Ender 3 Z-limit now unreliable - possible causes and solutions?

4

I had a couple of recent nozzle/bed crashes, so I now frequently do a manual bed levelling. I do these while the bed is heated to allow for expansion.

Today i found, after levelling, a subsequent print could vary from having too much clearance (paper moves very freely) to less than no clearance (which left deep grooves in the bed as per the photo).

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What are the possible causes? Is it just a dodgy Z-limit switch or something else? What solutions are available and at what cost? Obviously an ABL seems essential now, but requires a lot of hardware and setup.

Update

Just happened again so here are some more details.

Printing PLA this time. - Preheated bed. - Levelled bed all over and got a very good raft. - Print failed later so aborted. - Restarted the same print. - Nozzle gouged out a uniform depth trench around print perimeter.

The uniform depth of the gouge indicates a problem related to Z-axis only as bed remains flat and level, but height is out.

Gone Coding

Posted 2018-11-10T12:35:06.103

Reputation: 418

I doubt it's the z-limit switch. I'd think two things: you aren't leveling your bed correctly; you've got some unaccounted for slop in your setup which allows the bed to come out of calibration after you've done your calibration. – Pᴀᴜʟsᴛᴇʀ2 – 2018-11-10T13:27:03.270

How flat is the bed/sticker on the bed? Have you put a metal ruler on its side over the bed to check the level? – 0scar – 2018-11-10T13:31:39.517

did the physical switch moce? – Trish – 2018-11-10T13:36:25.120

@Paulster2: I have done over 100 successful prints, prior to this issue, so do have some clue about levelling the bed :) I am interested in what could cause such a large variation. Initially I thought it was temperature as I switched to ABS at the time, but it now varies from one print to the next. – Gone Coding – 2018-11-10T20:37:06.923

@Oscar: I do a 9 point check and get almost the same tension on a sheet of paper throughout. I was lucky to get a very flat bed (aside from the gouges now present of course!) – Gone Coding – 2018-11-10T20:38:31.550

@Trish: I will check the bolts on the z-limit, but that would mean it has moved both up and down and up again. Thanks – Gone Coding – 2018-11-10T20:39:49.343

can you check if the bed is flat? distortion could be an issiue – Trish – 2018-11-11T16:20:19.207

@Trish: added more details. Bed is flat and level before and after this occurs. – Gone Coding – 2018-11-11T22:30:06.630

did you test the physical reliability? – Trish – 2018-11-12T10:42:57.143

@Tris: The machine is a month old and rock solid. Specifically physical reliability of what? The z-axis is the slowest moving axis, controlled by the limit switch only, hence my suspecting that is the cause. – Gone Coding – 2018-11-12T15:38:48.333

I had similar issues on my XY-100 once - the Z-axis limit switch was indeed not tightened correctly, and would tilt a bit. You may want to try reducing the Z-axis homing speed to prevent it from exerting too much force, or tightening the switch more. – towe – 2018-11-13T11:10:16.803

I purchased a couple of spare Ender 3's and will update various parts in turn to see what the cause is. The metal trigger on my Z-limit switch seems a little floppy sideways, but I am also starting to suspect the bed springs have lost their springiness. – Gone Coding – 2018-11-21T10:49:53.963

Check this black plate sticker that is attached to bed. Take it off and look at bottom side. Mine one swelled up in some places. Replaced with piece of mirror. – filimonic – 2018-11-21T17:21:52.810

1@filimonic I have the removal bed version and also a borosilicate glass bed. The glass is perfectly flat and the standard removable is dipped ever so slightly in the middle, but the difference is huge when it goes wrong. As you can see from the photo the trench it digs is quite uniform depth. That's why I keep coming back to the z-limit switch. I have a spare switch now so will try that next. – Gone Coding – 2018-11-25T18:30:51.253

It happened to me too, the z limit changed from one print when it was working well to the other where it destroyed completely the magnetic bed... I didn't change any parameter between those two prints so I don't understand what happened! – Lembeu – 2019-05-29T05:59:21.170

bought a used ender 3 2 days ago, same issue. I just tried levelling it 5 times nad every times it went very flat on the Z-stop or raised up again by 2-3 millimeters, randomly different, regardless of where the bar was at prior to levelling. it's either the connections in the z-motor/rod or the z-stop which is supposed ot be failsafe. ill check the motor connection. – aliential – 2020-01-02T21:49:54.830

Answers

1

I've just bought an Ender 3 Pro and as a guess I would look at the Z axis stepper motor to see if it is not holding position once it stops... the stepper motor has power on it all the time it is stopped to hold it in position.

I would check the plug that feeds power to see if it is damaged or not making good contact.

window

Posted 2018-11-10T12:35:06.103

Reputation: 41

1

Similar issue happened to coworker's Maker Ultimate. I'm gonna go out on a limb and assume that your Z-stop is a little mechanical switch, and there's an M3 screw going through part of the Z carriage that pushes said switch. Check to see how much force it takes to rotate said screw. There's a lot of vibration happening in a 3d printer, and it takes surprisingly little vibration to make a threaded part do weird things, including making it back out against gravity if conditions are right. Redo your Z gap paper test, get everything lined up, and then slap a dab of blue loctite on the screw to make sure it doesn't move during your next print. See if that fixes your problem.

Nach0z

Posted 2018-11-10T12:35:06.103

Reputation: 826

0

This was killing me on mine. My problem wasn't the z-axis, it was the x-axis arm. On the right side, opposite the extruder gear, it had a lot of give (wobble). I could level my bed four times before starting a print and would still have problems, especially with the nozzle making deep grooves in the magnetic bed. The way it messed up was inconsistent as well, making it hard to troubleshoot.

I changed out the bedsprings, got a glass bed instead, changed out the extruder gear and Bowden tube; I was ready to give up.

How to fix the wobble, if that's your problem, if there's a lot of give / vertical movement on the right side of the arm:

You have to take the whole arm off. First, take the top bar off, remove the four screws. Second, disable steppers so you can take the x-axis off completely. I removed the cables once I had taken it off. Third, there's a plate with two holes to get to two screws - make sure these are tight! This is where the wobble was coming from. Four, reassemble and double-check. For me, the give was reduced drastically.

A video tutorial for help. There are English subtitles.

Akexis

Posted 2018-11-10T12:35:06.103

Reputation: 1

Are you the original poster on a second account? – Davo – 2020-03-20T14:54:36.390

No, I just thought my issue was also my z-axis and came across this several times in trying to figure things out and figured I'd post my solution in case it helps anyone else. – Akexis – 2020-03-21T15:52:57.527