Problems With Z wobble?

Hey guys. I've been having some trouble with my lines going across my prints lately. I have a Prusa Mendel Iteration 2 with a makergear hot end and I print with PLA. I know for a fact that my Z rods aren't 100% straight because my motor mounts don't completely line up with my X ends. I was wondering what solutions there are for this problem. I've tried unbolting my motors and installing Z rod contraints to the bottom of my Z threaded rods. I don't like unbolting my motors though because they move up and down, therefore affecting my layer heights. I'm currently printing out another pair of Z rod contraints for the top of my threaded rods as well to see if those make any difference..

Here are a few pictures of my prints that clearly show the Z wobble:

Z wobble on Prints

Any help would be greatly appreciated!

Edited 2 time(s). Last edit at 04/29/2012 12:36PM by cordawg92.

You need to have the Z Rod Constraints at both the bottom AND the top. Otherwise, it won't do much good. When you add the Z Rod contraints with the 608 bearings, they are always a bit loose, so wrap the threaded rod with about 8 cm of thing Kapton or electrical tape where the 608 bearings will contact the threaded rod. This cinches up more of the slack and reduces even more of the wobble.

Also, change your Z motor couplings to Nophead's Z couplers. at [www.thingiverse.com] . If you don't have thing rubber tubing available for the Z motors, just wrap them with regular electrical tape (kind of loosely) till you build up about 1.5 - 2 mm around the motor shaft.

When you tighten the new couplers up, rotate the shaft a bit, and look at it to make sure that it appears in perfect alignment.

Do these, and your prints should look amazing. On Monday, I will post some pics of the before and after of my first Prusa Mendel. My before pics looked like yours, my after pics show no banding.

I'm using nophead's Z couplers already with rubber tubing. Is there a special way that i'm supposed to be aligning my couplings, or do i just tighten them on? I'm almost done printing out my second set of rod constraints, so hopefully they make a difference

Edited 1 time(s). Last edit at 04/29/2012 01:28PM by cordawg92.

cordawg92 Wrote:
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> I'm using nophead's Z couplers already with rubber
> tubing. Is there a special way that i'm supposed
> to be aligning my couplings, or do i just tighten
> them on? I'm almost done printing out my second
> set of rod constraints, so hopefully they make a
> difference

You may have noticed already but just in case, in the couplings the cylindrical recess is wider at one end than the other,
obviously the wider being for the threaded rod. Apart from that I just tightened mine on.

Mike

Okay, nothing changed V_V

new prints

I only use 6mm (1/4") lead screws as they will bend instead of moving the entire axis around. Thus allowing the smooth rods to do their jobs and not be fighting with the 8mm threaded rods to be the guide for z axis.

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That's an interesting take on it, however I'm not really interested in switching my M8 rods to m6. I would rather try working with whatever hardware I currently have (if it's possible)

You will need really really straight rods then as they are as strong as the smooth rods and will always move the axis around if they have any wobble.

Did you do as Prusa suggests and try NOT tightening the z motor screws and allow them to wobble and absorb the issue?

P.s. A large portion of the best printing machines use trapezoidal lead screws (acme threaded) or small diameter (e-maker huxley = 5mm diameter)

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I tried unbolting my motors, but when i printed with them unbolted they moved around too much. They moved the x carriage up and down as they moved

I have seen people using zap straps to hold the motor down while still allowing them to wobble. Maybe try that.

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I've been fighting this (and stalking every related forum post) for months now.

I've tried (with varying degrees of success):
-nophead's printed couplers with vinyl tubing
-spiral cut aluminum couplers
-1/4" acme leadscrews
-lubricating the threaded rod/leadscrews
-adjusting pololu driver current
-using a decoupled nut holder ( [www.thingiverse.com] )
-leaving the z-steppers unbolted, strapping them down with zip ties, bolting them down
-using constraints at the bottom of the threaded rods
-recalibrating extruder steps/mm

I've only once achieved a print without any horizontal artifacts (on the right in the attached photo). At this point I'm not even sure what I did, because I can't recreate it. Most of my prints look like the one on the left. The effect is deliberately exaggerated by the angle of the lighting.

