Base plate rotates in place - how much is too much?
I'm seeing what looks like small per-layer horizontal shifts in my prints. I've been through the basic "How to improve your prints" at and I'm struggling with the bearings. I've tightened the Y-axis bearings as much as I dare (hard to tell if it's moving smoothly with the belt and stepper motor still attached) and I can feel the base plate rotate in place, just a little, when I push on it. (By comparison my MK2s doesn't rotate nearly as much.) The smooth rods the Y axis runs on don't move noticeably, and I can't feel the bearings moving in the U-bolts. But I can even hear the single bearing running forward and back as I twist the base plate. I have a little spray-on silicone lubricant I've applied to the rods a couple of times to no apparent effect, but I don't own any thicker grease (I don't think either kit came with any?). Movement has always been fairly noisy. The printer was running better than it currently is before a hot end replacement and the MK3->MK3s upgrade.
Is this an unacceptable level of looseness? It certainly seems like it could account for horizontal shifts large enough to roughen vertical surfaces. If so, is it a matter of adjustment or replacing bearings? Bearings and rods?
RE: Base plate rotates in place - how much is too much?
Most hardware stores have white lithium grease that should be used with the bearings. Also, synthetic grease like SuperLube is acceptable. About $5 a tube.
But some rotation in the bed is due to normal bearing play (bearings and rods are spec'd somewhere around -0.005 to -0.010 typical clearances, but also bearing wear adds to the issue. It gets worse over time, and gets especially bad if the printer has run without grease for an extended period or time.
Bearings on the Y-Axis should be snug, and not wiggle in the U-bolts. But too tight and the U-bolt crushes the bearing.
But most shifts like those in your images aren't due to this play; generally it's other factors. Loose belts and drive gears are often the culprit. Try snugging up the belts and see what that gains.
When the bearing wear gets larger, after hundreds of hours of use, I do this:
RE: Base plate rotates in place - how much is too much?
Check and see if you have the branded or none branded bearings.
The none branded bearings are not quite as good and can move slightly. Or if the bearings have worn you will get movement.
I now use this to hold my Y bearings, https://www.thingiverse.com/thing:2823171
Had no probems, i.e. no U bolt to come loose or be too tight
RE: Base plate rotates in place - how much is too much?
ps: That photo is my printer with too many hours on OEM rods and Misumi bearings that were packed with grease at installation... bearings still wear, even with grease. This set lasted two or three times longer than the Prusa supplied non-lubricated bearings. I tried the 6-row LMK ... and can't really recommend them, they lasted no longer than the four row LMU style, perhaps less.
I do have a new set of rods and bearings somewhere between the Misumi factory and my mailbox, and they'll be cleaned and packed with greased before installation, too. Once they are on, I'll remove the custom rotational dampener.