Auto Calibration Woes - converging and diverging values



  • Hi all,
    I am currently calibrating my 1.2m tall delta. I had a problem with slipping of rail carriages. I lubricated them to solve the issue. Thanks to Andres and DJ.

    For calibration, I measured a trigger height of 1.42mm and added appropriated corrections in the bed.g file. I deleted the config-override.g file and ran these calibrations. During calibration, the values converge and then diverge. I mean the deviations will reduce till .06mm and then suddenly will shoot to 0.130 mm and gradually reduce till 0.06mm.

    One thing to note here is that my PEI surface was a bit scratched when I decided to try printing when I had lubrication issues. Here is my pei bed photo:

    I have a big trigger height variation due to this issue. The trigger height at various points are:

    P0 1.44
    P1 1.49
    P2 1.26
    P3 1.49
    P4 1.64
    P5 1.29
    P6 1.47
    P7 1.66
    P8 1.66

    Below are my G32 values copy pasted from the console and you can see how it converges and diverges.

    Calibrated 6 factors using 10 points, deviation before 0.227 after 0.096
    3:41:50 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.294 after 0.128
    3:39:58 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.270 after 0.084
    3:38:28 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.269 after 0.124
    3:37:00 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.225 after 0.130
    3:35:29 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.126 after 0.089
    3:33:55 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.104 after 0.064
    3:32:24 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.245 after 0.142
    3:30:52 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.230 after 0.137
    3:29:24 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.158 after 0.139
    3:27:56 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.173 after 0.087
    3:25:50 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.256 after 0.099
    3:24:21 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.198 after 0.114
    3:22:52 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.141 after 0.080
    3:21:08 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.146 after 0.111
    3:19:37 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.213 after 0.104
    3:18:08 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.335 after 0.105
    3:16:38 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.274 after 0.106
    3:15:10 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.280 after 0.163
    3:13:41 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.224 after 0.124
    3:12:13 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.263 after 0.120
    3:10:43 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.251 after 0.106
    3:09:14 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.219 after 0.096
    3:07:38 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.126 after 0.070
    3:06:07 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.154 after 0.016
    3:04:37 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.175 after 0.079
    3:03:08 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.505 after 0.221
    2:53:35 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.254 after 0.101
    2:51:58 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.252 after 0.096
    2:50:24 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.291 after 0.121
    2:48:50 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.275 after 0.153
    2:47:13 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.181 after 0.074
    2:45:38 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.425 after 0.188

    Here is my config.g
    ; Configuration file for Duet WiFi (firmware version 1.17)
    ; executed by the firmware on start-up
    ;
    ; generated by RepRapFirmware Configuration Tool on Thu Jun 01 2017 14:36:55 GMT+0200 (W. Europe Daylight Time)

    ; General preferences
    M111 S0 ; Debugging off
    G21 ; Work in millimetres
    G90 ; Send absolute coordinates…
    M83 ; ...but relative extruder moves
    M555 P2 ; Set firmware compatibility to look like Marlin

    ;*** The homed height is deliberately set too high in the following - you will adjust it during calibration.
    M665 L360.310 R158.653 H510 B115.0 X0 Y0 Z0; Set delta radius, diagonal rod length, printable radius and homed height
    M666 X0 Y0 Z0 A0.00 B0.00; Put your endstop adjustments here, or let auto calibration find them
    M208 Z0 S1 ; Set minimum Z

    ; Endstops
    M574 X2 Y2 Z2 S0 ; Define active high microswitches
    M558 P1 X0 Y0 Z0 H5 F360 T2400 ; Set Z probe type to unmodulated, the axes for which it is used and the probe + travel speeds
    G31 P500 X16 Y-20 Z1.42 ; Set Z probe trigger value, offset and trigger height
    M557 R115 S20 ; Define mesh grid

