MK2: moving gantry router for metal cutting - comments sought!

[Voicecoil]

Aluminium has better vibration damping than steel. A very general rule is, the more springy something is, the more it rings.
Simple experiment is take a couples bit of steel and aluminium bar, and give them a tap. The steel will ring far more than the aluminium. Even cast iron bar will ring more than aluminium. Which reminds me, only certain grades of iron have self-damping properties.

I dug out some damping tables (I've long had an interest in this sort of stuff, being a loudspeaker designer) and we have \mu values of:

Aluminium 6061: 5 x 10-3
Mild steel: 0.9...1.4 x 10-3
Grey cast iron: 30...90 x 10-3

Oddly some copper manganese alloys have high damping factors, but sadly I don't see much that for sale, hey-ho.