My new 6040 improvement plan.

[Zeeflyboy]

Yeah but in your example of the Z-axis bolted to the gantry, it can't pull away... a wheel isn't attached to the gantry it just rides on it. Sure it can't push into the gantry (well, beyond what degree flex of the wheel allows) but it can pull away from it. That's not even getting into the problem with swarf getting trapped under the wheels and wearing down the relatively soft aluminium surface.

What you need is something that can't push towards the gantry or pull away from it - ie a supported rail. Round supported rail however has the drawback that the shitty bearing becomes the weak point (even shittier than a fully round rail bearing is)... enter profile rail. Now you come full circle to what I was saying in the first place which is that the unsupported round rail is just inherently inferior to profile rail for milling anything substantial.

Honestly, what you are suggesting is a waste of time - imo the improvements will be minimal if noticeable at all. Combine that rear plate with proper linear rails and now you have a substantial improvement but are at the mercy of the next weak link. And onwards the chase continues.

Listen to me or don't, but I would sincerely suggest you just get cracking with your machine without any major effort/changes and take it from there. I would say after a few mods and chasing your tail you will come to the conclusion that it's better to just chalk it up to a good entry machine for learning/playing around and decide to build your own one rather than constantly trying to work around the inherent weaknesses of the design. Either that or you will decide that for whatever your intended purpose is, it's just fine.

Note that when I say the inherent weaknesses of the design, I'm not just talking about the unsupported rails... there are MANY issues with these machines and to address them all you would effectively end up building a new machine anyway - which is what I am now doing myself.

Just trying to save you some time and money in the process. Up to you if you want to heed that or not.