My new 6040 improvement plan.

[Zeeflyboy]

Okay, I'll look at profile rails.
In your opinion, what are the Chinese profile rails like? Their prices look fine, but most of the branded ones I've seen are just far far too much for me.

Seems people have got on fine with Noulei from what I've seen... it'll still be an order of magnitude better than round rail either way. Some good sellers on Aliexpress (I've bought HIWIN there before and been very happy) that will supply to your specs.

Have at least a rough plan though before ordering anything, and do bare in mind that you are addressing one of many mechanical weaknesses in the design... so if the plan is to continue to mod this particular machine, worth having a plan of what comes next and whether that will affect your mods here. For example, to change to profile rail you will likely have to make a new Z-plate and spindle mount. Is it worth changing that over to profile rail as well to avoid having to change it twice? Now your supported rails on the Y-axis are a weak point, then the ridiculous floppy bed, then the thin bendy gantry arms, then the piss poor use of retaining bearings for the ballscrews etc etc.

You see what I mean I hope... Just think it all out (almost like a new machine design) before committing to buying anything.

Then once you've done that and other mods, now you have semi respectable rigidity and realise your extrusions aren't straight enough... at best out come the shims, at worst another redesign. Then you decide you could have done a better job just designing from scratch. It doesn't end :)