April 17, 2021

Filling Aluminium Tube Gantry

2 min read
I’m starting to design a new router. I want it to be pretty heavy duty...

I’m starting to design a new router. I want it to be pretty heavy duty so I started doing some simulation in Fusion 360 on the moving gantry beams to start.

Comparing chunky aluminium profile extrusion, steel rectangle tube and aluminium tube with a granite core.. so far the stiffest result for the least weight is the aluminium rectangle tube with granite core. So I’m quite pleased with that.

Gantry-Sim-Ali-Extrusion.jpg
Gantry-Sim-Steel.jpg
Gantry-Sim-Ali-Granite.jpg

I’m now looking in to the practical aspect of filling the tube and the best mixture etc.

Can someone please help me understand the differences between epoxy granite and polymer cement such as Polycrete – Polycrete is a Granite Strength Resin Repair Mortar for Concrete or Asphalt – Internal or External | Vuba

Are they the same thing? Polycrete has a resin and a hardener and then a ‘powder’ and I’m not sure what that powder is; granite powder?

If I went with Polycrete I presume I still need to add an aggregate such as AlOx or quartz pebbles?

If I’m best going with epoxy is something like Xencast X6 suitable? Xencast P6 Toughened Polyurethane Resin – Easy Composites

I’m also wondering about attaching rails. Do you think the 6.35mm wall of the tube is enough alone, possibly with over-length bolts that I can cast the fill around (and remove them?!), or do I need to add some kind of internal inserts? In the same vain of thought do I need to add something like bolts through the tube walls to aid adhesion of the fill, or is it going to stick well enough to the inside the the tube if I simply wash it down with some acid first to remove oxide?

Advice appreciated.

Also, I intend to cast the fill around a threaded rod that passes through the center of each beam and be tensioned during the cure. Then it will keep the fill under compression as well as give additional fixing for the gantry sides.

I do have a vacuum pump so I would de-gas the mixture before pouring and possibly also possibly pull a vacuum on the tube once I cap the ends.

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