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Is G81 no longer supported?  

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Clutchplate
(@clutchplate)
New Member
Is G81 no longer supported?

I  use the Octoprint plugin called 'Prusa Leveling Guide' by Scott Rini to level my MKS3S+ bed (I have the Nylock mod). I just upgraded the machine to MK3.5 with the kit (keeping the Nylock mod), and now the plugin doesn't work anymore. Looks like it issues a G80 to do mesh leveling and then G81 to get the results. I tried sending G80 in the terminal and the G81 and while the leveling finished correctly, G81 did not send the offset matrix. In fact I got a 'unknown command'. Is this expected?

- Lutz

Posted : 10/03/2024 4:27 am
John Weaver
(@john-weaver)
Eminent Member
RE: Is G81 no longer supported?

I need to try again, but the one time I did I couldn't even get G80 to work.  It made a horrible grinding noise so I hit the reset button.  I had the silicone mod before and it worked great.  No problems with the clips I put in from the kit, I was just wanting to see how level it was. 

Posted : 11/03/2024 12:55 am
Hiigara
(@hiigara)
Active Member
RE: Is G81 no longer supported?

Honnestly. Got the nylon lock and the Plugin with octoprint on my mk3.

I remove it when upgrading to mk3.5 to ensure i got the designed product at first.

First layer are perfect. The mode is not really needee anymore.

Posted : 14/03/2024 6:49 am
Clutchplate
(@clutchplate)
New Member
Topic starter answered:
RE: Is G81 no longer supported?

Yeah, I ended up removing the Nylock mod and using the new brackets. I did have to install BedVisualizer to make sure that it was level. I had to manually adjust one of the two Z-motors since the bed wasn't level left to right.... but yeah, first layers are perfect now.

Posted : 14/03/2024 8:13 am
Campblor
(@campblor)
Eminent Member
RE: Is G81 no longer supported?

Agreed, these expansion joints do the trick perfectly. 

Posted : 15/03/2024 2:53 pm
John Weaver
(@john-weaver)
Eminent Member
RE: Is G81 no longer supported?

 

Posted by: @campblor

Agreed, these expansion joints do the trick perfectly. 

 

How are they supposed to work exactly?  I've never seen it explained.

 

Posted by: @hiigara

Honnestly. Got the nylon lock and the Plugin with octoprint on my mk3.

I remove it when upgrading to mk3.5 to ensure i got the designed product at first.

First layer are perfect. The mode is not really needee anymore.

I had the silicone tube mod on my MK3S+ and I went with the expansion joints for the same reason as you.  You're using Octoprint to get the bed level measurements right?  I'm not using Octo right now even though I had it on the MK3S. 

Any other way to get the necessary info to level the bed besides pronterface and G80/G81?

Posted : 15/03/2024 10:16 pm
Campblor
(@campblor)
Eminent Member
RE: Is G81 no longer supported?

Not entirely sure but I fitted them and my prints are coming out just fine. I haven't done a full bed level test print but if anything the printer feels more robust.

As for what they do I assume they expand with heat and keep a uniform expansion over the whole thing? Then the ABL takes over the rest. Either way it prints good. 

Posted : 20/03/2024 11:15 pm
bzz
 bzz
(@bzz)
Member
RE: Is G81 no longer supported?

Has anyone figured out how to get the bed leveling data from the MK3.5?  As OP mentioned, G81 no longer appears to be supported.  The new heated bed brackets are not working nearly as well as the nylock mod I had in place before the 3.5 upgrade. 

Posted : 18/06/2024 6:26 am
digitalbrush
(@digitalbrush)
Active Member
RE: Is G81 no longer supported?

Was this ever solved? I am trying to fix my bed leveling currently, and am running into Unknown command: "G81".

So far my search has brought me to trying G28, G29, and then G29 T. 

G28 to auto home.

G29 to probe.

G29 T to print out the mesh table to the screen.

