Hm, I measured the distance between the rods at the top, bottom and center. The deviation is less than one tenth milimeter...
I don't need the last 12mm - I just have a bad feeling knowing that there something wrong that I can't figure out.
Thanks for the tipps about the shims.
Is it possible that the plywood of the back panel is warped and is rubbing on the back of the Z stage when it gets that low?
It should be fairly simple to debug the source of this problem - remove the lead screw from the assembly and move the Z-stage up and down by hand. See if the resistance changes. Does the resistance noticeably change when you are turning the lead screw by hand?
I checked it with a sheet of paper between the bed and the back panel. I could slide it freely so I think that's not the problem.
By the way - how do I remove the leadscrew from the Z-stage? I loosened the small screws on the resilient coupling but turning the leadscrew (the M8 threaded rod) does nothing - or at least it doesn't come out.
how do I remove the leadscrew from the Z-stage?
I don't remember it's been so long but once you loosen both screws you should be able to lift the Z stage and the screw should go up with it. If that is accomplished then rotate the z screw until the bed goes all the way down and keep spinning and the screw should slide up through the bed, right?
Hm, I can't lift the z-stage. Maybe the m8 threaded rod sits very tight. I didn't want to force it too much. If everything fails I'll have to remove the smooth rods first and try again.
Thanks for your help.
There are 4 screws in the Z-coupler.
If you remove them you should be able to lift the threaded Z axis without friction.
You will have to screw the axis out of its position, because of the nut that is in the Z-stage.
If this doesn't seem to work, could you post a small video illustrating your situation / efforts?
Thank you,
Ok, I will try that. Here is a little update on this issue. While moving the z-stage the loud grinding noise now happens at random intervalls. So not only 12mm above the grond but also much further above. It is not consistent though and not always reproducible.
Ok, I think I found the problem - but not the solution. The M8 threaded rod is not centered on the resilient coupling. Since the bed forces the threaded rod to one side, it causes friction. I guess that's the reason why I had such a hard time to remove the threaded rod from the resilient coupling. Please take a look at the following image:
http://www.flickr.com/photos/nic0linux/9567180094
I don't know how exactly this happened. Either there is a problem with the laser cut bottom panel or I assembled the frame in such a way that is is warped. However, this is problematic because it leads to z-wobble and exhibits the typical "banding":
http://www.flickr.com/photos/nic0linux/9561039703
But how do I fix it? I can't move the z-motor to the right, nor can I move the z-stage to the left.
Thanks,
Stefan
I would attempt to loosen the back panel of the z-stage and reorient the brass nut so that it has more wiggle.
The screws and rods are fine. It's the stage you need to work with. I think you are going to have to take it partly apart. I spent a long time on the Z stage. I remember after I was done thinking that if I were to have two people working on the UM build at the same time I would have one person start on the Z stage, while the other started at the begining.
I see where this is going. I have to take out the z-stage... Good thing that the smooth rods were hard to insert (even after I have enlarged the holes on the top panel) 
Ok, how should I go about fixing the issue? If I loosen the back panel of the z-stage, the brass nut would start to wiggle back and forth but not in the direction that I need (left and right). I remember that I had a hard time inserting the brass nut into the wooden panel and after that it was extremely tight. Should I take everything appart and rasp away a bit of the small wooden plates that hold the brass nut in place left and right?
Should I take everything appart and rasp away a bit of the small wooden plates that hold the brass nut in place left and right?
I'm not as smart about this kind of thing as most people on this list but, that's what I would do. Sorry you have to take the rods out. You'll have it done in less time than worrying about it.
OR you might get by with having the left side of the bed be more loose. I think it's designed to change widths depending on the width of the rods and lead screw. It might be that just moving the left side of the bed farther out (left) will be all you need to do.
I don't remember doing much about the main "nut". I remember putting in tons of shims on the left arm of the bed to get it to fit on the rods. Spent 2 hours building and inserting shims
@gr5:
Where exactly did you put the shims? Since I need the brass nut to move to the left, I'd put them on the right side. Does this look right to you? thx.
I wonder though why I have to do this. Surely the Ultimaker people would have found this issue with a rev4 build. Maybe I made a mistake somewhere else - but where?
Well your situation may be different but the distance from my right rod to the screw was fine. It was the left rod to the screw.
In your photo. There is a light colored wood board towards the bottom of your picture that connects the left and right arms of the bed.
I had to shim on the left edge of that board with large shims at the top of your image and thinner and thinner shims as you approach the tip of that (beyond the bottom of the picture).
Your situation may be different than mine.
