Z-axis not/barely moving, motors buzzing - i3 Pro B Acrylic

[sTuPiD_eLcH]

Hello,

hope you can help. I know this problem has been discussed before, but none of the suggestions worked for me.

I assembled the printer last weekend, but now I have a problem with the Z-axis.
The Z-axis are grinding probably because of the rods slightly being bent and most of the time the motors aren't even moving, just buzzing.

I got the axis only once to go all the way down, but now it's not moving up again.
Sometimes I additionally can push the motors by hand to make them move, but thats not a solution for printing.

I tried:
- lubing the rods
- loosening the screws on the axis nuts and linear bearings
- removing the acrylic plates on top
- adjusting the couplings
- increasing the voltage on the motors to about 1V

If you can provide me with other suggestions, it would help me a lot.
I also found files for new top plates with space for bearings, but the printer can't produce anything in this state.
I was already thinking about getting new (straight) threaded rods, because I think that's the main reason for the problem (as seen in other threads/forums).

The X- and Y-axis are moving fine after I inverted them in the firmware, because they were going in the wrong way to their home.
I haven't tested the extruder yet, I find it more important to get all three axis working first.

Thanks in advance!

[Gareth B]

are your z motors plugged into the correct slots and have you tried reversing the z direction ?? i.e.maybe up command is sending the motors down.

so command the motor to go DOWN and see if it goes up.

Repetier has this setting - try inverting the z direction>>>

also look at this post

viewtopic.php?f=17&t=17037

[bang]

Did you try swapping the driver for Z motors with the one from other motor?

And did you check if the two carriages on Z axis are staying at the same height?

In addition,remove the two threaded rods to check if the motors rotate properly in two directions.If they do,replace the threaded rods...

[sTuPiD_eLcH]

Thanks for the suggestions.

The motors alone are working fine, I think the main reason really is the right threaded rod, which has a visible bend.
I was hoping to compensate this by loosening the screws, but that didn't help much.

Yesterday I adjusted the right side a bit, because I noticed the coupling wasn't centered above the motor.
At first I thought this solved my problem, but after about 3/4 of the way down it started to binding again and eventually stopped with buzzing sounds.

So I guess bang is right and I will need to get at least one new and hopefully straight threaded rod to make this work.

EDIT:

Okay, I take anything back... I FINALLY got it to go up and down without any stuttering, noises or stops!

I disassembled the Z-axis again and kinda wondered, because the rod doesn't seem to be bent this much for the movement it makes while spinning...
So the movement had to come from somewhere else and the lower the nut went on the rod, the bigger the movement got until the rod got stuck and couldn't move anymore.

The reason was not enough/unequal distance between the two sides, which is really hard to notice.
I pulled the two sides a bit apart and suddenly both motors went much smoother.

So theres also kind of a mistake in the building instruction, which shows the silver screw locking rings on the outside, but this doesn't make much sense.
On other models or versions of the printer with black locking rings it's shown to put them inside, which I did with the silver ones now to keep the two Z-axis sides at the right distance.
I also reassembled the couplings once again, which didn't help much, but it's always good to tighten all the screws again.

The only thing I can't use right now is the smooth rod on the right side, which is really a bit bent. So I probably have to widen one of the holes to give the rod a little more space to move.

I hope this might help others struggling with the same problem, because I got really frustrated already with this.


Next step is to test if the extruder is actually working... <_<

[bang]