Inconsistent Z probe trigger height

cjccjj

Hi, I have an inductive sensor as Z probe with my setup. The print is a corexy setup that the bed has a removable steel sheet with PEI film that is driven up and down by one stepper motor.

I followed the calibration guide and set Z probe trigger height with G31, after some finetuning of the Z trigger height, and G30/G29 probing/mapping, I got perfect first layer test prints.

Then I added G30 to do a single probe and then G29 S1 to load height map to my slicer starting code, I did get perfect first layer for a few prints.

However the other day I printed again, the first layer is not perfect (not too bad but not perfect) , by observing the print I have to reduce the Z probe trigger height a bit to get perfect first layer again (no change to height map).

Bed is heated to the same temperature for all calibration and actual print, and I haven't moved my printer around. Is there any mistake in my process? Where should I look at to get perfect first layer automatically every time?

Thank you!

moth4017

if you try a maro like this:-

M291 P"Probe will be tested 10 times and return mean and standard deviation. Ok or Cancel?" R"WARNING" S3 ; User must click OK or cancel.
G28
M401
G30 P0 X151 Y161 Z-9999
G30 P1 X151 Y161 Z-9999
G30 P2 X151 Y161 Z-9999
G30 P3 X151 Y161 Z-9999
G30 P4 X151 Y161 Z-9999
G30 P5 X151 Y161 Z-9999
G30 P6 X151 Y161 Z-9999
G30 P7 X151 Y161 Z-9999
G30 P8 X151 Y161 Z-9999
G30 P9 X151 Y161 Z-9999 S-1
M402

you can get the average of your inductive probe, inductive probes do change with age and/or heat .

cjccjj

@moth4017
I did a few test on my setup. First 2 groups of test that I home XY or XYZ between tests, it seems that the inductive probe itself is quite accurate, that the deviation is below 0.005. Homing by end-stop doesn't affect the value as expected.

In the 3rd group of test, homing is executed and I manually remove the print surface from bed, bend it a few times and reinstall it back between tests. Now the deviation increased a bit but still at about 0.005 which is good, but for 2 times that the deviation is 0.021, which is 4 times greater. Also the mean value seems shifted about 0.1mm (which should not be a problem). I have no idea why these 2 times have a greater deviation that is big enough to affect first layer quality.

;Home XY between every test
G32 bed probe heights: -0.168 -0.170 -0.173 -0.173 -0.174 -0.174 -0.175 -0.178 -0.178 -0.178, mean -0.174, deviation from mean 0.003
G32 bed probe heights: -0.170 -0.173 -0.175 -0.175 -0.176 -0.178 -0.178 -0.180 -0.180 -0.180, mean -0.176, deviation from mean 0.003
G32 bed probe heights: -0.169 -0.171 -0.174 -0.174 -0.175 -0.176 -0.176 -0.178 -0.178 -0.178, mean -0.175, deviation from mean 0.003
G32 bed probe heights: -0.169 -0.171 -0.174 -0.174 -0.176 -0.178 -0.178 -0.178 -0.178 -0.178, mean -0.175, deviation from mean 0.003

;Home XYZ between every test
G32 bed probe heights: -0.161 -0.163 -0.165 -0.165 -0.165 -0.165 -0.165 -0.166 -0.166 -0.165, mean -0.165, deviation from mean 0.001
G32 bed probe heights: -0.156 -0.159 -0.161 -0.161 -0.163 -0.163 -0.163 -0.166 -0.166 -0.166, mean -0.162, deviation from mean 0.003
G32 bed probe heights: -0.164 -0.168 -0.168 -0.169 -0.169 -0.170 -0.170 -0.170 -0.173 -0.174, mean -0.169, deviation from mean 0.003
G32 bed probe heights: -0.169 -0.173 -0.174 -0.175 -0.175 -0.176 -0.178 -0.176 -0.175 -0.178, mean -0.175, deviation from mean 0.002

;Home XYZ and manually remove and put back steel sheet between every test
G32 bed probe heights: -0.164 -0.168 -0.169 -0.170 -0.170 -0.174 -0.173 -0.174 -0.173 -0.174, mean -0.171, deviation from mean 0.003
G32 bed probe heights: -0.175 -0.178 -0.178 -0.180 -0.180 -0.183 -0.183 -0.183 -0.183 -0.185, mean -0.181, deviation from mean 0.003
G32 bed probe heights: -0.308 -0.304 -0.298 -0.283 -0.274 -0.270 -0.265 -0.261 -0.253 -0.240, mean -0.275, deviation from mean 0.021
G32 bed probe heights: -0.136 -0.134 -0.130 -0.128 -0.126 -0.125 -0.123 -0.123 -0.121 -0.120, mean -0.127, deviation from mean 0.005
G32 bed probe heights: -0.285 -0.271 -0.261 -0.256 -0.253 -0.249 -0.241 -0.230 -0.221 -0.216, mean -0.248, deviation from mean 0.021
G32 bed probe heights: -0.136 -0.133 -0.131 -0.129 -0.126 -0.126 -0.125 -0.125 -0.123 -0.120, mean -0.127, deviation from mean 0.005

moth4017

@cjccjj
ok instead of G29 S1 just do a G29 and see if the 1st layer is better

cjccjj

@moth4017
It didn't show a difference for my recent prints, both have quite nice first layer. However those are small prints at the center of the bed. My printer is a small one the bed is 230x150, and seems pretty flat from height map, I had been watching but never found any movement of Z when it prints first layer with height map enabled.
Actually for most prints the first layer is good enough, the difference is fine vs perfect only for large print. I guess the inconsistent comes from the whole system. I see videos of the Bambulab printer does pretty long calibration for every print, and it vibrates a lot when calibrating. Maybe that vibration not only helps input shaping but also help the whole mechanical system to settle down to the same state.
Thank you for the input! And btw, the spamming system of this forum stops me from posting or replying or editing twice in the same day, I have to wait a day or two to reply....