I previously posted some information on some stainless steel tube that I thought would be suitable for use in the IE of the MPCNC. It was not a true metric tube but rather 1″ (25.4mm). While it worked perfectly with my printed corner blocks and roller F, it is not perfectly suited to the middle assembly.
The problem I have found is the extra 0.4mm causes the tube fitted to the z axis to foul on the bearings that support the tubes for the gantry and vice versa (does that make sense?) This being the case, I went back to the drawing board and began searching anew for suitable tube.
I had previously found 25mm alloy tube, but I was not sold on the surface of the tube being hard enough for long term use. I envisioned the bearings cutting grooves into the malleable alloy. But I think I have found a solution in the form of a hard anodised/hot dipped alloy tube available through Ullrich Aluminium http://www.ullrich.com.au/
It is very cheap (cheaper than the stainless tube I previously listed) nice and rigid (at 3mm wall thickness it rivals the stainless tube over similar lengths) and the surface finish is very hard. The finish is a hot dip chrome like plating with a anodised coating to prevent corrosion (used primarily in bathrooms). It is impressive how hard it actually is. For example. The 316 stainless tube was showing marks/wear from the bearings straight away, the hard anodised alloy on the other hand is totally impervious to wear from the bearings (so far).
Very impressed with this tube, and very well priced.
I will post a copy of the invoice for anyone who in interested in purchasing some for their own build.