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MK3.9 - Z axis calibration fails  

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Doddster55
(@doddster55)
Active Member
MK3.9 - Z axis calibration fails

So I upgraded my Mk3S+ to a Mk3.9 and have a problem with the Z axis calibration.
The Z axis moves up to the top, does it's bang/buzz bit, then starts moving down. But it always stops at the same point, 65mm from the Z motor mounts, it never touches the motor mounts.
I have tried it with both 5.1.3 and 5.0 firmware.
When I go into the hardware menu it shows that the printer is a Mk4, but even if I change it to a Mk3.9 it still fails.
Actually it doesn't fail as I don't get an X, just a dash to say the test needs to be run.
Hoping there is somebody who has seen this problem and can help

Thanks,
Graham

Posted : 10/02/2024 7:37 pm
zounds
(@zounds)
Active Member
RE: MK3.9 - Z axis calibration fails

Graham, have you tried checking/adjusting the level of the Z-axis rods? If you have a vertical level (or a bubble-level phone app), make sure the rods are at the same level as the frame in both the Y and X directions. Adjust the Z motor mount screws to change the level.

Posted : 16/02/2024 4:31 pm
Doddster55
(@doddster55)
Active Member
Topic starter answered:
RE:

Zounds, thank you for the suggestion. I have checked the Z axis rods in both direction and they are vertical, no adjustment was needed. Do you know how the initial Z axis calibration works on a MK3.9? While checking the rods I noticed that the hotend would hit the bed long before the X axis carriage hit the Z motor mounts. I only know how it works on the MK3, not sure with the loadcell.

BTW my X and Y axis calibration also fails so I think it's something else like the buddy board, still waiting for Prusa support to respond

This post was modified 1 week ago by Doddster55
Posted : 18/02/2024 10:14 am
JoanTabb
(@joantabb)
Veteran Member Moderator
RE:

on the Mk3.9, 
the Z axis endstop is an integrated Load cell in the Nextruder body, 
so essentially the printer presses the nozzle on the buildplate to set the Z height.

The X axis never gets down to the motor mounts

as you can see in the picture below, 
 
the Mk1 had a physical endstop switch for the Z axis, and required a sleeve on the Z axis rods, to activate the switch But all subsequent printer versions have a gap between the X axis Ends and the motor mounts... 
Mk2 and Mk3 use a Pinda Z axis endstop, 
Mk3.9 and Mk4 use a loadcell for Z axis endstop

regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 18/02/2024 10:57 am
Doddster55
(@doddster55)
Active Member
Topic starter answered:
RE: MK3.9 - Z axis calibration fails

Hi Joan,

Thank you for answering my question, I wasn't sure as my printer hasn't got that far yet 😥 
I guess that because it cannot calibrate X or Y then it has no chance with Z as it cannot center X
Will have to wait for Prusa support to get back with some more suggestions on how to fix this.

Regards,
Graham

Posted : 18/02/2024 11:39 am
JoanTabb
(@joantabb)
Veteran Member Moderator
RE: MK3.9 - Z axis calibration fails

Hi Graham

X axis calibration  failure is often caused by the misplacement of zip ties on the cable support behind the X axis the cable tie nuts must NOT touch the frame
and the X axis must move freely from end to end of the travel range, Belts must be firm but not too tight. 

Y axis must move freely for the extent of it's motion.

There have been some  issues regarding the Y axis bearing location People have found that the Bearing needs to bump into the frame during calibration.. and sometimes the Y axis platform doesn't move far enough... 

the Y platform has two bearings on one side and one on the other, 
On the two bearing side some people move the bearings slightly further apart, effectively making the Y axis, a little Longer
Other people have inserted a piece of hard material between the bearing and the front rod clamp (there are circlip models to print, if you can find them
Both options, seem to work

Other people report the belt tension  can cause issues, loose belts make the axis seem to be longer than expected...

 

Regards Joan

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 18/02/2024 12:21 pm
Doddster55
(@doddster55)
Active Member
Topic starter answered:
RE: MK3.9 - Z axis calibration fails

Hi Joan

Regarding the X axis all ties are correct and do not come into contact with anything. The belt tension was set according to the Prusa App, but I really think it is too tight so I am going to loosen it off and see if that helps.
Y axis: My bed never moves forward, it bangs on the back for a while then the printer reboots with the dreaded 13305 error. I have gone through all the suggestions on the Prusa page for this error with no success.

Regards,
Graham

Posted : 18/02/2024 2:22 pm
JoanTabb
(@joantabb)
Veteran Member Moderator
RE: MK3.9 - Z axis calibration fails

Have you tried putting a screwdriver blade between the Y bearing and the left hand y rod holder?

 

I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK

Posted : 18/02/2024 6:59 pm
Doddster55
(@doddster55)
Active Member
Topic starter answered:
RE: MK3.9 - Z axis calibration fails

Hi Joan,

Lol, no. But I slacked off the bearing holders a bit and also the belt tension and I got a Green check 😊 The strange thing is, if I go with the initial calibration then it fails, but if I go into the menu, set the printer to Mk3.9 and run the manual test then it passes.
With the X axis do you know how far it should travel from left to right? On my display it shows 251mm
Another day so I'm going to work on the x axis, see if I can get anywhere with that

I really do appreciate all your suggestions, thank you 🙂 

Graham

Posted : 19/02/2024 9:13 am
Doddster55
(@doddster55)
Active Member
Topic starter answered:
RE: MK3.9 - Z axis calibration fails - SOLVED

I have just spent over 4 hours with 2 people on LiveChat and can finally print 😀 
It seems that the belt tensions are really important and in my case I ended up moving the X pulley very close to the motor, after this both the X and Y calibration passes.
Thank you for all your suggestions, now it's time to see what this MK3.9 can do 😉 

 

Posted : 20/02/2024 4:49 pm
Dakyleman
(@dakyleman)
Member
RE: MK3.9 - Z axis calibration fails

Great to hear! Was belt tension the source of the y-axis calibration trouble as well?

Posted by: @doddster55

I have just spent over 4 hours with 2 people on LiveChat and can finally print 😀 
It seems that the belt tensions are really important and in my case I ended up moving the X pulley very close to the motor, after this both the X and Y calibration passes.
Thank you for all your suggestions, now it's time to see what this MK3.9 can do 😉 

 

 

Posted : 21/02/2024 1:10 pm
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