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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).

enter image description here

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.

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  • $\begingroup$ 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. $\endgroup$ – Pᴀᴜʟsᴛᴇʀ2 Nov 10 '18 at 13:27
  • $\begingroup$ 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? $\endgroup$ – 0scar♦ Nov 10 '18 at 13:31
  • $\begingroup$ did the physical switch moce? $\endgroup$ – Trish Nov 10 '18 at 13:36
  • $\begingroup$ @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. $\endgroup$ – Gone Coding Nov 10 '18 at 20:37
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    $\begingroup$ @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. $\endgroup$ – Gone Coding Nov 25 '18 at 18:30
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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.

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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.

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