Hi Procato,

Interesting design. I drew something a bit like that a while back but didn't like the loss of X travel and obstructed access to the spindle for bit change. But I was working with upgrading an existing machine so if these factors are already considering in the geometry of your clean sheet design then it should be OK.

I should point out that the Z axis box 'front plate', i.e. one closest to the ballscrew needs to be lapped the other way to the side plate. You are trapping precision height linear rails against each other and they will want to be a certain distance from each other. Unless you can machine the Z axis side plates to very fine tolerance, then lapping them the other way is better as you can use slightly oversized bolt holes coming in from the sides and lightly clamp the assembly before nipping them up.

I can't see in any of the sketches but assume you have a third linear profile rail at the front for support? Should work very well for stiffness, but you also need to be careful on the order of assembly of the Z and Y. The front box section probably needs to be attached last once everything behind it is set. If this is your first build you need to think about the imperfections of machining and building and make sure things can be built in the right order with pre-loads or free running checks made as you progress. Try to build it in your mind.

As for Z axis racking I wouldn't be too concerned about it based on the design and what you want to do with it.

Looks like you've got twin Y axis drive with a twin pulley on the ballscrew nearest the stepper motor. So it looks like you want to link a short belt to the first ballscrew, and then have another belt between each ballscrew. That's no problem but make sure you can tension them. The stepper pulley belt is easy - just add slots which it looks like you have done. But the belt between the ballscrews will need an idler pulley and it looks like it's a tight fit between the side plates. Have you provisioned for one? If so make sure it can take up the required slack as belts come in fixed sizes (although I believe you can have custom ones made).