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Y axis has a "drag" when off then will "lock up" when hot

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Okay had my Ender 3 (not Pro model) since 2018 and have fixed a few things here and there, upgraded a few other things, it started acting up so had to do a little "tune-up" a while back after which it went right back to working just fine for quite a while and now "Twitchy" is once again living up to its name. And doing the oddest thing - the Y axis has a "drag" in one spot when I move the bed manually when it's off and then when it gets far enough into a print, the Y axis will "lock up" and the bed will refuse to move on the Y axis. The X and Z axis will work with no problem but the Y axis is pretty much locked down and not working. So I shut Twitchy off and let it cool off, cussing it all the while and once it's completely cooled off, I can finally move the bed on the Y axis - with a slight drag in one spot.

Now Twitchy is in a nice glass/wood enclosure me and my other half built so unless I really listen hard, it's not easy to hear the printer running but it's never really been that loud anyway so I don't know if it made any noises on the first print that it started doing this on. And the only thing I've done to it before it started doing this is move the cable connecting the hotend to the motherboard under the bed a little farther away from the bed. I've seen some people add a printed "chain" to move that cable away from the bed but I just added a Command hook to the back of my case and it holds the cable slightly up and away from the bed.

So the first time I saw this happen was on an 8 hour print and it printed the first 5mm fine then the Y axis locked up and Twitchy hasn't behaved since. I've attempted three other prints that I have successfully printed before this and each one has the Y axis lock up after a while (random timing too) and it won't unlock until the printer is completely cooled off. I've gone over the belt to visually check it for any messed up teeth (and the drag spot has now changed places after this) but I only flipped it over while on still on the axis and I haven't taken it off but I didn't see anything wrong with it. I've also cleaned inside the case and on the printer everywhere my vacuum hose could reach on the axis and around it so I'm 99% sure there isn't any debris on the axis or the belt. I've also visually checked the teeth on the motor end and those also look fine. The nuts on the wheels under the bed are tight like they should be and I also can't see anything wrong with the wheels themselves.

Now I don't mind replacing the motor or the belt or the wheels but I need to know which one to replace (and which kind I should buy) before I go fiddling around with the one of the few things (the Y motor) that came pre-installed on my Ender as I got the one I assembled myself.

So does anyone have any idea what is wrong?

fact that it happens when it heats up and stops when cool and the fact that a stepper motor is actually several coils/micro stepping is in use/few other minute bits of drag and I've seen this before, I'm gonna say that it's 98% a single bad coil and thermal expansion is at play. That is of course that you made extra sure your z stepper cable is actually intact and not pinched somewhere. Keep in mind that the clips inside the cable end may be too weak to keep contact. To check for sure sure sure without having another printer or stepper on hand is swap it with the Z screw or extruder steppers to make it heat up faster. Swap it with the X stepper if you don't want to mess with the end bit but it won't heat up as fast. The X axis isn't "flinging" as much weight (or ever growing weight) like the Y axis is. I have my extruder and Z axis motors covered with spare raspberry pi heat sinks so I know they heat up very fast. If you swap it with Z axis use a layer height that's a multiple of 0.03 so it's disharmonious to the magic number and more prone to get stuck in a spot. (0.18 or 0.21) If it is powered off and still locked up and you have removed the belt and cannot hand turn the stepper, make this clear, used till it locks up then unplugged and still cannot be hand turned then it's a truly F'd up stepper and needs replacing. If you MUST use it then the X axis remains the coolest. This is exactly why I have some steppers covered in heatsinks and NEVER EVER EVER over tighten your belts! Ender 3 belt tensioners are plentiful on thingiverse so you can feel in real time the loading effect it has.

If you need a new one just go get any ender 3 compatible one. End pin connector is gonna be 6 pins with pins 2 and 5 unused so just make sure you get a regular sized one and don't over-tighten your belts and/or heatsinks. Surprisingly every single stepper in the ender 3 is the exact same stepper, yes, all of them. Heatsinks, I went to eBay and got a 50 pack of rasPi self sticking ones and just plastered as many as I could on ^_^

The motor could be overheating. Try swapping it with one of the others and see what happens

I should probably get a new one if it's overheating, any chance you know what the specs on it are or how to find out the exact one I need?

I've seen the ones on Amazon but they don't show the "teeth" part in the red box on the picture as being part of the motor. The official replacement video shows that part as part of the motor (or at least already on it) so I don't even know if it's supposed to come off the motor or if it's supposed to be part of the motor. For $16, I don't mind just buying the replacement but I don't understand why the replacement motor doesn't look like what's on my Twitchy and why the video doesn't show it being attached to the motor before the motor is installed.