    ; Drives
    M569 P0 S0 ; Drive 0 goes forwards
    M569 P1 S1 ; Drive 1 goes forwards
    M569 P2 S1 ; Drive 2 goes forwards
    M569 P3 S0 ; Drive 3 goes forwards
    M350 X16 Y16 Z16 E16 I0 ; Configure microstepping without interpolation
    M92 X160 Y160 Z160 E837 ; Set steps per mm
    M566 X1200 Y1200 Z1200 E1200 ; Set maximum instantaneous speed changes (mm/min)
    M203 X6000 Y6000 Z6000 E800 ; Set maximum speeds (mm/min)
    M201 X600 Y600 Z600 E500 ; Set accelerations (mm/s^2)
    M906 X1400 Y1400 Z1400 E900 I60 ; Set motor currents (mA) and motor idle factor in per cent
    M84 S30 ; Set idle timeout

    ; Heaters
    M143 S285 ; Set maximum heater temperature to 285C
    M305 P0 T100000 B3950 C0 R4700 ; Set thermistor + ADC parameters for heater 0
    M305 P1 T100000 B4388 C0 R4700 ; Set thermistor + ADC parameters for heater 1
    M307 H1 A204.0 C112.3 D4.0 B0

    ; Tools
    M563 P0 D0 H1 ; Define tool 0
    G10 P0 X0 Y0 Z0 ; Set tool 0 axis offsets
    G10 P0 R0 S0 ; Set initial tool 0 active and standby temperatures to 0C

    ; Network
    M550 PSM3D ; Set machine name
    M552 S1 ; Enable network
    M587 Ssamrudh P"samrudh2013" ; Configure access point. You can delete this line once connected
    M586 P0 S1 ; Enable HTTP
    M586 P1 S0 ; Disable FTP
    M586 P2 S0 ; Disable Telnet

    ; Fans
    M106 P0 S0 I0 F500 H-1 ; Set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
    M106 P1 S1 I0 F500 H1 T20 ; Set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
    M106 P2 S1 I0 F500 H-1 ; Set fan 2 value, PWM signal inversion and frequency. Thermostatic control is turned off

    ; Custom settings are not configured

    ; Miscellaneous
    M501 S1
    T0 ; Select first tool

    Here is my bed.g

    ; bed.g
    ; called to perform automatic delta calibration via G32
    ;
    ; generated by RepRapFirmware Configuration Tool on Thu Jun 01 2017 14:36:55 GMT+0200 (W. Europe Daylight Time)

    G28 ;Home all the axes

    ; Clear any bed transform
    M561

    ; Probe the bed at 6 peripheral and 3 halfway points, and perform 6-factor auto compensation

    ; Before running this, you should have set up your Z-probe trigger height to suit your build, in the G31 command in config.g.

    ; bed.g file for RepRapFirmware, generated by Escher3D calculator
    ; 10 points, 6 factors, probing radius: 60, probe offset (16, -20)
    G30 P0 X0.00 Y60.00 Z-99999 H0.02
    G30 P1 X45.39 Y26.20 Z-99999 H0.05
    G30 P2 X36.95 Y-21.33 Z-99999 H-0.16
    G30 P3 X0.00 Y-44.13 Z-99999 H0.07
    G30 P4 X-50.62 Y-29.23 Z-99999 H0.22
    G30 P5 X-51.96 Y30.00 Z-99999 H-0.13
    G30 P6 X0.00 Y30.00 Z-99999 H0.05
    G30 P7 X14.26 Y-8.23 Z-99999 H0.24
    G30 P8 X-21.42 Y-12.36 Z-99999 H0.24
    G30 P9 X0 Y0 Z-99999 S6

    ; Use S-1 for measurements only, without calculations. Use S4 for endstop heights and Z-height only. Use S6 for full 6 factors
    ; If your Z probe has significantly different trigger heights depending on XY position, adjust the H parameters in the G30 commands accordingly. The value of each H parameter should be (trigger height at that XY position) - (trigger height at centre of bed)

    Hope someone can see the problem that I could not see. I am not sure how to proceed from here. Any tips would be useful.

