topic_solved Setting Z Trigger Height
TheIndianDude last edited by TheIndianDude
I'm following the "Test and Calibrate a Z probe" tutorial on the Duet Wiki (https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe) and I'm running into minor inconsistencies with the trigger height. The wiki says that after we bring the nozzle down to touch the build plate or just grab a piece of paper (I'm using a sheet of printer paper), to reset z to 0 (G92 Z0) , move z up 5 to 10 mm (G1 Z5) and run a G30 S-1 to get the trigger height and to repeat these series of steps 4 or 5 times.
I'm trying to get my Z trigger height near the bed 0,0 position (sensor is 5mm in from both X and Y edges) as I want to see the height map relative to the bed origin. After I get the nozzle to the right height, I send G92 Z0, move Z up 5mm, run the G30 S-1 and get a trigger height value. I then move Z down by the trigger height value to make sure it doesn't over travel and that there isn't excess pressure on the paper, re-zero Z, and repeat. The second time, the trigger height is completely different. Here are the values I'm getting:
1st try: Trigger height 0.855mm
2nd try: Trigger height 0.840mm
3rd try: Trigger height 0.837mm
4th try: Trigger height 0.848mm
5th try: Trigger height 0.795mm
6th try: Trigger height 0.822mm
Would these values be considered within margin of error for the IR probe? The website for the probe (https://miscsolutions.wordpress.com/mini-height-sensor-board/) states that the repeatability should be approximately 0.01mm, but I'm getting a variance between 0.003mm and 0.06mm which I think is a massive swing.
Any ideas how I can bring the numbers closer together? Also, what should I use as the trigger value? The last obtained trigger height?
First, I'd suggest using the center of the bed for the Z0 point rather than a corner. Same for homing and setting Z0 before doing a mesh. This is especially important if using any Z axis tilt correction.
Trigger height is going to depend a bit on the surface you're using. Just as a control, try placing a piece of matte paper on the bed and testing the trigger height against that and see if it's more consistent.
Slowing down the dive height can increase consistency a bit, so try that.
Reducing ambient light that could be interfering can help.
Personally I take 10 samples, throw out the highest and lowest and then average them if they are spread out, or take the mode value if one occurs repeatedly.
TheIndianDude last edited by
@Phaedrux Thanks for the tips. I'm using the BuildTak flexplate with a black coating on the sheet steel, so I don't think it's related to transparency/translucency of the bed material, but the surface is rough (to enable better adhesion I suppose), so I will use a piece of matte paper to see if that changes anything.
My standard Z homing is based on the center (updated in homez.g and homeall.g to make sure probe is at bed center). I will move to the bed center and try tuning the trigger height.
My dive speed is set to 10mm/s. I'll try slowing it to half that (been meaning to do that anyway, so now's as good a time as any)
I like the idea of throwing out the outliers and taking an average or modal value.
Thanks for the tips! Will update the thread based on the results.
TheIndianDude last edited by
I followed your advice and I am now getting consistent readings within 0.005mm which is well within the margin of error for the probe. The key was the probing speed and the dive height (Set to 5mm/s and set to 5mm). Once I slowed the probe down and also didn't raise the Z height above 5 mm, the readings were consistent.
Thanks for the advice!