Printing Problem where the Z-axis moves

Bern
Posts: 2
Joined: Sun Nov 29, 2015 9:29 am

Re: Printing Problem where the Z-axis moves

Post by Bern » Wed Jan 13, 2016 5:31 am

I have the same problem with Z axis it wobble. One of the threaded rods if not booth are bended and it cause the efect.
Take a look to my video at
https://youtu.be/EU-F90GWxno
How you proceed when the threaded roods has this defect for a printed that has been bought only some weeks ago?
It has a kind or garantee and you send replacement rods?

Mark
Posts: 1553
Joined: Thu Aug 06, 2015 9:19 am

Re: Printing Problem where the Z-axis moves

Post by Mark » Wed Jan 13, 2016 5:24 pm

seems yours is not that bad, you can try to print. And if you want to repalce it, you need to contact the sales.

Bern
Posts: 2
Joined: Sun Nov 29, 2015 9:29 am

Re: Printing Problem where the Z-axis moves

Post by Bern » Wed Jan 13, 2016 7:29 pm

Thanks a lot for your quick reply.

I have to admit that the video is not really good, the perspective of the video and the size of it makes the effect sometimes soft.
But if you take a look at the end of the video, when the Z axis is going to finish the homing process, you will appreciate how the motors of the extruders move from left to right respect to the threaded rod on the background. More and less like it does for our friend "rmrodriguez" in https://www.youtube.com/watch?v=aBcGf69i9RI.

My conclusion regarding to that is that if the defect could be visible to the naked eye that means that the movement is about near or more that 1mm, so that, the printer will lose any kind of precision of 0.4mm, 0,2mm or whatever.

So that, just in case a bad assembling is influencing in that wobbling, in addition to the bending, and I could improve the defect, I will appreciate if you have any procedure, information or something to assemble and calibrate perfectly z axis.

Thanks a lot Marc

Mark
Posts: 1553
Joined: Thu Aug 06, 2015 9:19 am

Re: Printing Problem where the Z-axis moves

Post by Mark » Fri Jan 15, 2016 3:48 pm

get two straight rods.. :D

robmar
Posts: 6
Joined: Sat May 21, 2016 5:58 am

Re: Printing Problem where the Z-axis moves

Post by robmar » Sat May 21, 2016 7:28 am

Hello Bern,
My reply comes probably a little bit late, and hopefully you've fixed the problem by now.
But I'm posting it anyway, since it could be useful for others facing the same issue.
After building my Geeeech I3 PRO B I've encountered the wobble problem right from my very first prints. Even with a properly configured and tuned setup, my prints were constantly showing a wavy surface along the Z axis, and since the wave was not randomly placed but appeared with fixed pitch, evidently a lot larger than the set layer thickness, I was puzzled at first and did not understand the source of the problem.
Then, browsing the forums, I heard about the Z axis wobble issue, and suddenly everything became clear. Evidently, if for some reason the Z axis screw is bent or if for some reason it is not revolving exactly around its axis, the lateral movement of the screw causes the whole X axis assembly to shift slightly with a period that matches the pitch of the Z screw. This accounts for the constant pitch of the wavy artifact, exactly that of the screw, and also its wavy look reflects the "sinusoidal" law of the problem: a bent screw brings, for every complete revolution, a left deflection sideways (X-), then a backward deflection (Y-), then a right deflection sideways (X+), then forwards (Y+) and so on, revolution after revolution. That's why the artifacts usually do affect both X and Y directions of printed object, so all around it and not just on one side.
Moreover the problem could change with the Z working height, due to a localized non linear bending of the screw, and also from the interaction of the different phase of the force applied by the two Z screws, in case both are bent not the same way.
Thus the possible fixes are:
1) Straighten or replace the Z screws
2) Fit in a decoupling fixture (you can find many examples googling "geeetech i3 Z axis wobble") that separates the horizontal coupling from the vertical one between the Z screw and the X axis bridge)
3) Check for any misalignment between the Z screws and the couplers fitted on stepper motors. In my machine, for instance, I found that the Z screws and the motor shafts are not vertically straigt each other. (It's easy to check by simply decoupling the Z screw, lift it a bit and see if it tends to "naturally" fall on the coupler exact center axis r else there's a displacement) This will cause a wobbling effect even if the screw is perfectrl straight, due to the small but nonetheless harmful angle of insertion of the screw into the coupler. Because of this, you will notice that the coupler doesn't turn straight but bending around its axis, and the effect on the X axis displacement is more evident the lower the position of the Z axis that, judging from your video,is exactly your case.
In this case the solution is to rework the Z stepper holder plate (or to make a new one with the correct measures)
I managed it by making the motor plate holes oval (including the big hole for the motor flange) thus allowing for fine positioning of the Z motors exactly underneath the screw.
I strongly suggest to check starting from point 3), since the defect I encountered came evidently from a wrong design of the motor holder plates, it is very likely that there will be a whole production lot out there bearing this very same defect.
Regards,
Roberto

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