    Best Regards,
    Vasan


  • administrators

    I suggest you copy bed.g to a macro. In the copy, change the S parameter on the final G30 command to S-1. That will allow you to probe the same points and report the height errors without changing the calibration. Make a second copy, and in that one also remove the G28 homing command. Then you can try the following:

    • Run the second copy (the one without the homing command) several times and see how the results compare. If they vary a lot, then either you have inconsistent motion or you are not getting consistent trigger heights from the Z probe.

    • If the that did give you consistent results, run the first copy several times. If that doesn't give consistent results, then you have one or more homing switches with inconsistent trigger heights.

    • If both of those give consistent results, then perhaps the issue is that when the calibration changes, the probe points move slightly, and if they move on or off scratches that may be changing the probe trigger height. If that is the case, then I suggest either a new sheet of PEI or a different Z probe that doesn't mind the scratches. The Duet3D delta effector with buiult-in nozzle contact probe should be available about 4 weeks from now and may be suitable for your printer (you would also need to upgrade to magnetic arms to use it, or else make adapters for your existing arms). Failing that, the 1.19beta7 firmware version includes a manual calibration facility, although it's a bit clunky to use until support for it has been added to DWC and PanelDue, which should happen during next week.

    HTH David



  • Hi David,
    Thanks for your reply. I did the testing according to your suggestions. I tried the bed file posted with and without trigger height corrections (H Parameter in G30). Now, I have four results:
    (1) Second Bed file without homing and no trigger height corrections
    (2) Second Bed file without homing and trigger height corrections
    (3) First Bed file with homing and no trigger height corrections
    (4) First Bed file with homing and trigger height corrections

    Output for (1) - No Homing and No trigger height corrections

    9:28:41 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.233 -0.188 -0.405 -0.156 0.821 0.136 0.130 -0.301 0.307 0.169, mean 0.074, deviation from mean 0.338
    9:27:56 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.233 -0.157 -0.355 -0.131 0.809 0.174 0.136 -0.289 0.319 0.213, mean 0.095, deviation from mean 0.326
    9:27:12 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.239 -0.138 -0.343 -0.138 0.827 0.192 0.148 -0.301 0.332 0.176, mean 0.099, deviation from mean 0.330
    9:26:30 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.208 -0.132 -0.349 -0.119 0.821 0.174 0.155 -0.289 0.319 0.194, mean 0.098, deviation from mean 0.324
    9:25:28 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.220 -0.144 -0.361 -0.138 0.827 0.211 0.148 -0.283 0.307 0.207, mean 0.099, deviation from mean 0.330
    9:24:34 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.114 -0.132 -0.355 -0.125 0.852 0.180 0.136 -0.289 0.313 0.213, mean 0.091, deviation from mean 0.331
    9:23:23 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.208 -0.132 -0.399 -0.156 0.840 0.155 0.142 -0.289 0.307 0.169, mean 0.084, deviation from mean 0.336
    9:22:45 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.220 -0.176 -0.380 -0.163 0.859 0.186 0.136 -0.289 0.319 0.207, mean 0.092, deviation from mean 0.344
    9:21:24 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.183 -0.126 -0.380 -0.119 0.846 0.180 0.136 -0.283 0.319 0.213, mean 0.097, deviation from mean 0.333
    9:20:23 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.220 -0.151 -0.343 -0.131 0.834 0.167 0.142 -0.289 0.307 0.194, mean 0.095, deviation from mean 0.328
    9:19:46 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.214 -0.144 -0.349 -0.125 0.840 0.167 0.142 -0.289 0.307 0.201, mean 0.096, deviation from mean 0.329
    9:18:57 PMM98 P0:/macros/Bed Measurement
    Bed probe heights: 0.220 -0.144 -0.349 -0.113 0.834 0.199 0.148 -0.295 0.313 0.169, mean 0.098, deviation from mean 0.328

