Delta calibration failed

[dc42]

Your dial gauge probe is offset from the nozzle, which means that if you have a geometric error that causes effector tilt (very common in delta printers) then it won't give you an accurate reading of nozzle height. My suggestions:

1. Measure the FSR trigger height at various points on the bed, not by using the dial probe but but dropping the nozzle until it just grips a piece of paper, sending G92 Z0, raising the nozzle a few mm and using G30 S-1 to measure the trigger height. This is to check that the FSRs are giving you consistent trigger heights.

2. If the FSR trigger height is consistent, after calibration run G29 to generate a height map. Then the difference between the dial gauge reading and the height map is caused by effector tilt. See https://duet3d.dozuki.com/Wiki/Calibrating_a_delta_printer#Section_Make_sure_your_build_is_accurate for common causes.

[Viald]

Thank you for quick help.

I already do such calibration for FSRs.

As you can see in my bed.g, I have commented all the H parameters to do new tests. because even with H parameters I have bad results.

G30 P0 X-86.60 Y-50.00 Z-99999 ;H-0.04	; Pos 1 X tower
G30 P1 X0.00 Y-100.00 Z-99999 ;H0.054	; Pos 2 between X-Y towers
G30 P2 X86.60 Y-50.00 Z-99999 ;H-0.055	; Pos 3 Y tower
G30 P3 X86.60 Y50.00 Z-99999 ;H.023	; Pos 4 between Y-Z towers
G30 P4 X0.00 Y100.00 Z-99999 ;H0.019	; Pos 5 Z tower
G30 P5 X-86.60 Y50.00 Z-99999 ;H0.058	; Pos 6 between Z-X towers
G30 P6 X-43.30 Y-25.00 Z-99999 ;H0.008	; Pos 7 X tower
G30 P7 X0.00 Y-50.00 Z-99999 ;H0.027	; Pos 8 between X-Y towers
G30 P8 X43.30 Y-25.00 Z-99999 ;H0.018	; Pos 9 Y tower
G30 P9 X43.30 Y25.00 Z-99999 ;H0.023	; Pos 10 between Y-Z towers
G30 P10 X0.00 Y50.00 Z-99999 ;H0.044	; Pos 11 Z tower
G30 P11 X-43.30 Y25.00 Z-99999 ;H0.053	; Pos 12 between Z-X towers
G30 P12 X0 Y0 Z-99999 S9		; center and auto-calibrate 6 factors

I followed as well all the calibration documentation including the possibility of mesh correction.
Here is the height map result:

As I already said on my first post, rotating le glass by 180° gives quite the same height map. So I guest that this comes from the frame and not the bed...

Even with G29 S1 in the config.g, I still not be able to print big part, this is why I decided to replace the duct by a dial gauge probe to try to understand what's wrong.

Just for fun, I think there is a bug in the mesh process. Changing the mesh grid to 9 points gives me this strange result.

Thanks

[dc42]

Looks like you have 6 points around the periphery, 6 points half way, and 1 in the centre. You may get better results with more peripheral points. I use 9 around the periphery, 3 half way, and the centre.

Yes, that height map looks odd.

[Viald]

Ok, I will give a try with this settings.
Thanks

[Viald]

What is the maximum number of points we can set for probing ?
Does it make sense if I use the maximum ?

[dc42]

Maximum points in bed.g is 32. Using more points helps if your height map shows substantial errors in places well away from your existing probe points.

[Viald]

Hello !
Using this awesome tool http://escher3d.com/pages/wizards/wizardbed.php , I set 10 points on edge, 3 half way and 1 in the centre.

G30 P0 X0.00 Y110.00 Z-99999 H0
G30 P1 X70.71 Y84.26 Z-99999 H0
G30 P2 X108.33 Y19.10 Z-99999 H0
G30 P3 X95.26 Y-55.00 Z-99999 H0
G30 P4 X37.62 Y-103.37 Z-99999 H0
G30 P5 X-37.62 Y-103.37 Z-99999 H0
G30 P6 X-95.26 Y-55.00 Z-99999 H0
G30 P7 X-108.33 Y19.10 Z-99999 H0
G30 P8 X-70.71 Y84.26 Z-99999 H0
G30 P9 X0.00 Y55.00 Z-99999 H0
G30 P10 X47.63 Y-27.50 Z-99999 H0
G30 P11 X-47.63 Y-27.50 Z-99999 H0
G30 P12 X0 Y0 Z-99999 S9

Autocalibration result:

G32
Calibrated 9 factors using 13 points, deviation before 0.075 after 0.067

Height map result

This gives different result, but that still sounds not very good

[Dougal1957]

@viald I notice that you are using S9 on the last line of your G30's in the bed.g file I think you would do better if you changed that to S6 or S8 S7 and S9 will auto adjust the arm lengths for a best fit and we know that isn't always optimum as I am sure DC will explain.

Just my thoughts.

Doug

[Viald]

Thank you Doug.
Here is the result with S6

Unfortunately, almost the same.

[Dougal1957]

@viald that's not actually auto calibration tho that is the result of mesh bed compensation!!

[Viald]

You are right, this is the height map calculation after the auto calibration I did
What information do you what about the autocalibration ?

