DIY Build of Aluminium CNC Wood Router without Workshop & Tools

[Jonathan]

The BF side bearing is only there to stop the screw whipping which does not require particularly great rigidity in the mount. This bearing should only be subject to radial forces, so as long as the mount is strong enough in the Y-Z plane it will be fine. I would make it a bit stronger than you have currently drawn, but wouldn't go so far as replicating the other end mount exactly - you can save a bit of material.

If you're buying the Hiwin rails new then there's no need to get 20mm for this size machine - 15mm is perfectly good for the vast majority of CNC routers. This could help with making the Z-axis more compact. If however you find the rails cheap on eBay then by all means use the larger sizes. You shouldn't have much difficulty finding a good deal there at least for the shorter rails.

As irving's said, recessing the motor mounts is an easy strong way to get round the short shaft problem, here's a few examples: