Issues with what looks like layer alignment

Hello lulzbot community.

I’m pretty new to all this having gotten a lulzbot mini 2.0 back in November and only recently an enclosure and a box to keep my filament dry. I’ve recently begun to print a lot mroe than I used to as I’m printing out parts for a MPCNC.

I’ve run into an issue where parts of some layers are not aligned with the rest of the layer. I’m a new poster so I can only upload one image.

Hopefully above you can see my issue. Above are 2 prints I did back to back, but increasing the printing temperature between prints with issues at identical locations as far as I can tell. I contacted support as I was expecting I should do some sort of hardware maintence but they suggested it was the settings I have for my material and to ask on the forums, but I expected a more chaotic issue if I had bad settings.

Anyway, I’m printing hatchbox PLA, I can’t recall my higher temps, but I’m using the Village Plastics PLA preset in cura 3.6.21 on windows, with a layer height of 0.38. I’ve got the nozzle that came with my mini 2.0 on it still, 0.5mm nozzle.

Thanks for any advice anyone can give me! Let me know if I forgot to include some details.

edit: the image I uploaded is upside down, in case that is important.

This may be a belt tension issue or backlash compensation. It appears to be on just one axis. Since the shifts are in the same places on both parts it suggests that it’s not random per se… but based on the slicer path.

In other words … suppose it’s on the X axis… if the head moves to a specific position (say X=100.0mm) but travels from left to right … will it arrive in exactly the same spot if it travels to that same position by traveled from right to left?

Make sure the belt on the appropriate axis (x or y) isn’t loose. You can also adjust the backlash compensation in firmware. (The TAZ Workhorse & Pro have a “calibration cube” on the corner of the build plate designed to let the printer self-detect and dial in backlash compensation … but I don’t think the Mini has a calibration cube.)

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Hey thanks for the suggestion. Its my Y and I’m working on figuring out how to tighten the belt in my spare time. My allen keys that are large enough to fit the screws for the belt don’t fit into the nook between where the belt is clamped and the bed carriage.

I’ll post back when I’ve done it and tried a new print.

Check belt tension and also check backlash compensation settings in Marlin.

If you think the belt is loose, see section 4 of this page: https://ohai.lulzbot.com/project/final-mechanical-assembly-mini2/mini-2/

That page shows how to tension the belt (basically you flip the printer over to access the belt).

Backlash Compensation:

Another factor that controls this is ‘backlash compensation’. The idea is that all mechanical machines have some amount of “backlash”. The idea is that if you told the printer to move the printhead 25.00mm ‘back’ (in the Y axis) and then told the printhead to move 25.00mm ‘forward’ (in the Y-axis) you might think you’d be back where you started … but if you actually measured this precisely … you’d probably find that it’s not quite exactly back where it started. This is the backlash.

For example, the backlash compensation on my TAZ Workhorse the Y-axis backlash compensation is set to 0.18.

The M425 command can be used to view or adjust backlash compensation. You can use the ‘Console’ feature of Cura to do this. (You’ll find it in the “Monitor” panel).

See: https://marlinfw.org/docs/gcode/M425.html

If you type M425 on it’s own (don’t supply any parameters) then it will report current settings.

e.g.:

M425

If you type M425 along with any parameter then it will change that setting.

E.g.:

M425 Y0.15

would set the backlash compensation on the Y-axis to 0.15mm.

Note that the change will revert if you power-cycle the printer. To save it permanently (so that it is saved even though a power-cycle) you’ll need to use the M500 command.

Also… it is possible to measure and enter backlash compensation… but not actually use backlash compensation. This is controlled via the “F” parameter on the M425 command. If F=0 then it means backlash compensation is disabled (you may see values… but the printer wont actually use them). F=1 means that backlash compensation is enabled at 100%.

The TAZ Workhorse and TAZ Pro have a “calibration cube” which electronically measures backlash and sets the correct values. I don’t think the Mini 2 has this cube or auto-backlash measurement. This means you’ll need to measure and adjust the values manually.

Best Regard,
Tim