Autoleveling issues?

Hi folks. Prusa i3. Seeing this sometimes:

[i.imgur.com]

I have autoleveling enabled. It's calibrated. The bed is nearly level anyway. I did the z probe repeatability test and I'm getting 30 microns stdev all over the bed.

I also upgraded my servo from a plastic gear to a metal geared one, didn't seem to make too much difference.

Has anyone seen this before? Looks like a bug in the autoleveling firmware to me. Marlin release branch checked out last June.

Thanks!

This offset is adjustable in Marlin and in the slicing software. It looks like your photo shows a problem with upper layers, not just the first layer. A larger image would be awesome, and can be attached directly to your reply.

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-David

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The offset has been carefully tuned, and things do work sometimes. It just looks like autoleveling is not working properly sometimes. One corner is fine, the others are not:

[i.imgur.com]

So is there a bug in the 4 point Marlin autoleveling procedure?

Hmm I tried simply switching to 3 point autoleveling and that caused the print head to crash into my bed. Alrighty.

Can you take a photo of the extended z-probe (not triggered)?

Also, your print bed may be bowed or warped when it is heated. You can check this by heating the bed and using a ruler or other known straight edge to check the flatness of the heated surface. Just place it on edge diagonally and see if you can slide a piece of paper (post-it note, etc.) under any portion of the edge, then try the other diagonal.

The auto bed leveling algorithm doesn't account for warpage well, it just creates a virtually level plane instead of assuming your bed is completely flat and the geometry is square to the other axes...

---

-David

Find me online at:
Thingiverse
Instructables.com
LinkedIn
Facebook

Check out my FolgerTech Prusa i3 (plexi) at MindRealm.net

Ahhhhh ok well warpage certainly might be possible.

Let me check that and get back to you.

Thanks!!

Ok, so it looks like the bed might be bulging upwards in the middle compared with the edges. I remember it was difficult to get the bed installed on the bolts, it felt tight. Perhaps there was some warpage there.

I used my autoleveling probe to help me level the bed by hand. This seemed to make things better a little bit, but there are still areas that are too low and areas that are too high.

Currently using an m3 bolt and three nyloc nuts for each corner of the bed, no springs. The first nut holds the bed in place, the next nut rests on the carriage, and the last nut holds the whole thing to the carriage.

I bought a Folger 2020 recently that just uses a bolt, spring, and thumbscrew. I wanted to use nyloc nuts originally since I was having issues with the bed rattling loose when printing. I was also told that springs are a bad idea.

Should I maybe try the spring/thumbscrew method? Any other ideas?

Thanks!

Had a similar issue.

I'm perhaps over hardware'd here but, I have an aluminum heat spreader attached to the x-carriage at three points, one point in the rear is a fixed height, the two front points are adjustable with springs. The M3 screw is attached to the aluminum plate with nuloc nuts, then the spring, and under the x-carriage is another nyloc nut (I was having an issue where the regular screws loosened over time).

I have the PCB heater board separated from the aluminum plate with nylon standoffs (and a cork sheet for insulation) at all four corners. There is very little warpage here even at temperature. Then the obligatory borosilicate glass plate is held in place with binder clips.

I manually level the hell out of this once, autolevel with G32 S2 for finesse, and then leave it alone. This has produced a very reliably level bed that requires very little ongoing maintenance.

Quote
foul_owl
Ok, so it looks like the bed might be bulging upwards in the middle compared with the edges. I remember it was difficult to get the bed installed on the bolts, it felt tight. Perhaps there was some warpage there.

I used my autoleveling probe to help me level the bed by hand. This seemed to make things better a little bit, but there are still areas that are too low and areas that are too high.

Currently using an m3 bolt and three nyloc nuts for each corner of the bed, no springs. The first nut holds the bed in place, the next nut rests on the carriage, and the last nut holds the whole thing to the carriage.

I bought a Folger 2020 recently that just uses a bolt, spring, and thumbscrew. I wanted to use nyloc nuts originally since I was having issues with the bed rattling loose when printing. I was also told that springs are a bad idea.

Should I maybe try the spring/thumbscrew method? Any other ideas?

Thanks!

If you are essentially locking down all four corners of the heated bed, as it heats up and expands, it's extra length has got to go somewhere so it will bow up or down. With the springs installed, it can push outward on the corners, cocking the springs slightly but preventing the bowing. You could also enlarge the holes and keep your nylocks slightly loose to allow the plate to slide in the hole/bolt directions.