Mesh Bed Compensation Screwy

dc42

…
But after I ran the bed compensation I then went back to each probe point and dropped the Z to 0 over the piece of paper, at all points the paper was trapped until I lifted the nozzle 0.3mm. So I added:
G1 Z0.25
G92 Z0
into the bed.g before the G1 Z5 and now everything seems to be working, but I am really mystified why I have to push the the height up by 0.25 does anyone know?

What XY coordinates to you use when you home the Z axis, in homez.g and homeall.g?

GrodanB

@dc42:

I've just released firmware 1.18beta2 which includes fixes for mesh bed compensation when the head is outside the points actually probed. My thanks to ChristophPech for the fixes.

And thank you for the update. Will try a new first layer ASAP. Just need to get home from work first.

hairy_kiwi

I'm just about to flash 1.18beta2, but wanted to check where, if anywhere in particular, should homez.g and homeall.g be run?

I'm seeing very similar results with 1.18beta1 on a couple of points other people have raised:

Using 1.18beta1 and homing z in homez.g and homeall.g at the bed center, while printing a 50x50x1.8mm solid cube at the bed center:

during first layer, I needed to Baby step z to +0.3mm (i.e. one print layer height) to prevent the first layer being badly squashed, despite z-homing to be accurate to ±0.025mm (gauged with a piece of note paper, itself checked with a digital 0.001mm/0.00005" micrometer).
Initially I used z-taper of 3.0 mm (M376 H3.0) but didn't see any visible z motion during the entire print, so reduced it to M376 H0.6. That resulted in quite a coarse z-compensation motion in one corner, but only AFTER 0.6mm z-height:

The results above were achieved using the following 9-point height map:

RepRapFirmware height map file v1 generated at 2017-02-12 13:15, mean error -0.00, deviation 0.05
xmin,xmax,ymin,ymax,radius,spacing,xnum,ynum
25.00,165.00,15.00,155.00,-1.00,70.00,3,3
  0.011,  0.013, -0.023
  0.070,  0.064, -0.013
 -0.051,  0.018, -0.095

Just before 1.18beta2 was announced, I generated the following 25-point height map, checked a couple of times; deviation repeatability is within ±0.01mm. (I'll recheck this with 1.18beta2):

RepRapFirmware height map file v1, mean error 0.01, deviation 0.04
xmin,xmax,ymin,ymax,radius,spacing,xnum,ynum
25.00,165.00,15.00,155.00,-1.00,35.00,5,5
  0.011,  0.015, -0.007,  0.010, -0.026
  0.024,  0.053,  0.062,  0.041, -0.013
  0.073,  0.061,  0.059,  0.040, -0.011
  0.032,  0.051,  0.066,  0.040, -0.031
 -0.038, -0.036,  0.019, -0.049, -0.099

EDIT: pics added

dc42

If you are using mesh bed compensation and also using the Z probe to do Z homing, then you should Z home with the probe over a point that is on the grid. Otherwise the interpolated bed height at that point may not be exactly the same as the probed bed height, leading to a difference in the Z=0 position.

I guess it might help if there was a version of the G30 command that lets you specify an XY position to probe for Z homing, just like G29 does. Otherwise you will need to take account of the probe X and Y offset yourself.