    Output for (2) - No Homing and with trigger height corrections

    9:40:54 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.081 -0.238 -0.233 -0.226 0.582 0.272 0.067 -0.535 0.048 0.163, mean -0.002, deviation from mean 0.300
    9:40:14 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.088 -0.244 -0.239 -0.226 0.564 0.266 0.080 -0.554 0.073 0.157, mean -0.004, deviation from mean 0.301
    9:39:32 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.088 -0.244 -0.233 -0.226 0.576 0.272 0.086 -0.529 0.073 0.176, mean 0.004, deviation from mean 0.300
    9:38:54 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.081 -0.244 -0.233 -0.220 0.576 0.272 0.086 -0.529 0.073 0.169, mean 0.003, deviation from mean 0.299
    9:38:09 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.200 -0.238 -0.245 -0.233 0.595 0.266 0.080 -0.535 0.073 0.169, mean 0.013, deviation from mean 0.310
    9:37:08 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.225 -0.194 -0.208 -0.195 0.589 0.310 0.092 -0.529 0.079 0.207, mean 0.038, deviation from mean 0.306
    9:36:30 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.181 -0.194 -0.226 -0.201 0.582 0.291 0.073 -0.535 0.073 0.219, mean 0.026, deviation from mean 0.304
    9:35:55 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.206 -0.232 -0.233 -0.220 0.582 0.304 0.086 -0.529 0.067 0.213, mean 0.024, deviation from mean 0.310
    9:35:08 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.181 -0.238 -0.233 -0.226 0.564 0.310 0.098 -0.529 0.079 0.207, mean 0.021, deviation from mean 0.307
    9:33:20 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.231 -0.244 -0.226 -0.233 0.589 0.297 0.092 -0.535 0.067 0.201, mean 0.024, deviation from mean 0.314
    9:32:47 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.231 -0.176 -0.208 -0.195 0.576 0.297 0.080 -0.529 0.073 0.194, mean 0.034, deviation from mean 0.301
    9:32:10 PMM98 P0:/macros/Bed with height corrections
    Bed probe heights: 0.200 -0.232 -0.239 -0.233 0.607 0.272 0.086 -0.535 0.061 0.213, mean 0.020, deviation from mean 0.314

    Output for (3) - Homed and No trigger height corrections

    10:51:27 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.011 -0.257 -0.480 -0.212 0.590 0.067 0.048 -0.370 0.213 0.094, mean -0.032, deviation from mean 0.296
    10:49:26 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.017 -0.257 -0.486 -0.238 0.577 0.055 0.023 -0.401 0.226 0.101, mean -0.042, deviation from mean 0.300
    10:47:50 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.005 -0.251 -0.480 -0.212 0.602 0.086 0.048 -0.395 0.207 0.107, mean -0.029, deviation from mean 0.302
    10:46:17 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.030 -0.257 -0.480 -0.256 0.621 0.061 0.023 -0.408 0.188 0.088, mean -0.045, deviation from mean 0.307
    10:44:04 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.005 -0.251 -0.474 -0.231 0.552 0.074 0.042 -0.389 0.213 0.107, mean -0.036, deviation from mean 0.291
    10:42:19 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.005 -0.244 -0.480 -0.219 0.559 0.074 0.036 -0.395 0.219 0.113, mean -0.034, deviation from mean 0.294
    10:40:51 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.017 -0.257 -0.486 -0.238 0.559 0.061 0.023 -0.414 0.201 0.101, mean -0.047, deviation from mean 0.296
    10:38:45 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.017 -0.263 -0.493 -0.256 0.577 0.074 0.030 -0.414 0.188 0.082, mean -0.049, deviation from mean 0.301
    10:37:17 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.005 -0.263 -0.486 -0.238 0.559 0.067 0.023 -0.401 0.207 0.088, mean -0.045, deviation from mean 0.295
    10:34:06 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.005 -0.251 -0.486 -0.244 0.565 0.067 0.030 -0.395 0.201 0.113, mean -0.041, deviation from mean 0.296
    10:31:35 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.005 -0.251 -0.480 -0.219 0.559 0.061 0.048 -0.401 0.238 0.107, mean -0.034, deviation from mean 0.296
    10:29:37 PMM98 P0:/macros/Bed no height corrections
    Bed probe heights: -0.024 -0.251 -0.474 -0.250 0.646 0.086 0.017 -0.408 0.182 0.082, mean -0.039, deviation from mean 0.311

