X-Axis stopping randomly
I have a Pruse MK2/S kit that I've finally finished assembling (arrived a couple of months ago). It calibrated fine first time and I did my first test print (the Prusa logo). During that print I noticed that the printer would randomly stop when moving on the x-axis. When this happend the motor would be unable to shift it further. Typically this happens when moving from right to left though occasionally when moving from left to right.
I have posted a video here which shows this happening. You can hear the solid clunk it makes when it stops.
All the cables are well clear and do not touch, it is not catching on anything. The place it stops is never in the same place and is purely an x-axis issue.
Once it stops it will not move in that direction further unless it is reversed several cm first. I've tried googling and searching the forums but could not find any suggestions for this issue.
Any thoughts would be most welcome.
Best Answer by Vojtěch:
I'd suggest measuring the rod diameters with digital calipers or better a micrometer. The jamming rod will be thicker. I had a very similar situation on my MK3, one rod out of six was slightly thicker and while not jamming, it did make the bearings move with more resistance. (I didn't bother with RMAing, as I planned to go full Misumi anyway.) Also, have you lubricated the bearings?
Re: X-Axis stopping randomly
Was the video taken while the printer was ON; or was the printer OFF?
It could be a loose gear on the X motor, and it's easy to check the set screws.
FLAT FIRST is the rule:
1) Loosen both set screws so the gear can freely spin on the shaft.
2) Align one set screw with the flat on the motor shaft.
3) Slowly tighten the FLAT set screw until it fully contacts the shaft flat. Then torque the screw to spec.
-- at this point there should be no wiggle between the shaft and gear.
4) Slowly tighten the jam set screw until it contacts the shaft round. Then torque the screw to spec.
It can also be a bad bearing. One of the ball bearings inside the bearing shell could be broken, and when it comes up from the well to the track it can jam. Remove the back of the extruder housing to access and test each bearing. It isn't that time consuming and you don't have to disconnect anything - but you may have to remove the cable ties on the cable harness and bearings to get enough room to move the bearing out of the housing. If you find a bearing is causing the jam, best to replace all three.
Re: X-Axis stopping randomly
The printer was OFF during the video. Though when it's on it also locks up when it moves itself, I didn't want to move it manually while it was switched on in case that's bad.
My set screw was aligned with the flat of the motor shaft, but just to be sure I refastened the screws carefully and as per your instructions but still same result.
The bad bearing theory would make sense. I ran out of time to test them tonight but I'll try removing the extruder hosing tomorrow night and seeing what happens.
Re: X-Axis stopping randomly
If you find a bearing is jamming on one rod, you'll need to disassemble the X-Axis. When you get it apart try a bearing from the other rod that isn't jamming, just to be sure the rod isn't the issue. Also, let Prusa CHAT know and they should replace the defective part(s) free of charge.
RE: X-Axis stopping randomly
Ok, so removing extruder housing showed the bearings were definitely jamming on the top rod, the bottom bearing flowed smoothly.
Disassembled the X-Axis expecting it to be an issue with the bearings themslves but it looks like it's actually the rod that's the issue. All three bearings flow smoothly and silently on the bottom rod. But all three jam up and make grinding noises when on the top rod. I'll get on to Prusa chat and see if they can suggest anything or send out a new rod
RE: X-Axis stopping randomly
Ok, thats frustrating. They need to see the motor failing to move the extruder, not just my hand apparently. So now I have to take a few hours (I'm totally new to 3D printers) to reassemble it all again just to video the x-axis jamming up from the motor. Videos of the bearings moving fine on one rod but not the other (without the extruder attached) - aren't enough.
RE: X-Axis stopping randomly
I'd suggest measuring the rod diameters with digital calipers or better a micrometer. The jamming rod will be thicker. I had a very similar situation on my MK3, one rod out of six was slightly thicker and while not jamming, it did make the bearings move with more resistance. (I didn't bother with RMAing, as I planned to go full Misumi anyway.) Also, have you lubricated the bearings?
RE: X-Axis stopping randomly
So I thought I'd post an update in case anyone else has a similar problem in the future. Measuring the diameter of the x-axis rods, one was definitely larger than than other - the top one which supports 2 bearings.
So I dissembled the x-axis again and swapped the larger rod to the bottom - figuring that with only 1 bearing, there should be about half the resistance too. During this process I also lubricated the 3 bearings again thoroughly. I reassembled the printer and while the incidences were vastly reduced, they were still occuring. I also had some new frustration when during the configuration steps, after finding the 9 points and going back to do the refining step, the print head drove straight into the build plate when it got to the right-middle location. So I now have a 3mm round impact crater there. 🙁 The printer would now pass all the config steps but printing the PRUSA logo resulted in nearly a full cm of x-axis shift by the end of it from the stuttering.
Honestly at this point I was so frustrated the printer nearly went out on the side of the road with a 'free to a bad home' sign. But I walked away and left it for a few weeks.
Once I'd calmed down I looked into the Misumi rods and bearings recommended by vojtech-p6 and ordered a full set.
Once they arrived I replaced the z axis and x axis rods/bearings. Y-axis would have required too much disassembling and I still wasn't far off pitching the whole thing off a cliff. Inspecting the old x-axis rods I noticed they were both quite scratched and I also found a loose ball bearing on my desk, so both of those may also have had some impacts.
Reassembled the printer and config passed first time on everything, initial prints were great and I had my live-Z tuning sorted rapidly and without issues.
Of course, at this point for what I've spent I could have gotten a Mk3S kit and paid the Aussie GST/agent handling fees on top and been better off. But that kit may have had a different set of headaches. Anyway, the new rods and bearings solved everything and I'm now progressing through the fun of 3D printing...finally 🙂