GrodanB

Lets try this:
RepRapFirmware height map file v1 generated at 2017-02-13 20:49, mean error 0.15, deviation 0.08
xmin,xmax,ymin,ymax,radius,spacing,xnum,ynum
26.00,299.00,12.00,188.00,-1.00,16.00,18,12
0.017, 0.127, -0.015, 0.007, 0.127, 0.000, 0.055, 0.127, -0.010, 0.105, 0.127, -0.005, 0.092, 0.080, -0.062, 0.075, 0.010, -0.043
0.060, 0.012, 0.130, 0.037, 0.072, 0.185, 0.142, 0.127, 0.240, 0.137, 0.107, 0.235, 0.122, 0.127, 0.145, 0.057, 0.060, 0.112
0.062, 0.197, 0.100, 0.030, 0.180, 0.115, 0.137, 0.225, 0.125, 0.182, 0.240, 0.102, 0.122, 0.158, 0.117, 0.135, 0.148, 0.075
0.122, 0.182, 0.070, 0.175, 0.165, 0.110, 0.220, 0.117, 0.120, 0.275, 0.185, 0.117, 0.217, 0.150, 0.105, 0.190, 0.092, 0.060
0.182, 0.150, 0.077, 0.240, 0.178, 0.192, 0.237, 0.275, 0.180, 0.280, 0.277, 0.180, 0.342, 0.148, 0.142, 0.245, 0.137, 0.172
0.137, 0.297, 0.122, 0.172, 0.222, 0.168, 0.247, 0.270, 0.215, 0.270, 0.242, 0.212, 0.230, 0.220, 0.140, 0.232, 0.190, 0.125
0.120, 0.202, 0.205, 0.158, 0.250, 0.245, 0.165, 0.255, 0.295, 0.247, 0.287, 0.200, 0.155, 0.300, 0.320, 0.180, 0.307, 0.192
0.205, 0.115, 0.185, 0.222, 0.210, 0.267, 0.202, 0.232, 0.303, 0.332, 0.225, 0.275, 0.262, 0.160, 0.197, 0.158, 0.158, 0.180
0.135, 0.172, 0.178, 0.145, 0.265, 0.252, 0.172, 0.287, 0.188, 0.195, 0.280, 0.182, 0.230, 0.252, 0.135, 0.175, 0.257, 0.150
0.092, 0.140, 0.057, 0.145, 0.155, 0.125, 0.207, 0.142, 0.120, 0.280, 0.162, 0.140, 0.197, 0.152, 0.142, 0.200, 0.140, 0.155
0.070, 0.055, 0.037, 0.120, 0.107, 0.035, 0.142, 0.105, 0.142, 0.145, 0.097, 0.142, 0.142, 0.040, 0.148, 0.180, 0.075, 0.137
0.017, -0.003, -0.028, 0.037, 0.002, -0.053, 0.095, 0.057, -0.023, 0.110, -0.010, 0.010, 0.033, 0.012, 0.055, 0.053, 0.015, 0.050

Nope, this did not work… printed in the air... do not understand

Next try:

I do get the impression that there is some "overcompensation" done here…
I do not get the feeling when testing the bed that it is half a mm off but that is what the probe measures...

But this is much better.

pcsentinel

Hi DC42in answer to your question, re four point plane above, I use the first probe point for HomeZ and HomeAll

GrodanB

In the override-config.g there is three G31 lines.

T1 had a z compensation number but not the X an Y. Why? I have this in my config.g file… But I do not have the T1 set in that file...

This is from my setup:
M558 P1 X0 Y0 Z1 H3 F200 T4000 ; Smart IR Z probe, used for homing Z axis, dive height 3mm, probe speed 200mm/min, travel speed 5000mm/min
G31 X-25.19 Y7 Z2.3 P500

I trigger the override-config.g later in the config.g file thus overriding my previous setup...

This could be the root cause to my "overcompensation" problem.

Now the main problem is the fact that this override-config.g is automatically generated.

Will test to do what is not recommended and that is to update the file.

I have the Z probe that came with my E3D Bigbox. Is that a type T1 probe then?

Why can't I set the probe placement relative to each tool separately?

Why do I have a T3 and T4 G31 in my automatically generated file?

I got hopeful that is was Tool 1 probe offsets in each G31...

The more I read the less I seem to understand how this work...

CHP

@GrodanB

Why can't I set the probe placement relative to each tool separately?
Because it has nothing to do with the tool offsets. Think of the IR-sensor as if it it's own tool.

Also your measured bed-matrix looks very inconsistent. I had the same problem on my BigBox in the past, the reason was that the angle of the IR-sensor was not parallel to the bed. I couldn't even change the angle because the screws of the sensor mount have made some groves.

The "correct" bed-matrix on the BigBox should look mostly flat with a slight bulge upwards in the center (this is due to the sag of the smooth rods)

dc42

@GrodanB:

In the override-config.g there is three G31 lines.

T1 had a z compensation number but not the X an Y. Why? I have this in my config.g file… But I do not have the T1 set in that file...

