Withdrawal of support for 3, 4 and 5 point bed compensation


  • administrators

    Now that we have mesh bed levelling, I propose to withdraw support for the old 3, 4 and 5-point bed levelling for Cartesian/CoreXY printers, perhaps as soon as version 1.18. There are at least 2 bugs in that code, and I don't think it's worth fixing them and supporting two different types of bed compensation when the new mesh bed compensation is in most respects much better. The consequences will be:

    • When upgrading to latest firmware, if you are using 3, 4 or 5 point bed levelling (using either a bed.g file or M557 P commands), you will need to change the configuration to use mesh bed compensation instead. The simplest way of doing this is to define a probing grid in config.g using M557, then have the bed.g file home the printer if desired, deploy the probe (if needed), execute G29, and retract the probe (if needed).

    • If you were using 3-point compensation, the closest you can get is 4-point compensation.

    • If you were using 5-point compensation, the closest you can get is 4- or 9-point compensation.

    • The probe points must be on a regular grid.

    • The biggest problem will be if you were using H parameters on the G30 commands in bed.g on a Cartesian/CoreXY printer. To get equivalent results, you will need to run G29, then adjust the figures in the heightmap.csv file manually to account for the variation in trigger height.

    Does anyone object to this feature being removed - in particular, is anyone using H parameters on the G30 commands in a bed.g file for a non-delta printer?



  • For me personally this would be a retrograde steps but I know I'll be out voted.

    I don't actually use any form of bed compensation but I'll really miss the 3 point probing. I have a thick, flat, aluminium bed supported on 3 screws but constrained from twisting with linear guides. The screws are arranged with one in the front left corner, one in the front right and one in the centre rear. I use 3 point probing at each of the screw positions as an aid to initially setting the bed level and then periodically to check that it hasn't moved.

    If there is still a way that I can just probe the 3 points and report the values, but not apply any compensation, I'd be happy.

    Ian



  • They don't frequently post here, but I know of at least two people using cartesians that use the 3 point probing - it's fast and accurate enough. I can find out what they think about switching to a grid. Doubt they use height offsets.


  • administrators

    Thanks to both of you for your feedback. Perhaps I'll just remove 5-point probing? It doesn't work very well anyway, because if 4-point isn't good enough, the chances are you need 9-point because you have errors at the centres of at least 2 of the sides of the bed as well a sat the centre, e.g. because the X axis is sagging. Removing 5-point probing would eliminate one of the bugs that I'm not especially keen to spend time fixing.



  • I'm a little new, so take my input with a grain of salt, but if your bed is square, 4 point should be very simple to run with the grid if you enter the probing area as the size of the bed(?). So that feature is kinda supported twice, unless your bed is rectangular.



  • @3dprinting:

    I'm a little new, so take my input with a grain of salt, but if your bed is square, 4 point should be very simple to run with the grid if you enter the probing area as the size of the bed(?). So that feature is kinda supported twice, unless your bed is rectangular.

    The thing is, the best way to mechanically level a bed is by using 3 points - 1 fixed and the others adjustable. If you use 4 point (mechanical) levelling you run the risk of imparting a twist to the bed. So it's useful to be able to probe the bed adjacent to each of the 3 levelling screws - not to apply any software compensation but simply to report the height at each point so that any differences can be adjusted out mechanically.



  • @DC42,

    David, just a thought but if you introduce 2,3 or 4 Z motor bed levelling then I guess it'll be necessary to probe 2, 3 or 4 points? That being the case, then I'd be happy to use that if it had a check and report but no adjust feature built in. So 3 or 4 point levelling with an additional "check only" feature in place of 3 or 4 point compensation would work for me. HTH
    Ian


  • administrators

    Yes, I could leave the option for probing points and reporting the height errors in the firmware, but just remove the actual compensation.



  • @dc42:

    Yes, I could leave the option for probing points and reporting the height errors in the firmware, but just remove the actual compensation.

    That would be fine for me. Obviously other users may have different views.


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