Here is a little update for this issue. I didn't like the solution where I had to change the plywood parts so I re-created the brass nut holder in OpenSCAD and moved it's feet one milimeter to the side. But due to my printer inaccuracy the printed parts did exhibit some warping (why? PLA should be safe - or so I thought and the part sticks all to well to the blue tape) so the entiere back of the z-carriage was skewed.
Original:
My version:
The wobbling issue is a little bit better now, but still very visible :(
Here is a view from the top (it is exaggerated but you can clearly see that the threaded rod isn't centered):
I am at loss here. I don't know what to do next. Fiddle with the brass nut holder or print another batch hoping that it won't warp. In the process of screwing and unscrewing the set screws on the z-coupler (called resilient or resiliert coupling) I broke one bit and now a set screw is stuck forever in the coupler. And even if I unscrew the screws for the z-motor, I can't take the coupler off... Not the ideal conditions for high quality prints I guess.
Looking at your photo from Aug 21.... it looks like the z screw is very high... and is located inside the hole in the top plate of the printer body?
It should sit well below that plate - the top of the z-screw shouldn't be captive at all. If you move the whole z-screw down a bit, so that pretty much all of it's shaft is inside the coupling, then there shouldn't be any reason that you can't center the screw in the coupling by adjusting the grub screws. You will need to make sure that the big nut in the z platform can slide around in its housing a little (as it is designed to) - which might require a little opening out of the holes if it's very tight, or perhaps just some direct pressure to unstick it from whatever position it is in. The brass nut is supposed to just set the z location of the bed, and the two smooth rods that are captive at both ends hold the x-y position.
The z screw is not that high normally, it was just set to demonstrate the offset to the right. It was not inserted into z-coupler at all at that time. I can now insert it all the way into the z-coupler and then it sits well bellow the top plate.
I didn't know that the brass nut should/could slide around a bit left/right. It is very tight and does not move a notch. That's why the z-screw is bent to the side a bit. I guess that's the solution then. I was afraid to change the brass nut holder but thanks to your explanation it is clear now. I will post back soon.
Thanks illuminarti!
I had a similar problem, here is what helped for me:
Status update: HUGE SUCCESS!
Thank you guys. The issue is solved now. I still didn't want to change the parts holding the brass nut, so I printed two new ones. Those are 2mm lower and allow the brass nut to move slightly.
Here is my actual print (left with banding and on the right without):
I still have problems with the stage not moving up smoothly. When I "auto home" via the UltiController, it pauses every second while moving up. But this seems to be something else - not mechanical. Also the motor sometimes still stops and makes loud noises but only when homing or while moving the stage completely up or down.
Your z-homing speed and/or z-acceleration may be causing you to skip steps, causing the odd noises, and stutters.
The ulticontroller axis movement controls are kinda crappy - the code does a really poor job of smoothing the movement. For testing z-speed and acceleration, I'd use something like pronterface, and send gcodes to move the bed up and down, say, 150mm at various speeds, to get a feel for what is workable for your hardware. Listen for smooth movement. You could also stick some bluetape on the inside back wall of the printer, and mark the z-stage position on it. Then run it up and down a fixed distance half-a-dozen times, and make sure you end up back at the same position.
I find that I'm more likely to get skipped z-steps if the x and y axes are also in motion at the same time. Never quite figured that out, but I suspect it's a firmware/timing thing.
You are right, I think it is the dial on the controller and the crappy code. Sometimes I miss menues because the dial moves back and forth althought I just rotated it one notch.
Thanks for the idea with the tape - I will try that.
Hi Nico Linux
I was just looking at your video. I think it's undesirable to allow the nut to spin like that. When it spins it moves with the screw and hence it is not moving the z stage vertically when it should.
Ok, you might be right. But since my threaded rod is deffinitely not centered on the brass nut and the z-coupler, what are my options? I took care to let the brass nut move only horizontally. I hoped that any vertical movement would be constrained by the backpanel of the z-stage. But you are right, if the nut spins it would not move upwards hence screw with the z height (if you catch my drift)
Does the brass nut in your Ultimaker move at all?
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gr5 2,268
The grinding sound is the stepper motor missing steps. It's not serious.
The two vertical rods probably have a different spacing at the bottom of the UM than the spacing for your bed. I fixed this by putting shims on the "left" arm of my bed. I made sure it fit before I finished assembling and did this with the z screw removed.
The design of the bed I believe is supposed to allow this spacing to change as the bed goes up and down but I didn't like that idea and tightened it up good and tight but with shims spacing the arms farther apart.
If you don't need the last 12mm then I wouldn't worry about it. I have not yet needed to use the full 200mm in Z.
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