Printing linear rails

Has anyone managed to successfully print high quality linear rails?

I know this is on the list of “things not to print”, but we have to try, right?

Printing vertically the layer lines cause friction, printing flat they come out very slightly bent, not enough to notice by sight, but enough to cause issues with machinery - a tightness or wobble near the ends of the tracks. (And a straight edge will reveal a banana dip in the center of a fraction of a millimeter).

Have tried all the standard things: even out temperature by raising bed temp and lowering nozzle temp, turn off fans, close printer door, then print slowly and monotonically with thin layers, then put a raft on in case the heat bed is bent.

Maybe your heatbed is the source of the problem. Try putting a straight edge across it and look for daylight in between. I’ve heard this is a well known problem affecting quite a large number of bambu heatbeds. If you don’t start out flat, it’s no surprise you won’t end up flat either. A possible workaround is attaching a very rigid buildplate (glass, garolite, or similar) that’s also thick enough it won’t bend or bow in any meaningful way.

Hmm… if i put an 8-10mm glass/aluminium etc sheet over the heat bed, is that going to mess up the self-levelling?

It shouldn’t need to be that thick. For instance, 2mm of garolite is plenty flat and rigid–well, at least it has been for me.

Regardless, in answer to your question: I don’t foresee that self-leveling an 8-10mm thick build plate would be either a problem or a gotcha. Just to be fully transparent though, the thickest I ever tried was 2mm thick garolite

If I had programmed it, and it said it was level but a whole centimeter from where I expected it to be, my code might just choose to raise an error. It’s more likely to be a sensor error than the user adding a centimeter thick build plate.

I’m thinking tha a sufficiently thick raft might compensate for build plate issues, but perhaps it does not. I have some 8mm alu somewhere, if that does not work I shall purchase something thinner and rigid as you suggest. No point having it be flexible on the bed.

edited for spelling

Your bed isn’t flat enough for that and even if you try the above mods, neither are the carbon rails - which are specced at ±0.1mm bow/deviation over the length