Haven't been keeping up my build log, but I've definitely gotten more done. Let me start catching up.
Time for guide rails to be mounted. Here's where I start to, let us say, depart from the normal.
I mentioned before that I ordered some typical Chinese SBR fully supported round rails, SBR 20 for the X axis, and SBR 16 for the Y and Z axes. I intended to mount them directly to my 40-8016 extrusions that make up my primary X axis and gantry, as my best straightedge shows these extrusions to be fairly straight (Veritas stainless 36" straightedge - not toolroom grade but sufficient for woodworking, claimed to be within .0015 over full length). Along the surfaces I intended to mount the rails on, I could not fit a .002 feeler gauge anywhere.
Of course the 30 mm spacing of the rail mounting hole pattern does not match the 40 mm spacing of my T slots, so I made some alterations to the aluminum mounting flange of the rails. First I removed the ground steel cylindrical rod from the aluminum base so i would not risk scratching it. I marked one end of each piece and kept each set together, so they could be reassembled. Using a 4 1/2" grinder, I made slots in the aluninum bases wide enough so I could mount them to the rails with 5/16 pan head bolts to sliding nuts in the T slots. I cleaned off the metal shavings and reassembled the guide rods to the aluminum bases. On the X rails I made them near the existing holes in case I wanted to use the holes in the future, but it worked so well on the Y axis I just slotted through the existing holes.
On the first X rail, I used my 12" sliding square to space the rail at a constant distance from one edge of one extrusion (centering the rail on the top). I assembled the SBR bearing assemblies to 3/8 pieces of aluminum plate to build my 2 X axis carriages. Across thes I clamped on the gantry rail extrusion to make a temporary gantry and used that to align the second X rail parallel to the first. My temporary gantry travelled very smoothly with light fingertip pressure. I'll count that as a success!
In a similar manner, I mounted the SBR 16 rails to the top and bottom of my gantry extrusion, except here I used the sliding square to mount both rails the same distance back from the "front" face of the gantry, again centering the guide rail on the extrusion.