Re: Filling Aluminium Tube Gantry
Polymer concrete often refers to polyester resin. Polyester resin shrinks considerably during curing and generally is not a good choice.
The threaded rod down the middle is not needed for epoxy granite.
You would be better:
Thicker wall tube (less local vibrations and you need something to fix into)
Epoxy granite lining the inside of the tube
Hollow middle - you can use a piece of PVC / similar hollow tubing - material close to the neutral axis does not contribute to stiffness much.
Ends capped.
Epoxy does not stick to aluminium well. I'm not sure how you will do with this. Generally the best adhesion is done by sanding the alu with a course grit with epoxy on the surface. This roughs up the surface (mechanical bond) and removes the oxidised surface allowing the epoxy to bond (epoxy has to be on there to prevent oxygen contact and oxidation). You can then add more epoxy / stuff which will bond to the epoxy.
7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)