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UM3 active levelling fails after firmware upgrade

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Dear all,


we are running several UM3 and UM2+ at out laboratory. Today i decided to update the firmware on one of the UM3 printers. After the firmware update, the active levelling fails always with the message: 'difference between detected height of both printcores exceeds realistic value'


-> I tried to level the print bed several times manually: No change. After manual levelling he tries always another active levelling procedure which naturally fails.

-> I tried to lower the height of the print bed by turning the screws: No change

-> I tried both the stable and the experimental versions of the firmware.


The levelling starts nearly in contact with the plate. During active levelling the z-stepper keeps running until the stepping fail with a "click". Thus, the printcores are pushed upwards until the x-y-rods are bend.


Any idea?



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4 hours ago, mech-thkoeln said:

The levelling starts nearly in contact with the plate.

I think during manual leveling the total distance between the top and bottom of the buildplate has gone outside of specifications (there is an end to what we compensate for)


Can you:

  • Make sure that your buildplate bottom and top are approximately 14mm apart.
  • Then manual level again.
  • Then try again.
Edited by robinmdh

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Dear Robin,


if i tighten the screws nearly completely, the procedure works again. Thanks.

However, i would wish that the programming of active levelling is more robust. It seems that you do not check at the start of the procedure if the plate is nearly in contact with the plate. Or why not use the z-height of manual levelling as starting point.


If i use -for example- the "BuildTak FlexPlate" on this UM3 the start distance is again too tight and active levelling fails again.


Thanks for help.

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15 hours ago, mech-thkoeln said:

Or why not use the z-height of manual levelling as starting point.

While not too bad an idea, what happens then if you insert a new hotend cartridge and the printer fails active leveling?

The level is stored per hotend cartridge/position so that info would be gone at that point.

The detection range also isn't infinite, we have to start somewhere that doesn't make it take too long for everyone.


On the good side we've improved this a lot recently both speed and accuracy but I have no idea when those changes will come to the UM3


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10 hours ago, Potateo said:

I am also having this issue. After installing the Flexplate system, automatic leveling fails.

Note that the active leveling system is very sensitive. Most likely, the system is introducing some kind of "softness" in the system that the active leveling cannot handle. Which looks for the sharp transition of not touching the bed to touching the bed.

It has not been engineered with this upgrade in mind. And it was already complex enough to get working without this. (As far as I know, these upgrades are not officially supported, sorry)

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38 minutes ago, FalmouthLouis said:

What might be happening here, when I have done absolutely nothing but set up a new printing attempt?

Often there is a little blob/bit of plastic still stuck to the nozzle, that can effect the measurements but it's also slowly squished and pushed out of the way by repeated probes.


This can e quite frustrating, but cleaning the nozzles before a print can be a huge help.

(or after a print, but then let the cooldown happen at the end as this prevents oozing at the start of the next)

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