not the bearing blocks. Like mine (old picture):



However you do it, as Robin said, with the short distance between the chuck and the bed there is no need to have so much travel. You're much better off spacing the bearing blocks out further on the linear rails (this sacrificing the travel) since this reduces the magnitude of the force on each, leading to higher stiffness.

Maybe a silly question, but is the tool chatter etc linked to harmonic resonance in the frame essentially and if so would assymetric mass damping help i.e. attaching weights to the extrusions in irregular places to stop it singing like a tuning fork?

Yes, that or avoiding symmetry in the frame can help to prevent resonance issues.

I have my eye on a set of ballscrews that are 1050mm, 550mm and 350mm currently (machined), so the frames/axis are kind of sized to match.

Bear in mind Chai (linearmotionbearings2008) on eBay will cut and machine them to any length you want and the price is just based on the length so there's no need to stick to a particular set of sizes just because that's what he's happened to list on eBay for someone else.