This is from my setup:
M558 P1 X0 Y0 Z1 H3 F200 T4000 ; Smart IR Z probe, used for homing Z axis, dive height 3mm, probe speed 200mm/min, travel speed 5000mm/min
G31 X-25.19 Y7 Z2.3 P500

I trigger the override-config.g later in the config.g file thus overriding my previous setup...

This could be the root cause to my "overcompensation" problem.

Now the main problem is the fact that this override-config.g is automatically generated.

Will test to do what is not recommended and that is to update the file.

I have the Z probe that came with my E3D Bigbox. Is that a type T1 probe then?

Why can't I set the probe placement relative to each tool separately?

Why do I have a T3 and T4 G31 in my automatically generated file?

I got hopeful that is was Tool 1 probe offsets in each G31...

The more I read the less I seem to understand how this work...

Yes the IR sensor that came with the BigBox is a type 1.

Probe X and Y offset in the G31 command is relative to the head reference point, just like the G10 tool offsets. So you don't need a different probe offset for each tool. You can choose the head reference point wherever you like. If you have just one nozzle, then you would normally use the nozzle position as the head reference point. On my dual nozzle printer, I chose the head reference point to be mod way between the two nozzles.

RRF records separate G31 parameters for probe types 0 or 1 or 5, 3 and, 4 so that you can use more than one Z probe. Running M500 saves all of them. That's why you get G31 commands for probe types that you have not actually configured.

I just tried changing the probe offset by sending a G31 command with X and Y parameters, then I ran M500. The new offsets were correctly shown in the G31 command in config-override.g. Perhaps you last ran M500 when before you included X and Y offsets in your G31 command?

GrodanB

@CHP:

@GrodanB

Why can't I set the probe placement relative to each tool separately?
Because it has nothing to do with the tool offsets. Think of the IR-sensor as if it it's own tool.

Also your measured bed-matrix looks very inconsistent. I had the same problem on my BigBox in the past, the reason was that the angle of the IR-sensor was not parallel to the bed. I couldn't even change the angle because the screws of the sensor mount have made some groves.

The "correct" bed-matrix on the BigBox should look mostly flat with a slight bulge upwards in the center (this is due to the sag of the smooth rods)

How did you fix it?

That is the way it looks when making a five point bed level… And one other thing that is weird: the five point bed level shows the corners approximately at the same height... But not the mesh level.

I have not the borosilicate glass but the PEI aluminum bed from Clever3D. So it MIGHT be less flat... But then again does not look that way when checking with a straightedge.

So test for tonight : somehow get the sensor more level... Is the one that is sold on duet3D better (although not more square) ?
I will try to set the bed height relative the nozzle with the bed level screws then somehow get the sensor more square to that...

Then I'll change my offset to the middle point of the print heads... (and verify that the new offset is recorded in the file after m500.)

CHP

@GrodanB
(I have the Clever3D bed too, but not the black one, the metallic one)
I made this horrible IR-sensor mount: https://drive.google.com/file/d/0B-DBgmDdShYnSkRBVXBBMklWanc/view?usp=sharing
It's good for testing the influence of the angle but only a temporary measure before I switch to IDEX. You can easily misalign it by touching it the wrong way, also it only fits the pro-hybrid carriage with volcano.

Additionally my bed.g script turns off the lights before measuring and turns them back on after, but I'm almost sure that doesn't matter.

hairy_kiwi

@dc42:

If you are using mesh bed compensation and also using the Z probe to do Z homing, then you should Z home with the probe over a point that is on the grid. Otherwise the interpolated bed height at that point may not be exactly the same as the probed bed height, leading to a difference in the Z=0 position.

I guess it might help if there was a version of the G30 command that lets you specify an XY position to probe for Z homing, just like G29 does. Otherwise you will need to take account of the probe X and Y offset yourself.

Thanks for that.

I like your idea if I understand correctly: it would extending the G30 command to include XY motion AND take into account any already specified z-probe XY offset?

I've just had a play with 1.18beta2 and - unrelated to it - by chance discovered I have an issue with the reflectance of the window glass sitting on my heated bed PCB: The 'bunker' in the middle of the mesh in the image below is most probably the result of (unintentionally) z-probing over the center of the Prusa MKII-style PCB - exactly where the thermistor hole is located. This may explain my previously reported issue where I needed 0.3mm of baby stepping to correctly set z0.

