Comment on Linear rail mod on Anycubic Kobra 2
rambos@lemm.ee 7 months ago
Industrial linear rails can cost more than the printer itself. They should be mounted on proper flat surface like tooling plate (aluminium extrusions are far from best option) with extra attention to mounting tolerances. Smooth rods and “wheels” are way more forgiving to any missalignement.
Well…there are knockoffs like hiwin on ebay, and they seem to work for many people even mounted on aluminium extrusions. I think you should get your frame as square as possible first and see can you stay on wheels motion system to avoid upgrading cost. If frame is not good enough for wheels I would be afraid of even more issues with rails (binding and simmilar). But keep in mind I have no experience with your printer or any kind of wheel system and I never did upgrade from wheels to rails or anything like that. Im just trying to help, but hopefully someone who did that kind of upgrade can provide better answers
DreadPotato@sopuli.xyz 7 months ago
Hmm, fair point. I was not aware that the “cheap” linear rails would be just as bad as the design currently used. That’s a bit disheartening since the current design leaves a lot to be desired and honestly isn’t very good/well implemented.
I was under the impression that the linear rails (I’ve been looking for ones in the $40/pcs range for 320mm length) were a better solution.
My frame is as straight as I can get it, but that doesn’t really affect the movement on X or Y axes independently, only how well the print head (X)moves in relation to the bed (Y). I have issues on the axes independently, which is not really affected by the squareness of the frame.
rambos@lemm.ee 7 months ago
I thought your frame acts also like a rail for wheels.
I think they should be better, but smooth rods and wheels work quite good as well. Linear rails are better than smooth rods and smooth rods are better than wheels, but only if built correctly.
There is obviously some missalignement in your setup and the reason why you cant fix that might persist after upgrade. What concerns me the most is mounting Y linear rails not parallel enough (they might not move at all due to binding, while smooth rods or wheels could still work)
DreadPotato@sopuli.xyz 7 months ago
There is a single extrusion, in the middle, running parallel to the Y axis below the bed, with rods on both sides that the bearings travel on. So it’s not affected by the squareness of the frame.
Likewise for the X axis, there is a single extrusion mounted between the two vertical extrusions, with rods on that the print head travels on, again this is not affected by squareness either.
Squareness of course comes in to play when the print head is positioned relative to the bed, but I actually have decent (and consistent) print quality.
rambos@lemm.ee 7 months ago
Using single rail for each axis would exclude most of the issues I was concerned about. When I mentioned frame squareness, I was thinking about all geometric tolerances including rails being prallel/perpendicular to the frame.
Honestly my knowledge about linear rails becomes kinda useless after seing how people use them on their printers. Example: mounting them on alu extrusions or using them as a frame should be wrong, but looks like many people have good results.
Again, someone who solved that issue on the same or simmilar machine might be much more of a help than anything I wrote