Aluminium FEA optimalized CNC router

[PotatoMill]

It's an interesting design and if you really want to do the Z axis that way then I would add a reinforcement panel on the front outer face of that RHS box to spread the load of the spindle out to the edges (I assume the spindle is mounted just on the front face and not sandwiched between the front and rear faces?). Say a 8-10mm thick aluminium plate as wide as the RHS and enough height to pick up on the 4 spindle mounting bolts. Otherwise the loads will go into the weaker membrane panel and not be transferred to the stiff edges. If you simplified your loading condition on the analysis this will not show up.

Same could be applied to the rails, I would add a thin strip of say 6-8mm thick steel, by 30mm wide on the inside of the RHS directly where the rails mount and screw the rail bolts right through into it.

Also in post#9, first picture, the upright bracket holding the ballnut to the Z axis is too thin. It needs to be approaching the length of the ballnut and then bolted down in 4 places. It should be a 'boss' not a 'bracket'. Also the plate it sits on is on the small side if you are trying to maximise performance. This needs a better connection to the upright Y axis plate. As drawn it will twist when loaded. Maybe a similar plate parallel to the current plate but above the ballnut would work trapping the ballnut in-between 2 plates.

Keep exploring, it's good to see something different every now and again.

The spindle mount is bolted from the front and the rear of the large square steel tube. However I'm not satisfied with it because the mounting of the plate can maybe drag the clamping around the spindle apart. I also need to make tramming possible.

The nice thing with the steel square tube is all the space for mounting parts. If I eventually want to add a 3:1 belt reduction on the spindle, for steel. (whisfull thinking)

Plates on the inside for the rails sounds like a good idea.

The upper ballnut connection is made of 3 layers of 10mm aluminium plates, where the lower one is bolted to the large steel tube. The grabCAD model should show it better. Or I'm misunderstanding something.

Thanks for the comments it have helped me removing a lot of weak points.

Edit: I see I forgot to add the mounting holes for the backside of the spindle attachment on the square tube.