Wobblycogs CNC Mk2

[Wobblycogs]

Well I've broken rule number one and bought the first pieces of the machine before the design is properly finished. I decided to take the plunge and get some second hand THK profiled rails. They are a bit longer than the supported rails shown in the design above so I'm beefing up the gantry. The X and Y rails are SHS15R@1040mm and the Z is SSR15XW@410mm. I've since read that SSR are better suited to horizontal alignment because of the bearing arrangement but to be honest they are working so far below their rated maximum load I'm not worried.

I have a quick question about mountings the rails on extrusion though.

For the Y-axis I was thinking of doing this:



Does this look like a good idea? There's 4mm of aluminium and the bolt is an M5 so that would mean 5 threads. I'm concerned that if there's the slightest bit of warp in the extrusion it'll throw the rail out because it's fairly snug in that central channel.

For the X-axis I've got a couple of options:



Neither seems to be a great option but the one with the rail over the T-slot looks precarious to me.

I'm seriously considering ditching extrusion and going with rectangular section. Any one know where I can get some with decent wall thickness?

EDIT: Scratch that last question, I must be going blind, Aluminium Warehouse do 2500mm 100x50x6 box section for £52. That makes it significantly cheaper than the 60x90 extrusion I was going to use.