is my bed crooked?

[Macwolf]

I use three Z axes for the automatic bed alignment on my printer.
but the height map shows something strange.
I've attached the config and bed

config.g bed.g

[Phaedrux]

Does the order of the pivot points listed in M671 match the order of the motors listed in M584?

What are the results shown when doing a G32? If you run it more than once does it get better or worse?

If the order doesn't match, you can actually be adding twist to the bed rather than correcting it.

https://docs.duet3d.com/User_manual/Connecting_hardware/Z_probe_auto_levelling

[droftarts]

@Macwolf If you are confident the bed is flat, and your machine is a CoreXY or Cartesian machine where the nozzle/probe moves in XY and the bed moves in Z, this may be showing that Y rails are not running parallel. It could even be that the frame is twisted.

Ian

[Dad003]

does look like it may be warped ... if it level with 3 axis there so much it can do ...

[Macwolf]

@Phaedrux
Does the order of the pivot points listed in M671 match the order of the motors listed in M584?
Yes
What results are displayed on a G32? Does it get better or worse if you do it more than once?
the result is always accurate
G32
Leadscrew adjustments made: 0.261 -0.106 0.064, points used 3, (mean, deviation) before (0.090, 0.112) after (0.000, 0.000)

after
Leadscrew adjustments made: -0.020 0.035 0.036, points used 3, (mean, deviation) before (0.016, 0.017) after (0.000, 0.000)

If the order doesn't match, you can actually add a twist to the bed instead of correcting it.
how does it work?

[Macwolf]

this machine is a tool changer with a 3 belt drive, the bed is 6 mm finely milled cast aluminum plate, I cannot check whether this is straight. but I think so.

to test I put a glass plate on the bed which is on 2 parallel pegs and the result is the same

that's on the borosilicate board

[deckingman]

@Macwolf As @droftarts has pointed out, that height map is a classic sign that the bed isn't "tram" with the XY gantry rails. It's something that I've been banging on about for years but nobody listens. When you have 3 lead screws arranged to form a triangle, and you probe near each lead screw attachment point, the 3 points of the bed describe a plain. When you level the bed, that plain becomes parallel with a plain described by the bottom fixings of the 3 lead screws. BUT, if the XY gantry rails are not absolutely parallel with those two plains, then the bed is level but not "tram" with the XY gantries. What you must now do is adjust the frame. One way of doing it is, after the bed has been levelled, probe the 3 points diametrically opposite the lead screws but only measure the height. This will tell you where the high and low points of the XY gantries are. I did a YouTube video on how to get a bed both level and tram. I'm using my phone right now but when I get to a computer, I'll post a link.

[Macwolf]

@deckingman hence the question of whether the bed is crooked or something else, the Y rail (CBC) is mounted on aluminum, according to the height map the aluminum should be warped. if it's not the bed.

[deckingman]

@Macwolf Not necessarily warped, but certainly not parallel with the plane of the bed. The most common reason is that the printer frame isn't truly square.

[droftarts]

@Macwolf given that your bed is 6mm milled aluminium, it is probably flat. Use a straight edge, like a metal ruler, to check. Otherwise, like @deckingman says, it is a teaming issue. You can check if the frame is square by measuring the diagonals of each side, top and bottom. It may be out of square due to the cuts of the aluminium not being square. When you have checked that, slacken the bolts of the Y rails and see is there’s enough adjustment in them to remove the twist.

Ian

[deckingman]

@droftarts Looking at the scale for the height map would indicate an error of +_0.25mm and ideally we want this less than 0.1mm. I would doubt my ability to accurately measure a frame of a few hundred mm diagonally to within 0.1mm (I don't have vernier calipers that big)

Here is the video I made a couple of years ago showing how I do the levelling and tramming with a dial gauge. with https://www.youtube.com/watch?v=H9O1r46Izn8

[Macwolf]

Thanks for the answers, meanwhile the highest value is 0.3mm, I drove off the top of the top plate

with a dial gauge, the Y rail is at 1-2/100. the bed is warped from the middle of 3/10.

Thanks Markus

[oliof]

@Macwolf you measured that with the bed still installed on the frame, right?

Please try to adjusting the back right corner of the frame right Y rail) by .1mm upwards and remeasure.