Mini Unable To Print Round Circles Now

My Mini was used as a loner to introduce people to 3D printing. One of the loaners decided to put red lithium grease on the smooth rods to help reduce the noise (do NOT do this). Shortly there after the IGES bearings wore pretty quickly and I replaced them all but the z-axis bearings. After that I took a break from printing for six months or so and am no longer able to print perfect circles. I’ve googled around a bit and haven’t seen any good leads other than checking the belt tension and making sure x and y are close to the same tension, but that didn’t help. Any ideas?

Just looking at the picture it looks like both X and Y belts are massivly under tensioned. But if you know to check that already, its probably not that. Maybe a loose X or Y belt pulley? The tension would be right then, but it would still be slipping on the motor shaft.

if its not that, I’d be inclined to start with a re-firmware and a settings purge and go from there.

The sudden direction changes point to slipping on the X/Y axis. Kind of the screws on the flat it looks like.

Master P, thanks for the info. I’ll re-run the belts and ensure the gear ends are tight. Any tips of the zen of belt tensioning.

Kmanley, I think you mean the same thing?

They should make a strumming noise like a string bass string when plucked. I don’t admit there is such a thing as a belt that is too tight. I suppose if it causes the printer to implode and turn into a ball of neutron I’m that might be too much. The loose sets crew pulpy issue will also drive you crazy the first time you run into it and aren’t expecting it.

The direction of the layers on the X axis parts I would not say that. I have replaced a number of broken X parts and have seen that you can get the belt too tight. :frowning:

So I took off the belts, and the gear on the stepper motor and ensured they were set correctly with the set screw and secondary screw, reinstalled both the gears and the belts. No dice. I flashed the firmware back to the v1 Mini firmware (I believe I got one of the 1st thousand). No dice. I re-flashed the firmware with the latest (Marlin_Foxglove_Albatross_or_Brambling_1.0.2.2.hex) No dice. I’ve double checked the connectors to the motherboard and inline to ensure good connections. All the wire is shielded for EMI purposes. What’s left?

With the belt off the x and y axis, do they move freely? The only thing I can think of that isn’t electrical would be extreme binding or carriage sticking. That or maybe a broken motor shaft? Are the idler bearings turning correctly? I’m trying to figure out what a loaner printer might have encountered that would even do that that isn’t belt related.

They do not move freely. There is a fair amount of resistance at all times on both axis. I ordered the 8MM bearings directly from Lulzbot. I also followed the ohai page to explain re-assembly.

Well, there’s your issue. You either got shipped the wrong bearings, the allignment of the bearing holders is off, or the bearings are installed in the holders wrong (bearing sitting on the notch, etc.) It may very well just be allignment. If one of those bearing blocks is tilted 1 degree, it can really induce alot of drag. I would loosen all the bearing mounts slightly and then move the carriage back and forth a bunch without the belt on still, and see if it loosens up. If not, pull the rods and the bearings and holders and try them all individually until you find the problem unit or determine you need different bearings.

Just to confirm, not lubrication on these bearings, right? One forum mentioned light PFTE grease

Do NOT use lubricant with igus teflon bearings. It won’t help, but it will make dirt and crud stick to your bearings and your rods. If you applied some PTFE grease and wiped it off really really well, it probably wouldn’t hurt anything, but it would not help.