    Output for (4) - Homed and With trigger height corrections

    10:22:22 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: -0.031 -0.294 -0.314 -0.320 0.395 0.204 -0.027 -0.648 -0.058 0.088, mean -0.101, deviation from mean 0.286
    10:18:41 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: -0.012 -0.301 -0.314 -0.320 0.407 0.197 -0.033 -0.635 -0.052 0.094, mean -0.097, deviation from mean 0.286
    10:16:57 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: -0.019 -0.282 -0.301 -0.295 0.376 0.216 -0.008 -0.616 -0.021 0.113, mean -0.084, deviation from mean 0.277
    10:15:01 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: -0.044 -0.307 -0.320 -0.326 0.407 0.197 -0.045 -0.648 -0.052 0.082, mean -0.106, deviation from mean 0.288
    10:13:19 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: -0.031 -0.294 -0.314 -0.301 0.357 0.191 -0.008 -0.635 -0.021 0.113, mean -0.094, deviation from mean 0.277
    10:11:51 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: -0.019 -0.276 -0.308 -0.295 0.345 0.210 -0.002 -0.635 -0.052 0.119, mean -0.091, deviation from mean 0.275
    10:10:23 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: 0.013 -0.257 -0.295 -0.270 0.332 0.229 0.017 -0.616 -0.021 0.144, mean -0.072, deviation from mean 0.272
    10:08:42 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: 0.031 -0.207 -0.226 -0.264 0.357 0.322 0.092 -0.598 -0.014 0.182, mean -0.032, deviation from mean 0.280
    10:06:29 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: 0.031 -0.213 -0.208 -0.245 0.357 0.316 0.073 -0.585 -0.033 0.213, mean -0.029, deviation from mean 0.276
    10:04:59 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: 0.031 -0.307 -0.295 -0.239 0.332 0.291 0.048 -0.598 0.023 0.213, mean -0.050, deviation from mean 0.285
    10:03:30 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: 0.031 -0.238 -0.295 -0.245 0.414 0.297 0.023 -0.604 0.011 0.188, mean -0.042, deviation from mean 0.291
    10:01:38 PMM98 P0:/macros/Bed Measurement 2
    Bed probe heights: 0.019 -0.263 -0.245 -0.245 0.457 0.316 0.048 -0.598 0.011 0.169, mean -0.033, deviation from mean 0.296

    Here is my analysis in Excel for the output (1) and (2) data as image file:

    Here is my analysis in Excel for the output (3) and (4) data as image file:

    I also used mesh bed compensation to generate height map. It is pretty bad. Here is the image:

    Some observations from the excel analysis:

    (i) Running the bed file without trigger height corrections gives less deviations than with trigger
    height corrections
    (ii) Always the first point has more deviation than other points
    (iii) Except first point, the standard deviation of all other points measured in 12 trials are less than 15%

    • I don't know whether to call this as consistent or not

    Currently, I have magball arms and ends from haydn huntly - 360mm length and 60mm arm spacing.
    I read about your PCB effector and it has the same 60 arm spacing. Please put me on the list.

    I am using linear rails and lubricated them. Belts are taut and no slippage of pulleys.
    Endstops are tightened properly. I suspect it might be the scratched PEI surface which is messing
    with the values.

    I have a spare glass plate. I will cut a sheet of matt black paper and place it between glass and
    tooling plate and try bed measurements.

    Please have a look at the files and let me know what you think. I am eager to start printing with my
    delta but issues seem cropping up. Hopefully I solve them and start printing.

