Comments sought on new build: A CNC Router for RC Gliders and Planes

[njhussey]

I really should stop playing about with the design and get on and build the damn thing.....but I keep reading posts on here and changing things. Was going to go with a framed gantry but then everyone says to keep the sides down to a small height to increase the stiffness.

Here's my latest design, can you guys comment on it please? It's going to be predominantly for cutting balsa and ply, the odd bit of plastic, carbon fibre and possibly aluminium components for RC planes, helicopters etc. There's only 100mm of height, but as the thickest balsa I'll be cutting is probably 1/2" it should be fine.

The box frame is 40x40x3 mild steel, the flat plate is 12mm 5083 Ali, the rails are SBR 16, most probably from linearmotionbearings2008. There are a few things which need tweaking to make them fit (Z axis bearing plate needs to be made the same width as the bearings etc.) so I'm aware of them, it's just the basic concept/design.

[Jonathan]

I would make the mounts for the X and Y stepper motors/ballscrew fixed end bearings stronger since they have to support the axial force on the ballscrews, so any deflection in those mounts directly causes inaccuracy in the tool position.
On my machine I have SBR20 and SBR25 rails and it is clear that the 25mm rail system is substantially stronger, presumably (apart from the obvious reasons) because the bearing blocks have an extra row of balls. I urge you to consider at least using 20mm rails as it shouldn't cost that much more, although it does mean increasing the box section size to 50mm.
Have you considered using pulleys and timing belts to drive each axis? This can simplify mounting the motors, reduce resonance, improve feedrates or resolution, among other things.