Question regarding M671 in relation to bed leveling

p40whk

I'm setting up a modified Prusa I3 with dual Z-motors and have the following code set for defining the drives:

M584 X0 Y1 Z2:4 E3 ; Two Z motors connected to driver outputs 2 and 4 (plug Jumper into ZB on Drive 2)

I've read the descriptions of the G-code for M671 as well as the page on "Bed leveling using multiple independent Z motors" however, I don't understand what the values are measured against.

Is the X and Y coordinates of the leadscrews in relation to nozzle when X and Y are homed? If so then measuring from X is simple as the lead screws are already on that plane but I'm not sure how to figure the Y coordinates as both Lead screws should be the same distance from the Zero location of Y?

So if I am reading this right should the code look as follows:

M671 X-71.0:344.0 Y-53.0:-53.0 S0.5 ; leadscrews at rear right and rear left

Firmware Electronics: Duet WiFi 1.02 or later
Firmware Version: 2.01(RTOS) (2018-07-26b2)
WiFi Server Version: 1.21
Web Interface Version: 1.21.2-dc42

grizewald

If your origin point is the front left of the bed (which I believe is the default), then the Y coordinates of the lead screws will be positive from the origin point at 0, 0.

My bed only goes up and down, and my lead screws are at: M671 X-46:346 Y226:226 S2

Both of the X coordinates are outside the bed itself.

p40whk

Actually, my origin point is the right rear of my print bed, at least this is how I view it.

Here's a photo of what I'm referring to and how I think the M671 line should read:

Photo Link

dc42

I can't see your photo, looks like it is private.

The leadscrew positions are relative to wherever (0, 0) is. As you have just two leadscrews, one at each end of the X axis, the Y coordinates don't matter much. I suggest you use the middle of the Y axis as the Y coordinate of both leadscrews, and also probe using the same Y coordinate. This will minimise the effect of any Y axis twist that your machine may have.

p40whk

@dc42 Thanks for the reply,

Not sure why my photo isn't visible, I had it as public in Google Photos, tried it in Flicker and can't seem to embed it from there so I added a link instead. please take a look at let me know if I'm reading you correctly.

Thanks

dc42

The M571 X coordinates look OK, but I suggest Y150:150 or wherever the middle of the printable Y axis is. Although I think it shouldn't make any difference.