Before going the new motor route I'd fully disassemble the bed and check the rollers and rails (also for squareness to the frame) for wear and/or obstructions. First I'd check the bed with the belt removed. if it still sticks then take it off as the belt is not the issue. Remember when problem solving tackle one thing/part at a time so you will know what was causing the issue when you find it. Pull everything off at once then you may solve the issue when you reassemble but you won't know what the cause was if it comes back

Do I absolutely need to disassemble the bed to get the belt off? The very few videos I've found that go over replacing the belt show taking the bed off completely and I'd rather not do that if I can rule out the belt otherwise. Is there a way to at least loosen it without taking the bed off or would loosening it the same way I tightened the belt tension without installing a tensioner do that?

Is there a special way to check the squareness or do I just go grab a carpenter's square?

Also what does the belt look like when it's "worn"? I have carefully flipped it over and checked the teeth as much as I can while it's on and didn't see any obviously broken/worn off teeth but there are spots I couldn't fully see.

What do the rollers look like when they're worn? I didn't see any obviously flat spots when I moved just them by hand but now there seems to be two more snags for a total of three spots that drag when I manually move the bed.

The bottom half was already assembled when I got it and I have replaced the springs and added M4 nuts but aside from that I never really messed with the bed aside from the one time that the rail moved (long time ago) and I re-leveled it with my three way bubble level.

Thanks for guiding me on what steps need to be taken. I do enjoy using my Twitchy and would rather fix it than buy a new one even when the stupid thing lives up to its name.

Do I absolutely need to disassemble the bed to get the belt off?

No just turn the printer on it's side and you will see where they attach to the bed.

Is there a special way to check the squareness or do I just go grab a carpenter's square?

Just use an accurate square

Also what does the belt look like when it's "worn"? I have carefully flipped it over and checked the teeth as much as I can while it's on and didn't see any obviously broken/worn off teeth but there are spots I couldn't fully see.

Visual inspection for broken teeth plus pull on the belt, it should give a little but not noticeably stretch

What do the rollers look like when they're worn? I didn't see any obviously flat spots when I moved just them by hand but now there seems to be two more snags for a total of three spots that drag when I manually move the bed.

They will have well worn grooves in the wheels, but more important are the bearings, if they have dried out then they will stick. Also check the channels in the extrusion to make sure no debris has got stuck in there

The bottom half was already assembled when I got it and I have replaced the springs and added M4 nuts but aside from that I never really messed with the bed aside from the one time that the rail moved (long time ago) and I re-leveled it with my three way bubble level.

Thanks for guiding me on what steps need to be taken. I do enjoy using my Twitchy and would rather fix it than buy a new one even when the stupid thing lives up to its name.

You may find some of these videos useful

https://www.youtube.com/playlist?list=PLVctiritf4zQhJeXFqaimrCKjhH9DPza1

Good luck

Okay over the weekend I broke down and disassembled the bed on Saturday - I always have to wait til the weekend to do major work on Twitchy as I work from home and try to keep the weekdays for work time, I've got a guy I can send print files to so I do that when I can't print.

So I started taking the bed apart piece by piece to figure out what was wrong and I even made sure to have my other half there as a second set of eyes and see if there was anything I could be missing.

First thing I did was take off the bed (after removing the glass bed) and double checked the rollers underneath (after I detached the belt from it). I took off the two on the right side and checked them. Those were just fine, well greased and everything (as the oily marks on my hands showed me) then I checked the left rollers still attached to the bed and they also were fine. Then I had my other half check behind me on both sets - after looking closely, he said they were fine too.

Next was the belt itself. I manually moved the belt back and forth over the teeth on the Y motor, being sure to keep the tension as much as possible and my other half noticed it would "jump" when it hit the snags. And he carefully looked over the belt teeth under the nice bright flash light and he noticed the worn spots that I didn't see, which I really should go glasses as I saw the same worn down spots only under the magnifier. Course he's got glasses so he spotted them easily. So I jumped online and ordered an X and Y belt set (I'll have the X belt as a spare just in case that one acts up next). It came in Sunday afternoon and I installed it then reassembled everything.

Then was test time. I started up a print I've done before and let it run. And it did okay until the filament stopped coming out halfway through. So started print #2 and it spit out the first bit of the base then no more filament. Then did print #3 and again, got the base down and stopped. So I figured I'd change the nozzle as this is what it does when there's a clog and I've got way too many spares to worry about one that's acting up so I just go ahead and change to a fresh one.

So I changed the nozzle earlier and it's at almost an hour into an hour and a half print and working fine.So far. At least the belt doesn't seem to have any more problems so I guess it was the belt and not the motor. I'll probably try to stress it out tomorrow and see if the new belt fixed Twitchy's problem.

What do you do if the bearings DO dry up? 3 in 1 oil? Graphite?

Won't hurt to try a bit of 3 in 1, If they are crusty due to rust however then new ones will be needed. Dead cheap everywhere