I am a bit wary about the weight the 4 LM10UUs +2x10mm Rods will have compared to the 8mm setup but if that improves the print quality I’ll take the hit on speed hapily…
Comments are also greatly appreciated … I see that 10mm is preferred but what about the weight? LM10UUs are super heavy. Do you have some alternatives in mind? Graphite bronze bushings? IGUS?
If it is for Bowden as you say, then dual 8mm rods are plenty on a 310mm span depending on your total carriage weight.
If you have more moving mass like an extruder motor on the carriage, then 10mm may be more appropriate. Also you could look at ground linear guides (like hiwin or Chinese equivalents) vs round linear rods.
@Florian_Ford there’s a good reason many of us have moved away from linear rod. It gets expensive VERY quickly compared to things like makerslide, or openbuilds v slot.
@ThantiK well put. Even 12mm rods will just make it more stiff. I wouldn’t worry about weight there. I’m running 12mm rods with a large aluminum bed moving around and a direct drive extruder with a massive Kysan stepper. Stiffness is more important. You can always modify your jerk and accel to accommodate for a little more mass, but flex is harder to solve.
Rod mass doesn’t matter on Mendel/i3 style printers. It does matter on XY gantry printers. The rod’s mass creates diminishing returns where instead of r^4 stiffness scaling you get about r^2.5 scaling, which is worse than the L^3 scaling on deflection for longer spans. So you eventually get diminishing returns and the diameters required just get stupid.
I am designing a corexy… so 10mm would be the highest I’d go…
I will use bowden but I don’t want to limit myself if I later want (due to poor results or if I’m unsatisfied with bowden) to change to direct drive or add another hotend with direct drive.
Linear guides are quite expensive and I can’t justify the overall price for what I will use it for. Maybe for whoever has stuff to print or does it commercially that matters.
after sourcing and testing 8mm, 10mm, 12mm rods of 350mm-400mm from china, both with lmXXuu’s and with bronze graphite (self lubricating) bushings and i would definitely go with the bushings over the bearings any day. they are about the same price (sourced from china) and you get more choice in terms of width and length. for the same price they are quieter and smoother.
that’s if you decide to go with 8mm (which i wouldn’t), if you go with 10mm or 12mm it’s better to go with an mgn12c/h type of linear rail/slide - i sourced 3 mgn12’s for just under 20$ each (which is all you need for a corexy) and while the price is not far from the 15-18$ you’ll spend on rods + bushings / bearings, in performance (smoothness, quiet, stability, load bearing) they are not comparable - which is to say they are ages better.
It’s not really the motion system but more of how long you want to span with the rods. That’s why something like the tantillus which had 8mm rods and some of the absolute best print quality worked so well- it was very very stiff with a small frame. To do the same thing larger you need to brace and use larger rods
Ok, seeing the massive difference in the poll I started “porting” my 8mm XCarriage version to 10mm and man it was not as straight-fw as I would have expected it to be.
Due to the increased size and the fact that I needed the nozzle as well as the belts in the same places as before, I had to do a lot of tricks which I have somehow managed to do.
… I see that 10mm is preferred but what about the weight? LM10UUs are super heavy. Do you have some alternatives in mind? Graphite bronze bushings? IGUS?