    Best Regards,
    Vasan


  • administrators

    The reproducibility when you probe repeatedly without homing is worse than it should be. Normally I would expect most readings to be contained within a variation of about 2 1/16 microsteps, which for your build is 12.5um. You appear to have about 56um range for the first point and 44um for the last.

    You can check the repeatability of probing by setting up macros to move the head up and down by 1 microstep (which is 6.25um on your machine). Lower the head until the LED on the sensor just comes on. Ideally you should be able to be able to turn the LED off and on by raising and lowering the head by 1 microstep at a time. On my delta, it typically takes 2 microsteps (using x16 microstepping, 0.9deg motors and 16t pulleys). You can try this test with a different surface (e.g. paper) on top of the bed if you think the scratches in the PEI may be causing a problem.

    You could also run the tests here https://www.duet3d.com/forum/thread.php?id=1330. These do repeated probing at the same point, with or without travel movement between probing.



  • Hi David,
    Thanks again! I was tired of scratches in PEI. I had a spare glass plate and bought a matt black craft paper. The trigger height was 0.81mm. Just as a try, I used this surface for calibration. The results were consistent and a deviation of less than 10 microns. Now it is clear that the scratched PEI surface is the culprit. If I look at the underside of the glass, the glue which holds the PEI to glass has varying optical nature. This also might have contributed to this error.

    I did run the test with plain glass and matt black paper. Here are the repeatability tests

    (1) Moving the points around in a circle, coming back to the same point for measurement
    2:28:40 PMM98 P0:/macros/Moving around - Repeatability
    Bed probe heights: -0.524 -0.549 -0.543 -0.549 -0.543 -0.543 -0.543 -0.556 -0.556 -0.543 -0.543 -0.549 -0.568 -0.549 -0.556 -0.549 -0.556 -0.574 -0.549 -0.568 -0.568 -0.562 -0.568 -0.574 -0.549, mean -0.553, deviation from mean 0.012
    2:25:12 PMM98 P0:/macros/Moving around - Repeatability
    Bed probe heights: -0.499 -0.531 -0.537 -0.524 -0.524 -0.531 -0.531 -0.537 -0.531 -0.531 -0.531 -0.543 -0.537 -0.537 -0.537 -0.537 -0.543 -0.537 -0.537 -0.537 -0.543 -0.543 -0.543 -0.549 -0.556, mean -0.535, deviation from mean 0.010
    2:21:34 PMM98 P0:/macros/Moving around - Repeatability
    Bed probe heights: -0.531 -0.524 -0.531 -0.556 -0.549 -0.568 -0.543 -0.549 -0.537 -0.537 -0.562 -0.537 -0.543 -0.537 -0.543 -0.562 -0.543 -0.537 -0.531 -0.543 -0.543 -0.537 -0.524 -0.524 -0.531, mean -0.541, deviation from mean 0.012

    (2) Repeatedly probing the same point

    2:18:02 PMM98 P0:/macros/Repeatability - Same Point
    Bed probe heights: -0.518 -0.518 -0.524 -0.524 -0.518 -0.524 -0.524 -0.518 -0.524 -0.524 -0.518 -0.512 -0.518 -0.518 -0.518 -0.518 -0.518 -0.524 -0.524 -0.524 -0.524 -0.524 -0.524 -0.524 -0.524 -0.524 -0.518 -0.518 -0.524 -0.518 -0.524 -0.524 -0.518 -0.524 -0.524 -0.524, mean -0.522, deviation from mean 0.003
    2:10:55 PMM98 P0:/macros/Repeatability - Same Point
    Bed probe heights: -0.512 -0.506 -0.512 -0.512 -0.518 -0.518 -0.512 -0.506 -0.512 -0.518 -0.512 -0.512 -0.512 -0.506 -0.499 -0.506 -0.499 -0.506 -0.506 -0.506 -0.499 -0.512 -0.512 -0.512 -0.512 -0.518 -0.518 -0.518 -0.518 -0.518 -0.518 -0.518 -0.518 -0.518 -0.524 -0.518, mean -0.512, deviation from mean 0.006
    2:09:40 PMM98 P0:/macros/Repeatability - Same Point
    Bed probe heights: -0.537 -0.524 -0.524 -0.531 -0.524 -0.524 -0.524 -0.537 -0.531 -0.531 -0.531 -0.524 -0.531 -0.524 -0.518 -0.518 -0.518 -0.518 -0.518 -0.512 -0.518 -0.518 -0.512 -0.512 -0.512 -0.518 -0.512 -0.518 -0.512 -0.518 -0.512 -0.512 -0.512 -0.512 -0.512 -0.512, mean -0.520, deviation from mean 0.008

