Z Calibration - Nozzle comes down on heat bed hard during calibration setup  

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

No, it should not be. Make sure that your extruder is correctly mounted and that the PINDA is max. 1 mm higher than the tip of the nozzle.
Compare with the pictures on this page ...

https://manual.prusa3d.com/Guide/9.+Preflight+check/514?lang=en

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Thank you for the quick response and advice. I checked both my hot end / extruder installation and my pinda probe position and they are as illustrated and instructed in the manual. I wonder what else could be the issue? I am tempted to re assembled the whole hot end and extruder assembly.

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

For the start: you have done the full calibration (XYZ), including the the Z calibration as mentioned in the description?

Is the probe reacting on metal (led goes on/out), if not he probe is sensing nothing and you should determine why the probe isn't working properly
If yes: place the probe 1-2 mm lower (down) what happens then?

Frans

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Hi Frans. Thanks for your reply and help. Yes, I have correctly followed calibration instructions. I can print sucessfully with my Mk3, and everything seems to be working coorectly while I am printing. However, I find when I print the parts on the right of the bed stick better then those positioned to the left and the bottom surface "lines" are spaced further apart to those on the right. I was trying to improve my z calibration. However, when I run the calibration routine the nozzle/hot end comes down onto the bed as described above.

I have decided to rebuild the complete hotend and extruder and check all the wiring connections.

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Hi again all,

After rebuilding my Mk3 and taking extra care to be sure everything was done correctly I am still having the same issue. One thing I have noticed is the pinda probe comes down slightly off centre of the printed circle on the heatbed during the calibration wizard. However, the probe itself seems to function ok when a metallic surface is placed under it. And besides the hotend pressing down hard when the calibration wizard is run I can print successful. Are there any other users who have encountered this? Any other thoughts. I have tried adjusting the pinda height many times without success. Thanks.

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Evan:

I presume you have been printing previously ok and this happened when you tried to do a z calibration when this issue popped up. What prompted the z calibration that you did? did you change the assembly somehow (physically?) or move the printer? Edit: I did not read the comment about you adjusting your bed level above before posting, but my suggestion below remains after I read that...

One thing to consider is did you zero out the live z value and or any live z offsets that were set before doing the z calibration? Support previously instructed me to do a mesh bed level, Z Calibration and then live z when I made an adjustment/moved the printer... Also to zero out the live z before hand. Presuming there was nothing mechanical that was adjusted to cause the crashing,

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

On my Mk3 - it "sounds" like the nozzle it hitting/hammering the bed; but it isn't actually touching. Just the mechanicals rattling when the motors stop.

If during the calibration the nozzle isn't dragging the sheet of paper on the bare heat bed, the nozzle shouldn't be hitting the steel sheet, either.

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

jbinfl - Yes, my MK3 prints well enough. Bed adhesion is a bit average on certain parts of the bed and why I have run the wizard quite a few times. I have also moved my printer around within the house a number of times, and thought it best to run after doing so. No hardware mods.

I didn't know that about the live Z. So no, I did not zero that out. Maybe that is the cause. I figure it's user error on my behalf somewhere as the printer works perfectly well besides the obvious issue. I have ordered the new MK3S upgrade and once assembled I'll give it another go with zeroed out z value. Thanks for sharing that info.

tim.m30 - This happens during the initial calibration wizard, steel sheet removed. But the nozzle does indeed push down onto the heatbed. So much that the Y rods/rails bend in the process. I'm tempted to video it as I probably don't explain it very well. Thanks.

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Did you do the manual setup where you set the PINDA height and ensure the nozzle does NOT hit the fiberglass bed?

But there are enough tales of cal constants being wrong that you may want to do a factory reset with the complete clear option. That's worked for others who have had weird Z-Axis offset issues (10mm too high was common).

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Thanks tim.m30. That might be a good option also (the factory reset). For the moment I'm printing, and wanting to do the new extruder parts and Y axis parts.

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Evan:

I agree with Tim on the factory reset and re calibrate. No, the nozzle should not slam into the heatbed, that is not normal and something is not right. It sounds like the pinda height is not correct, see the picture in step 3 of the link below. If the pinda is raised the nozzle goes lower so for the nozzle to slam into the bed the pinda would be too high.

https://manual.prusa3d.com/Guide/9.+Preflight+check/514?lang=en #

Now, a factory reset will erase everything and you will have to recalibrate, so it is a process. Do not know if you built the kit or received assembled, but is sounds like assembled... I would read the stuff on the link above and watch the video before doing anything and then attempt it. You will have to redo the calibrations and live z to get it back to what you have now, but hopefully the nozzle will not crash into the heatbed. As always the live chat on the prusa page when logged in is helpful as well.

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Thanks again jbinfl. My Mk3 is a kit, built by me late last year. Originally I set the Pinda height based on the supplied zip ties, and that's the height it has been for most of the time. Last week I spoke to support via chat and they said to use the tip of the zip tie rather then the middle part. This did not work either, the nozzle still contacted the heat bed, but less forcefully I thought.

I'm going to give it all another go. Zero out live z, factory reset all data and try again with the pinda height set as per the manual.

Re: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Evan:

Sounds like a plan. I wanted to be conservative in my post above in case you did not assemble the kit so you would understand it was an involved processs. I am glad you assembled the kit so you have experience in that part of it. I probably could have worded it better though...

I hope you get it figured out and get back to printing!

RE: Z Calibration - Nozzle comes down on heat bed hard during calibration setup

Hello,
I know this thread ist really old but so is my printer (mk2s).
I have exactly the same issue after changing the hotend of the printer. I had a big filament blob and accidently rip of the cable from the thermistor. Hence the hotend was old and the heatblock heavily scratched, I decided to change it completely. I had another Hotend from the MMU1 Kit that I have not yet installed. Before I had no issues with z-calibration or bed leveling.
I already checked the PINDA height, did a factory reset and tried to run XYZ-, Z- and bedleveling-calibration.
The result is the same for all of them. For the first calibration point everything is ok. But from the 2nd on the nozzle hits the bed slightly. From the 4th on the bed is pushed down really hard. During the XYZ calibration the paper moved on the first spot. 
I also checked the PINDA itself. On all spots it stops when I hold a metal putty knife under the probe. 

Has anyone another idea what could cause this behaviour?