[Solved] "Dead" first layer calibration  

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jehrman
(@jehrman)
Active Member

I couldn't find an answer to this question (sorry if I missed it) - but is there a way to adjust the first layer calibration value without being in "live", i.e. in offline or non-printing mode? I just dug an impressive trench in my brand new smooth bed, because I wasn't fast enough to raise the nozzle from the setting I was using for my textured bed. I understand the hardware settings for different sheets - that's not my question. Just wondering if there's a way to set the first layer offset from e.g. -1.25 to 0, or -0.5, or some other safe distance *before* the extruder is moving across the bed, short of doing a full-blown xyz calibration?

Thanks, Jim

Posted : 25/11/2019 6:10 pm
jehrman
(@jehrman)
Active Member

Ha! Never mind. I should have tried live adjusting Z while the printer was idle. Looks like that works even then. Sorry to bother everybody.

 

Posted : 25/11/2019 6:13 pm
rmm200
(@rmm200)
Noble Member

I am sorry - I can not visualize how you would want that to work.

The printer has to lay down a first layer. The extruder has to move to do that.

And it has to be at the correct Z height to print that first layer.

Posted : 25/11/2019 6:52 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: @jehrman

I couldn't find an answer to this question (sorry if I missed it) - but is there a way to adjust the first layer calibration value without being in "live", i.e. in offline or non-printing mode?

If I'm understanding you, you want a way to set a "safe" value before starting a Live-Z calibration. I stumbled across a gcode setting that would allow this, but I must not have saved the link. In the meantime, with firmware v3.8.1 you can reset profiles for print surfaces which include zeroing the Live-Z offset. Of course, the PINDA needs to be properly installed to ensure that 0 doesn't drive the nozzle into the bed. If the PINDA is properly installed, the firmware endstop limits downwards movement to 0.15mm. Is this a printer that has been used before or a new one? I'd verify the PINDA height before trying too much more.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 25/11/2019 7:59 pm
jehrman
(@jehrman)
Active Member

@bobstro

In settings, there is a Live Adjust Z entry that (apparently) lets me adjust this up or down, even when the printer is idle. I'm assuming that this adjustment would take effect once a print is started? I haven't tested it yet, but maybe somebody with Prusa can verify. For example, if my current first layer calibration is -1.25, and I adjust it through settings to -1.00, *then* start a print (or first layer calibration), the extruder will be positioned at this new height? I certainly hope it does, because then I can retract the extruder to a "safe" height, and not dig a trench in a new printing plate when I calibrate the first layer for the first time.

Posted : 26/11/2019 12:12 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: @jehrman

In settings, there is a Live Adjust Z entry that (apparently) lets me adjust this up or down, even when the printer is idle.

Yes, but with a couple of caveats:

  1. If you are using the multi-sheet profiles in the latest firmware releases, that adjustment is only for the currently selected sheet profile. It is automatically saved to the profile when you make adjustments. If you select another sheet profile then return to the original, the original should reflect the last changes you made via the menu. You can reset a profile in the menu to be safe.
  2. You need to complete the on-board Live-Z adjustment at least once per profile. The Live-Z offset should be set to 0 for any new profiles, but there's a chance there's an old setting (e.g. if you didn't do a factory reset when updating firmware). 

I'm assuming that this adjustment would take effect once a print is started?

Live-Z adjust the "zero" position in the firmware. The idea is that you want the printer to move to the correct height for the 1st layer when sent to the 0 position. Live-Z allows you to make minor up and down adjustments to the zero position. As such, it's a printer setting and independent of gcode.

I haven't tested it yet, but maybe somebody with Prusa can verify. For example, if my current first layer calibration is -1.25, and I adjust it through settings to -1.00, *then* start a print (or first layer calibration), the extruder will be positioned at this new height? I certainly hope it does, because then I can retract the extruder to a "safe" height, and not dig a trench in a new printing plate when I calibrate the first layer for the first time.

You should not be able to drive the nozzle into the sheet using normal move commands if your PINDA is properly set. The PINDA should be adjusted mechanically to a point where it triggers above the bed. With no further adjustment, the nozzle will be moved to the point that the PINDA activates (light goes out) and stop some distance above the sheet. When properly adjusted, this point will be approximate 0.2mm (IIRC). Live-Z allows you to adjust it to go a bit lower than the trigger point, but should still be above the bed.

If you go into a terminal program connected to the printer, you may see "software endstop activated" messages if you attempt to drive the nozzle into the bed. In reality, the printer will not allow the nozzle to be moved below 0.15mm. If your nozzle can be driven into the bed, you need to adjust the mechanical height of the PINDA probe so it triggers sooner.

Note that mesh bed leveling does further tweaks to the layer height based on measured bed evenness to attempt to maintain your Live-Z setting consistently across the entire print surface. These adjustments are done during the mesh bed leveling step prior to every print.

Hope this makes sense!

 

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 26/11/2019 3:46 pm
jehrman
(@jehrman)
Active Member

@bobstro

Thanks, I'll check all this out. My remaining confusion is that, if indeed the PINDA senses the bed surface as you describe, why should any difference in printing sheets matter? Wouldn't the PINDA only allow the nozzle to be lowered to the optimal distance (including any first layer calibration adjustment) regardless of varying thickness in the bed? Or does the PINDA behave differently depending on the type of printing plate (smooth vs. textured)? When I switched beds I assumed what you are describing, that if the setting for my textured plate (-1.25) gave me a good looking/behaving first layer and was nowhere close to hitting the bed, then switching to the smooth plate at a -1.25 setting would in the worst case give me a non-optimal first layer. Instead the nozzle definitely plowed into the bed - not seriously but it did leave quite a mark. To be clear, I didn't select another sheet profile - I was using the same one that worked for the textured plate, and made no adjustments other than swapping plates.

I did check my PINDA height again (using the cable-tie method as in the assembly instructions) and it looks to be correct. When resting on top of the cable tie, the nozzle is slightly but definitely above the print bed, and certainly not touching.

But all is well here - no new accidents and I have what I need to swap plates without mishaps.

Posted : 26/11/2019 5:32 pm
Dave Avery
(@dave-avery)
Honorable Member

the PINDA detects the flex steel sheet, so different sheets have different thicknesses of PEI coatings on top of the steel that "live" Z needs to be adjusted for

Posted : 02/12/2019 10:54 pm
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