    Auto Calibration Results:

    2:46:19 PMM666
    Endstop adjustments X2.19 Y-0.97 Z-1.22, tilt X0.00% Y0.00%
    2:46:15 PMM665
    Diagonal 360.310, delta radius 156.342, homed height 509.946, bed radius 115.0, X 0.039°, Y -0.213°, Z 0.000°
    2:46:05 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.028 after 0.005
    2:44:35 PMM666
    Endstop adjustments X2.23 Y-1.12 Z-1.11, tilt X0.00% Y0.00%
    2:44:31 PMM665
    Diagonal 360.310, delta radius 156.567, homed height 509.912, bed radius 115.0, X -0.080°, Y -0.223°, Z 0.000°
    2:44:17 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.034 after 0.009
    2:42:35 PMM666
    Endstop adjustments X2.17 Y-0.98 Z-1.20, tilt X0.00% Y0.00%
    2:42:31 PMM665
    Diagonal 360.310, delta radius 156.324, homed height 509.950, bed radius 115.0, X 0.040°, Y -0.146°, Z 0.000°
    2:42:20 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.030 after 0.007
    2:40:43 PMM666
    Endstop adjustments X2.08 Y-0.93 Z-1.16, tilt X0.00% Y0.00%
    2:40:39 PMM665
    Diagonal 360.310, delta radius 156.450, homed height 509.929, bed radius 115.0, X 0.129°, Y -0.080°, Z 0.000°
    2:40:31 PMG32
    Calibrated 6 factors using 10 points, deviation before 0.478 after 0.010

    As you can see, they are consistent with very low deviation values. I did mesh bed levelling, here is the height map.

    It seems flat. Now I will print a test circle of single layer to see how good the calibration yes. Will update them as soon as I print it.

    In short, PEI is the culprit. I will try to resurface and reuse the PEI surface if I can with FSR sensors (I have one, so will try it).

    Thank you very much for providing these tests David.

    Best Regards,
    Vasan


  • administrators

    I'm glad you found the problem. Did you paint the back of the PEI black before attaching it to the bed plate?



  • Yes, I did paint it black with stove paint as mentioned in your blog. It looked uniform. Anyways, I cannot back it up with numbers or calibration values.

    I think only after the scratches made by nozzle during initial calibration and test printing, the ir sensor started to give me inconsistent trigger height results.

    I tried a test print of 75mm circle with single layer. The 0.2mm layer came out as 0.22mm layer. I am happy to go past the initial major hurdle of calibration. I will slowly start print other test prints to fine tune the printer.

    I love PEI surface and its adhesion, so I will repair it using sandpaper and CA method by mhackney. I might use FSR on them. I don't think I can use IR on that PEI surface.

    Thanks David for your quick replies and providing various suggestions!

    Best Regards,
    Vasan


  • administrators

    As you are using the magballs from Haydn Huntley, you are in a good position to use the Duet3D PCB effector. It should be available about 4 weeks from now. I was getting good results using the IR sensor on PEI before, but the PCB effector with its built-in nozzle contact sensor is a whole lot better. The rod spacing is actually 55mm rather than the 60mm that you mention, but hopefully it and the carriage adapters will still fit your printer.



  • I am sure it will fit. Please put me on the list. I would like to get my hands on it ASAP.

    //Vasan


 

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