But I don't understand if I have to format the mesh table in some way. I tried copying and pasting the mesh table into the online bed visualizer at https://i.chillrain.com/index.php/3d-printer-auto-bed-leveling-mesh-visualizer/, but it doesn't look right.

I'm hoping someone will see this and post the solution,

 

Posted : 30/07/2025 2:19 am
digitalbrush
(@digitalbrush)
Active Member
RE: Is G81 no longer supported?

After rediscovering that the mk3.5s still has a USB port that the computer can connect to, but it's USB-C now, I was able to connect it to my computer and run Pronterface. The output from Pronterface when executing the Auto Home command from the LCD menu shows that the printer uses G28. Then starting "Mesh Bed Leveling" from the LCD touchscreen menu shows that it uses G29 to execute that command instead of G80.

So I think I'm on the right track. "G29" to start the mesh bed probing, and "G29 T" to get the mesh bed matrix.

I then found a mesh bed visualizer online to interpret the numbers for me... though I'm still not sure if I'm doing this right. It would be great if I could do it this way instead of having to print calibration squares and wait for them to finish and adjust each time.

Posted : 30/07/2025 8:23 am
digitalbrush
(@digitalbrush)
Active Member
RE: Is G81 no longer supported?

After rediscovering that the mk3.5s still has a USB port that the computer can connect to, but it's USB-C now, I was able to connect it to my computer and run Pronterface. The output from Pronterface when executing the Auto Home command from the LCD menu shows that the printer uses G28. Then starting "Mesh Bed Leveling" from the LCD touchscreen menu shows that it uses G29 to execute that command instead of G80.

So I tried "G29 T" to get the mesh bed matrix and it seems to have worked. I'm not used to interacting with this data, so I used an online converter to help me look at the data and visualize the bed. Link: https://bbbenji.github.io/PMSBLM/

It's also part of the website for the "Prusa Mini Silicone Bed Leveling Mod." Link: https://github.com/bbbenji/PMSBLM

This github also has instructions for getting the leveling data using the G29 codes which seems to be working in place of the missing G81 code.

Copied and pasted directly from the site above, credit to bbenji for the info:

Make sure you replace your steel sheet

G28 ; home all
M104 S170 ; set extruder temp for bed leveling
M140 S60 ; set bed temp
M109 R170 ; wait for extruder to reach temp
M190 S60 ; wait for bed temp

Once the temperature has reached the target, input the GCode below, depending on your firmware version.

FW < 5.1.0

G29 ; mesh bed leveling
G0 Z25 F720 ; raise Z
M18 ; disable motors

FW >= 5.1.0

G29 ; Probe mesh
G29 T ; Display probed mesh
G0 Z25 F720 ; raise Z
M18 ; disable motors

Now, wait for the mesh leveling to complete. You should see output something like this:

FW < 5.1.0

0 -0.048 -0.040 -0.066 -0.035
1 -0.040 -0.030 -0.044 -0.010
2 -0.065 -0.050 -0.061 -0.047
3 -0.347 -0.029 -0.045 -0.155

FW >= 5.1.0

        0       1       2       3       4       5
5 | +0.251  +0.165  +0.054  +0.082  -0.055  -0.063
  |
4 | +0.262  +0.164  +0.065  +0.012  -0.060  -0.133
  |
3 | +0.249  +0.162  +0.076  -0.058  -0.065  -0.073
  |
2 | +0.221  +0.152  +0.084  +0.009  -0.021  -0.051
  |
1 | +0.317 [+0.221] +0.125  +0.030  +0.005  -0.020
  |
0 | +0.359  +0.290  +0.166  +0.051  +0.031  +0.001
        0       1       2       3       4       5

Copy the results and paste them into the text area on the Prusa Mini G29 converter page found here: https://bbbenji.github.io/PMSBLM/.

I'm still not sure if I'm doing this right, but I think I may be on the right track.

 

Posted : 30/07/2025 9:05 am
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