[Viald]

Finally, I set 19 points, 12 on edge, 6 half way and 1 in the center. I also add the trigger height for each point in real condition (head at 210° and bed at 65°)

G30 P0 X0.00 Y110.00 Z-99999 H-0.092
G30 P1 X55.00 Y95.26 Z-99999 H-0.024
G30 P2 X95.26 Y55.00 Z-99999 H-0.005
G30 P3 X110.00 Y0.00 Z-99999 H-0.073
G30 P4 X95.26 Y-55.00 Z-99999 H0.03
G30 P5 X55.00 Y-95.26 Z-99999 H0.011
G30 P6 X0.00 Y-110.00 Z-99999 H0.026
G30 P7 X-55.00 Y-95.26 Z-99999 H0.029
G30 P8 X-95.26 Y-55.00 Z-99999 H0.015
G30 P9 X-110.00 Y-0.00 Z-99999 H-0.039
G30 P10 X-95.26 Y55.00 Z-99999 H-0.011
G30 P11 X-55.00 Y95.26 Z-99999 H-0.072
G30 P12 X0.00 Y55.00 Z-99999 H-0.05
G30 P13 X47.63 Y27.50 Z-99999 H-0.015
G30 P14 X47.63 Y-27.50 Z-99999 H-0.009
G30 P15 X0.00 Y-55.00 Z-99999 H0.014
G30 P16 X-47.63 Y-27.50 Z-99999 H0.010
G30 P17 X-47.63 Y27.50 Z-99999 H-0.025
G30 P18 X0 Y0 Z-99999 S6

What do you think about the trigger heights ? Is it necessary to add it ?

Here the autocalibration log

Calibrated 9 factors using 19 points, deviation before 0.067 after 0.062

The same using S6

Calibrated 6 factors using 19 points, deviation before 0.065 after 0.064

I don't know what this information means, what could be the conclusion ?
As Doug said, what is the difference between S6/7/8/9 in G30 command ?

Thank you.

[Viald]

It seems to be good

[Viald]

In fact, the first layer is still no so good, so I still try to improve the precision of the Delta.

I have completely disassembled the delta and check each part.
I have rebuild it, calibrated again and again for in fact having the same poor calibration result

G32
Calibrated 6 factors using 19 points, deviation before 0.068 after 0.067

The default seems to be symmetrical and I have absolutely no idea where it comes from.

I switched the connection of the stepper and end switch on the board, X ->Y, Y->Z and Z->X, and did another calibration.
I supposed that the height map will also rotate 90°, actually not, the height map has exactly the same symmetrical default in the same direction

What could it mean ? This Delta makes me crazy

[oliof]

check out http://boim.com/DeltaUtil/CalDoc/Calibration.html for possible reasons for deviation.

[Viald]

Thanks. I already read this interesting information, but none of the effects exposed are precisely mine. It seems that my issue is a combination of multiple error effects.

I think, I should start with the rod length effect. I should precisely manually measure each of them, and check is they are equal.

But they are about 290mm long and my caliper is not large enough

[dc42]

@Viald, have you read https://duet3d.dozuki.com/Wiki/Calibrating_a_delta_printer#Section_Make_sure_your_build_is_accurate ? A circular (bulls-eye) spirit level mounted on the effector will show up many types of geometric error that can cause height variations.

[Viald]

Yes I read it several times. The bulls-eye spirit level is a very good idea, If the result is not correct, I think It won't be easy to interpret the feedback.
If the bubble is fixed during effector mouvements, the issue clearly comes from the bed, at the opposite it could comes from too many things.

I'm currently trying to compare rods length with a micrometer. I'm going step by step, because I'm lost.

[Viald]

As my caliper is not large enough to measure the magnetic arms length, I made this tool to compare the length.

I took one arm length as a reference and compare it to others, here is the result:

1/ Ref (0.00)
2/ +0.02
3/ -0.03
4/ -0.04
5/ 0.00
6/ 0.00

I guess that this is good enough, and my issue does not come from the arms length.

Arms are good

To check if the autocalibration is correct, I measure as precise as possible the length in 3 parts

The sphere diameter is 9.41, so the arm length is 213.64 + 42.55 + 42.53 - 9.41 = 289.31
The autocalibration (S7) always find a longer length around 291.786

M665
Diagonal 291.786, delta radius 171.632, homed height 229.294, bed radius 114.0, X -0.180°, Y -0.129°, Z 0.000°

So I decided to fixe the real length in config.g and did multiple S6 autocalibration
That's the best I can have:

G32
Calibrated 6 factors using 19 points, deviation before 0.078 after 0.077

M665 L289.300 R170.748 H229.244 B114.0 X-0.167 Y-0.125 Z0.000
M666 X0.135 Y0.152 Z-0.287 A0.30 B0.19

@dc42 I bought circular spirit level, I first checked the bed level which is perfect.
Check the video https://dai.ly/k4fXd07BAdjzOztaR39

Bed is good

Then I put the level on the effector, adjusted its level at X0 Y0 and move to each tower, below is the result:

The video link https://dai.ly/k50wYDzWkYziSLtb1Nv

What ever the Z position is, I have exactly the same levelling, and moving along the Z axe, the levelling does neither not change.

But, actually the effector is tilting when it's close to each tower. For sure this is the issue, but where does it come from ?

Thanks for your help.

[Viald]

And Voilà !!!!
Look at this That's much better compare to the previous one :))

G32
Calibrated 7 factors using 19 points, deviation before 0.022 after 0.021

M665
Diagonal 289.536, delta radius 170.580, homed height 229.474, bed radius 114.0, X -0.089°, Y -0.175°, Z 0.000°

And the rod length is quite the same compare to measurement I did.

The distance between balls of the carriage and balls of the effector was not the same. The max difference was 0.9mm
The carriages of my printer have a screw to tight them much or less on the V-slot profile. But when you tight them you change the distance between the 2 balls, which cause a major issue on the geometry of the printer.

I still have a small tilt effect on the effector, but I think that the precision should be now enough to print large parts.
I'll give a try and let you know.