Mesh bed compensation

Willo47

Hi , I have built a coreXY printer running a duet3d board with reprapfirmware.
I am having a problem with getting mesh bed compensation working.
I disable meshbed compensation with M561 and obtain Z probe height over various points on the bed then I activate meshbed compensation and the Z probe offsets remain identical to the disabled compensation. Has anyone been successful at getting meshbed compensaiton working. If so would you be able to share your setup code.
Thanks

Willo47

@bernardomattiucci
I too have problem with meshbed compensation not working despite trying every conceivable code.
My firmware did not come with a mesh.g file. Can anyone tell me what it consisted of

jay_s_uk

@Willo47 post an output of M122 when you think you have activated mesh compensation

droftarts

@Willo47 See https://docs.duet3d.com/en/User_manual/Reference/Gcodes#g29-mesh-bed-probe

Mesh.g

In RRF 3.2 and later, if G29 is commanded with no S parameter, then file sys/mesh.g is run if it exists.

In RRF 3.3 and later any parameters present are passed to mesh.g.

If sys/mesh.g is not present then the command behaves like G29 S0.

mesh.g is a specific macro called when mesh bed compensation (G29) is called for. It basically replaces bed.g, which was often set up to do the mesh bed compensation, but can now be used for other forms of bed compensation. You don't particularly need mesh.g as the mesh bed compensation can run on it's own, but it can be useful if you want to run other commands before and after. Here's mine:

; mesh.g
; called to perform bed mesh compensation via G29
;
; generated by RepRapFirmware Configuration Tool v3.2.3 on Thu Mar 18 2021 13:50:36 GMT+0000 (Greenwich Mean Time)
M561   ; clear any bed transform
G28 Z  ; home Z
G29 S0 ; probe the bed and enable compensation
G28 Z  ; home Z

Ian

droftarts

@Willo47 I've moved your posts from the other thread to this one, rather than revive a 2-year-old thread.

Ian

Phaedrux

@Willo47 said in Mesh bed compensation:

and the Z probe offsets remain identical to the disabled compensation

what exactly are you looking at here to determine it's not working?

The best way to see if it is having an effect is to print a first layer test print that covers the majority of the bed, either completely, or sparsely, and print it twice, once with the compensation active, and again without.

Willo47

@Phaedrux Hi Thanks for all of the replies. My printer has a print area of 500X500 mm. My prints are OK at the center and test prints are OK. When I print at the extremities is where I am having problems with first layer heights. My bed is well within +/- 0.5 mm level.
When I probe using G30 S-1 at the center I get a z return height of 2.4 mm which is what is entered into the config.g code. When I probe at the extremities is where I get different Z probe heights. The probe heights are identical with mesh bed leveling on or off.

Phaedrux

@Willo47 said in Mesh bed compensation:

When I probe at the extremities is where I get different Z probe heights. The probe heights are identical with mesh bed leveling on or off.

This isn't something that mesh compensation can solve. It sounds like you have some gantry sag. The compensation assumes that the XY gantry is flat over the entire area. You'd have to manually do G30 S-1 in a grid across the bed to map out what the variation is.