A few question about Mesh bed compensation
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I have a BLtouch and read alot of guide about how to set up mesh bed compensation, but i feel i don t understand how it behave.
First this is exactly what i do with my duet2:
I set Probe triger height to 0 and reboot.
Next i center and lower my hotend to the point of just touching the bed.
I do a G92 Z0 and a G1 Z10
I then move my probe to the exact same center point and do a G30 S1, 3-4 times and calculate the average (is there a way to automate that?) I enter the value in the config file as my Ztrigerheigth and reboot.
Finally i home all, then move probe to middle at Z10 do a G30 and G29 to get heightmap saved.Here s a few question:
-The generate heightmap show - and + value of what? The trigerheight or the G30 value or something else.
-If i edit the heightmap manually +value means the nozzle will get closer to the bed and -value nozzle get further away. Or the opposite ?
-Does compensation round up or down number? ie for a value of 0,013 does it translate to +0.01 move or a +0.02 move to the stepper motor? How precise can it be?
-My bed is X220 Y220 but i can only probe from X30X175 and Y20Y200, what happen to the area with no data. Does it keep the last compensate point height or does it go back to a non compensate height (in my case G30 height)?
-Last question. Can G28 probe each point multiple time and take the average. I don t probe before every print i would prefer to do a long and accurate probing session and use the heighmap saved rather than do it every print and get a occasional bad reading from the Bltounch.
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@Negetem said in A few question about Mesh bed compensation:
(is there a way to automate that?)
https://forum.duet3d.com/topic/22139/macro-for-automatic-calibration-of-bl-touch
@Negetem said in A few question about Mesh bed compensation:
The generate heightmap show - and + value of what? The trigerheight or the G30 value or something else.
Plus or minus to the Z0 point that you set when you did the G30. 0 is the reference and the rest of the bed is either above or below (or equal) that point.
@Negetem said in A few question about Mesh bed compensation:
-If i edit the heightmap manually +value means the nozzle will get closer to the bed and -value nozzle get further away. Or the opposite ?
The values in the heightmap mean that + values are above 0 and - below it. So if you edit them to make them more + you're saying that point is higher above 0.
@Negetem said in A few question about Mesh bed compensation:
-My bed is X220 Y220 but i can only probe from X30X175 and Y20Y200, what happen to the area with no data. Does it keep the last compensate point height or does it go back to a non compensate height (in my case G30 height)?
It tries to extrapolate what the height might be. This is usually ok for a short distance on the edge where the probe can't reach. If you know you have a sudden high or low spot you could do a manual probing (m558 P0) where you can use the nozzle to touch down those areas manually and avoid the probe offset, then add those newly probed areas to your heightmap from the bltouch. Or just try to reduce the probe distance to the nozzle.
@Negetem said in A few question about Mesh bed compensation:
-Last question. Can G28 probe each point multiple time and take the average. I don t probe before every print i would prefer to do a long and accurate probing session and use the heighmap saved rather than do it every print and get a occasional bad reading from the Bltounch.
Do you mean G28 or G29? Either way the behaviour of the probing moves is defined in M558 and G31 in config.g and gives you some options for how to customize it.
At the very least you should do a G28 before each print and your Z homing should use G30. Then once Z0 has been set with that G30 you can either run G29 to create a new mesh, or G29 S1 to load the last saved mesh.
https://duet3d.dozuki.com/Wiki/Gcode?revisionid=HEAD#Section_M558_Set_Z_probe_type
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Thank you Phaedrux for the reply.
Going back to the Heightmap, and the example of + value.
The 0 reference, is the height the compensation is trying to maintain to print. IF it s positive then the compensation will lower the hotend the amount it has been save at that XY position in a radius i guess half the size between each point. Correct?For my last question, Yeah i meant G29. But seeing the involve code to automate the calibration of Bltouch. It would take some coding effort to do the same for the G29 command. I'll put that to rest for now.