Next, after performing G30 in a random location using the following macro (use with caution and best deleted when done to prevent inadvertently crashing tool or z-probe):

; Z-PROBE macro to check random locations:
G91                ; relative mode
G1 Z4 F200         ; raise head 4mm to ensure it is above the Z probe trigger height
G90                ; back to absolute mode
G30                ; lower head, stop when probe triggered and set Z to trigger height

I then tried moving the head away from that location and in some areas, within less than a millimeter of X or Y travel, observed the z-probe LED (trigger height indication) would extinguish. It seems the probe is being affected by the white screenprint on the PCB, and the darker area provided by the thermistor hole. Is this feasible? I thought I'd read that plain glass was capable of providing sufficient reflection for the IR z-probe? I'll try placing a piece of black paper under the glass when I get some, but it does make me wonder if the distinctly-patterned bed meshes other people are generating is the result of subtle changes in reflectance due to minute influences of the weave of a PCB material or machining marks on tooling plate, for example. Any thoughts?

I have probed the bed in the past with a digital 0.01mm indicator and the shape otherwise generally agrees with the generated bed mesh, except for the center divet or bunker:

GrodanB

Just started on my test work… Disassembled the z-probe... and low and behold:

That cannot be good if it is sensitive to not being square…

Will now re-assemble it and try again... after standing the part up.

And I also tested that the M500 stores the value.

I also moved the "center" to midpoint of print heads.
G31 T1 P500 X-44.2 Y7.0 Z2.53

Is this correct?

The probe is -44.2mm to the left of the center of the tools... when printing I still do not understand HOW the compensation is done... T0 (left tool) is at -38 when right tool (T1) is at zero. X that is... So when T1 is printing the probe is -63.2 to the left of the printing area... But the compensation says -44.2...

But the config.g has the code above... but the G31 T1 seem not to be updated by that... so just running the G31 above seemed not to get the T1 entry updated in the override file.
But when adding the G31 manually to T1 and then a M500 it was stored...

SOOOO close... but no cigar...

Hard to see when the depth of field is not so good but the duet is pressing hard against the bed in the front left and less to the right

This is the mesh level result:

Still bumpy but I assume better…
Why is this five point leveling UNDER the grid?

I have not printed between these mesh leveling…

I give up for now... do not understand this...

Dougal1957

Yep had this happen a few times after failed prints where a rats nest has caught them straighten them up and re-measure the Z Offset value and carry on printing.

CHP

@GrodanB
If your right tool is at zero then the sensor is relative to that:
G31 T1 P500 X-63.2 Y7.0 Z2.53

From your picture it looks like the IR LED is bend (but I'm not sure, it could be just the odd angle of the photo)

By "adjusting the angle of the IR sensor board" I meant through the 2 screws at the top which are connected to the carriage. If you look at the plastic under the screws there might be some depressions from the screws in which case you can't change the angle anymore so the part needs to be reprinted.

GrodanB

Yes, fixed the IR sensor…

So the 90 degree is not in Y but in Z then...?

And 0,0 is different for each tool when looking from the sensors point of view...

T1
G1 X0 Y0 Z3

Set the right tool at 0,0

T0
G1 X0 Y0 Z3

Set the left at the same place...

Therefore my confusion...
When I use T1 the compensation is not relative that tool... but place in between...

Today I have leveled (mechanically) the bed so that the same spacer was used between the print head and the bed corners, that should mean that the bed is parallell to the print head... But this is the duet view of that...

Same result as always… check the base relative the bottom. Same distans left and right...

Re adjusted the sensor so that it is parallell i Y with the bed... 90 as square as I can get it in Z.

OHH... Just had a thought... Could i be that I have to much of the left side so that the sensor is so close to the edge that it see the edge of the bed and therefor makes the left side lower...

First test: Put a tape so that I shield the sensor from the light that is from the left.... No change... just as "bad".
Second test: Move the outer limits of the test 25mm in on the bed... No change... just as "bad". But now it seem buggy...

GrodanB

Is there a bug in mesh leveling?

