z-offset increasing 3mm on every subsequent calibration
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@vj said in z-offset increasing 3mm on every subsequent calibration:
EDIT: I may have a BLTouch Smart v2.0, which has the range at 3mm+/- 0.3, but I'm out of range (my 3.84 is when it is deployed, but when it is not I for sure have less than 2.7mm). That my indeed explain the inconsistent readouts! Ok, so going to rewire and reattach the bltouch: If I put it at 3mm, I should be fine regardless of whether I have a v2 or a v3 (but I'm 99% sure I have a v2). THANKS!!!! Not sure if this is the cause, but it seems possible.
Your words are very familiar to me. This is exactly the pain I went through with the BLTouch. There's a set of slightly different instructions and no simple way to tell exactly which version you have in your hand. Incredibly frustrating!
Once you get it set up properly, it's very repeatable and reliable though. Not as repeatable or accurate as my Precision Piezo, but that wouldn't have been a good option for a cartesian printer.
I just checked my other printer and the Z trigger height (or offset) for my BLTouch is 1.3mm. 3.84 doesn't sound right to me. Like I said, make sure that the base of the sensor (not the pin) is 8mm from the bottom of the nozzle.
Good luck and we'll hear from you in a couple of weeks!
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Ok, finally getting back to this...
I've got it ... I think... If you do a mesh compensation, and afterwards determine the Z-offset with the mesh compensation in effect, it will affect the determination of the Z-offset... As I was doing the homing in the front left corner, but the Z-offset calibration in the center, it added the mesh offset calibration which I did before the print (but which was not used in the print) when the z-offset is calculated again afterwards. As I was using the mesh calculation to check how level everything is, it enabled it, giving me an increase equal to the amount it is compensating with the mesh (and that was a magnitude off due to other wrong settings)... Does this make sense?
I currently started repeating Z-offset calibration without mesh compensation in between, and it seems correct...
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Thanks!
Perhaps a note on https://duet3d.dozuki.com/Wiki/Test_and_calibrate_the_Z_probe should be added that mesh calibration should be off, or that at least you should test at a point where the calibration has 0 effect...?
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@VJ Done.
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Hi,
Perhaps the firmware could handle this automatically by ignoring any active mesh calibration when setting Z=0 using a Z probe?
Frederick
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I'm not sure that that is so straightforward... Also, it is nice that the firmware just does what the command tells it to do, without performing additional steps behind the user's back. Sure you have to know more what you do, but at least it allows you to do what you want.
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@VJ said in z-offset increasing 3mm on every subsequent calibration:
I'm not sure that that is so straightforward... Also, it is nice that the firmware just does what the command tells it to do, without performing additional steps behind the user's back. Sure you have to know more what you do, but at least it allows you to do what you want.
But when would you ever want to set Z=0 with mesh compensation active since it doesn't accomplish anything useful?
As it is you need to remember/know to use G92 S2 before G30 for it to work right.
And as we see that need can cause problems.
Frederick
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Or you can just include a M561 in your homez.g and homeall.g files before your G30 ever gets called. This wipes out anything a G29 may have set.
Personally, I like the fact the machine doesn't make assumptions in the firmware. Assuming to ignore the G29 could be bad for certain applications but good for others. Making the user use the available Gcode commands to wipe or remember settings is a positive and makes RepRapFirmware very flexible for multiple platforms outside 3D printers.
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Can you provide an example of when executing a G30 when mesh compensation is active makes sense?
As pointed out the result is not meaningful.
Frederick
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A laser engraver would be one example where you might use G29 to measure your bed surface, and then perform a G30 to re-zero your Z axis against an object your going to engrave to set the proper z height for the correct focus length. You want the laser to move in a consistent plane, but will want a different Z position for laser focus against an object.
The same can be said for a 3D engraver or a small milling machines.
