problems in calibration - Z axis keeps getting out of balance
 
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rami.a
(@rami-a)
Active Member
problems in calibration - Z axis keeps getting out of balance

hi guys,
i am sorry for this to be a bit long, but i want to be very articulated with the problems description.

so i finished assembling my mk2 kit. i did all the calibrations as described in the "guide for a new user" video.
everything went well. i printed the calibrating printing "calibration.gcode" and it also went fine.
afterwards i printed two "marvin" figures. and these also came out great.

after turning the printer on, on the following day, i went for z calibration and found out that the z axis is quite off of balance (photo attached).
after calibrating it, i started the x,y,z calibration one more time, and i noticed that although the z axis calibration went perfectly fine, while calibrating the x and y axes, the z axes is going out of balance again, trying to find one of the 9 magnetic points.

i assumed that something is out of tune and made some adjustments. moved the frame about 1 mm so the x and y axes will be super perpendicular. also moved the PINDA sensor a bit higher.

after trying the same process again (z calibration, hotbed leveling, xyz calibration). same thing happened. firs two steps went perfectly fine, then xyz calibration failed (bed calibration point was not found). it happened for the exact same reason. while the printer is calibrating, one of the z axis sides is going a bit lower than the other and it goes out of balance. this time it happened the exact oposite way, meaning the right side of the z axis moved lower than the left one. (on the first calibrating the left side went lower).

i am attaching two photos to illustrate. the first one will be from the first calibration run and the other will be from the last.

im so frustrated! after assembling a fully working printer, suddenly it makes this problems and everything i tried didnt help.

please help me with this one.
thanks!
Rami

Publié : 30/01/2017 3:29 pm
David T.
(@david-t)
Noble Member
Re: problems in calibration

Make sure that one of lead screw covers (on screws at Z motors) is not too close to motor body causing it to get stuck and losing steps.

Publié : 30/01/2017 4:02 pm
rami.a
(@rami-a)
Active Member
Topic starter answered:
Re: problems in calibration

thanks, but they are quite loose.

Publié : 30/01/2017 4:17 pm
Wirlybird
(@wirlybird)
Reputable Member
Re: problems in calibration - Z axis keeps getting out of balance

I would verify all cabling. Does it do this while running or after siting?

Publié : 30/01/2017 8:48 pm
rami.a
(@rami-a)
Active Member
Topic starter answered:
Re: problems in calibration - Z axis keeps getting out of balance

Already checked the cables.
It happens while running.

Publié : 30/01/2017 10:27 pm
JeffJordan
(@jeffjordan)
Membre Moderator
Re: problems in calibration - Z axis keeps getting out of balance

for me it looks as it's likeley that your whole x-axis (from left z-axis rod to right z-axis rod) is a little bit to long, so you'll get a severe tension (pushing outwards) between the z-steppers and the rods. because of this tension your complete x-axis tends to skew in one or the other direction, depending on the movement of the z-steppers.... and of course this tension then is bigger than the torque that the steppers can deal with.

(update:) you can check this out when you remove the trapezoid nuts from the z-spindles (you first need to unscrew their connection from the x-end-motor and the x-end idler part). when your build is perfectly aligned, you should be able to move the whole x-axis assembly up and down (only guided by the linear bearings) very easily... without any tension.


i guess that the x-rods do not sit completely inside the x-end-motor and/or x-end-idler plastic part. or the tension screws are tightened to much.
or the length of the rods was some millimeters to long.

💡
first i would have a look at the tension screws (at the right of the x-end-idler) and loosen them completely (there are other ways to tension the x-belt). then i would press the whole x-axis assembly together to make sure that the rods sit perfectly inside.

dem inscheniör is' nix zu schwör...

Publié : 31/01/2017 9:05 am
rami.a
(@rami-a)
Active Member
Topic starter answered:
Re: problems in calibration - Z axis keeps getting out of balance

UPDATE:

Seems like it was a problem with one of the lead screws protecting the left z engine, as was suggested by david.t2.
When i checked the screws, they were quite loose, but i noticed that when the printer is turned off, it was harder to move the left engine, so i checked the lead screws again and noticed that the left one is being tightened more and more while the engine is moving (right side was all right).
So for now, i have this temporary solution.
Im adding photos to illustrate.
Any suggestions for a better solution?
I guess this small part which caused the problem is damaged. Where can i find a new one to print?

Thank you all for helping!

Publié : 31/01/2017 12:09 pm
David T.
(@david-t)
Noble Member
Re: problems in calibration - Z axis keeps getting out of balance

If you want, try one of my improvements: http://www.thingiverse.com/thing:1916538 😉 You need Tr8x8 version for original Prusa Z lead screws.

Publié : 31/01/2017 12:30 pm
JeffJordan
(@jeffjordan)
Membre Moderator
Re: problems in calibration - Z axis keeps getting out of balance

curious, i've always been asking myself for what these screws are for.

ok, simply to protect the stepper from dust/debris/filament-remainders to get retracted by the spindle...
but when the tiny cover gets retractet itself 🙄

i think davids thingi will do the job quite well :D.

dem inscheniör is' nix zu schwör...

Publié : 31/01/2017 12:40 pm
rami.a
(@rami-a)
Active Member
Topic starter answered:
Re: problems in calibration - Z axis keeps getting out of balance

If you want, try one of my improvements: http://www.thingiverse.com/thing:1916538 😉 You need Tr8x8 version for original Prusa Z lead screws.

sorry, can you explain please what Tr8x8 is? 😯

Publié : 31/01/2017 12:57 pm
Marc
 Marc
(@marc-9)
Estimable Member
Re: problems in calibration - Z axis keeps getting out of balance


sorry, can you explain please what Tr8x8 is? 😯

Hope this helps: https://en.wikipedia.org/wiki/Trapezoidal_thread_forms#Trapezoidal_metric_thread_characteristics

Publié : 31/01/2017 1:29 pm
David T.
(@david-t)
Noble Member
Re: problems in calibration - Z axis keeps getting out of balance

Right. Basically it means that diameter of the screw is 8mm and the nut moves 8mm by every revolution.

Publié : 31/01/2017 3:13 pm
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