I use this after homing all axis:

M557 X50:300 Y25:175 S25

And the mesh leveling start @ X == 113 not 50.
Testing the lates 1.18beta3 with the new web interface 1.15b2.

But looking at the first point is seem to think it is @50,25…

Picture taken during mesh leveling changing Y position… this is X113 according to the display but the result file seem to think this is X50...

Here is my latest marco for meshleveling:
T0 ; select first hot end
G91 ; Relative coordinates
G1 Z4 F6000 ; Lower bed to avoid hotend dragging in bed.
G1 X-350 Y-240 F3000 S1 ; move up to 240mm in the -X and -Y directions until the homing switches are triggered
G1 X6 Y6 F600 ; move slowly 6mm in +X and +Y directions
G1 X-10 Y-10 S1 ; move up to 10mm in the -X and -Y directions until the homing switches are triggered
G90 ; Absoulte coordinates
G1 X150 Y100 F3000 ; Go to middle and probe the Z axis…
G30 ; Home Z-axis
M557 X50:300 Y25:175 S25 ; Bed level from X26Y12 to X299Y188 in 16mm increments 16x11 points (176)
G29 S0 ; Auto Bed Level and create report
M374 ; Save calibration grid
G1 X70 Y200 F3000 ; Dock after bedlevel. Move first in front of docking notch
G1 X70 Y235 F3000 ; Dock after bedlevel
M500

Now testing mesh level with 1.18beta2 and see if it does the same thing...

dc42

It's because you have a large Z probe offset in the X direction. The grid points are where the probe is, not where the head is.

GrodanB

Ahh ok so I should remove this when probing? (nice, always like to find that it is my fault… makes the fix easier...)

or use T1 when mesh leveling...

Will test... setting to T1 seems much better....

Will use the Beta3 after this... if that is "recommended" (I'll use the beta2 otherwise.)

Thanks for the good work... One day I hope to understand this...

GrodanB

Last thought before I give up…

Looking at this there seem to be a constant that is NEVER removed regardless how much I try

(X0,Y0) is the closest corner (when controlling tools))

One end is pressed too hard against the nozzels and the other is pressed to little. ALWAYS. Same side also.

This is the one constant thing I have. When it is at its best this is how it gets…

Looking at the height map:
RepRapFirmware height map file v1 generated at 2017-02-18 21:41, mean error -0.13, deviation 0.10
xmin,xmax,ymin,ymax,radius,spacing,xnum,ynum
50.00,300.00,25.00,175.00,-1.00,25.00,11,7
-0.385, -0.383, -0.290, -0.342, -0.288, -0.253, -0.247, -0.195, -0.200, -0.280, -0.263
-0.317, -0.263, -0.233, -0.120, -0.098, -0.088, -0.108, -0.130, -0.178, -0.240, -0.175
-0.245, -0.175, -0.160, -0.132, -0.135, -0.053, -0.080, -0.085, -0.043, -0.080, -0.035
-0.217, -0.178, -0.152, -0.070, -0.033, 0.000, 0.013, -0.020, -0.035, 0.037, -0.027
-0.168, -0.150, -0.110, -0.003, 0.003, 0.043, -0.003, 0.030, -0.037, -0.003, -0.040
-0.172, -0.175, -0.090, -0.108, -0.172, -0.045, -0.020, -0.057, -0.045, -0.043, 0.010
-0.273, -0.247, -0.205, -0.155, -0.158, -0.130, -0.085, -0.112, -0.145, -0.135, -0.105

The side that has to much "compensation" is -0.385 and the side that has to little is -0.263. (assuming that the 0,0 point is the upper left...)

Now I do not print in the extreme parts of the bed... I print in the middle. And there it is more flat. BUT looking at the print (this is an old shown before but see little point in making the same picture today). It seems that the compensation is strange... the one that is close is not at all pressed (supposed to be 70% layer height) and the one that is far from the nozzle is pressed hard...

This makes me wonder if my printer has the same coordinates for X and Y when it comes to the Probe and tools...? Can I control that, or more precise can I have made a set-up mistake that causes the duet to switch on or more axis?

Because it makes little difference what I do... I always get the same result... (that is somehow good... consistency)