I solved this same issue on my cupcake with [www.thingiverse.com] and I'm thinking of designing some x-ends that contain similar sprung nut holders.

I had some Z wobble myself. I used this solution: [www.thingiverse.com]
Z wobble gone.

tsb4k Wrote:
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> I've tried (with varying degrees of success):\
> -1/4" acme leadscrews

If this did not work I would think you have other issues like:

Only using 1/2 stepping and having a layer height that does not play well with your steps per mm on z

Or having the z motors disabled when not in use which can cause lost steps.

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Sublime Wrote:

> Or having the z motors disabled when not in use
> which can cause lost steps.

I just checked this to reassure myself that I wasn't silly enough to overlook it, and guess what..
Will re-compile and try again!

Let me know if this is the case. Does it help if I tell you that I'm using Sprinter instead of Marlin? Could that be an issue?

You need to unbolt the motors (not using the built in 3mm threaded holes). I placed a gasket material (a 1/4" thick semi-compressible foam like weatherstripping) in between the Z motors and the Z motor bracket, and then used Kapton tape to tape down the Z motors fairly tight. The foam gasket material decoupled it by allowing the motor to move in the X and Y directions to further decouple the motor. The Kapton tape has a bit of springyness to it so I wrapped it about 3 times. I wrapped the Kapton tape (which was only 6mm wide) and taped each Z motor twice.

Your issue isn't a Sprinter vs Marlin issue, although Marlin will give you smoother parts in the X & Y directions.

I did have one machine that I used Nopheads couplers on, and when I tightened down one of the couplers, it was slightly off on the alignment. So it is possible to misalign them, but much harder to than if you used the traditional single piece coupler that comes with most RepRap Prusa Kits.

have you tried to lower the flow rate on the perimeter. i may be wrong, but i think the perimeter width is wide enough not to be flattened entirely by your nozzle. a lower flow rate will determine that, and possibly lead to better prints. this would also explain the banding and the bulging you see with the prints. best of luck. maybe lower flow rate on perimeter by 10%

Sorry for hijacking your thread again Cordawg!
Not having any luck so far. Getting kind of discouraged since I've rebuilt or replaced almost everything.

-Keeping the z steppers enabled had little to no effect
-Made sure the x & y belts are tensioned and not rubbing against any guides
-Lowered acceleration in the firmware

Not much left to try except fine tuning the extruder.

The effect I'm trying to eliminate is pretty subtle but looks bad when lit obliquely.

It could be that your threaded rods don't have a linear pitch. I have seen somebody post that the thread can be at an angle so you get a sine wave added to the motion. That would explain why nothing you do improves it.

I use stainless steel rods and my couplers and get no wobble at all. I have also checked my Prusa z axis with a digital scale and it was as accurate as the scale, i.e. 0.01mm.

The theory of the coupler is that the can flex angularly so it doesn't matter if the rod is a little bent. The coupler flexes to accommodate it and so it doesn't try to bend the smooth rods. As long as there is no play in the linear bearings it cannot wobble. Any other form of constraint makes no sense.

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[www.hydraraptor.blogspot.com]

The causes and remedies of Z-Wobble (and layer height variability), in a nut shell

0. Bent Rods. Don't use bent rods.

1. Variability in the thread pitch. This is known to be a problem that can look like z-wobble. Most threaded rod that you get at the hardware store is going to show some variability in thread spacing. If it is severe, you will notice it in the layers. One good way to check a rod before purchase is to use the long nuts, commonly used to join two lengths of rod. By running the long nut through the entire length of the rod, you will be able to detect any rough spots, indicating a problem with the thread. It could be the pitch spacing, or it could be something else. Either way, you don't want that rod. Also, check the rod for straightness by rolling it on the edges of the shopping cart basket. Don't buy any rod that shows even the slightest hints of wobble. You should expect about 1 out of 6 rods to be good.

2. Moderate to severe run-out in the concentricity of the rod, and a stiff (no flex) coupling.
A coupling that simply serves to link the motor shaft to the threaded rod can only work if the linkage is perfectly concentric. If your coupling is printed, this will never be the case. Strapping down the motors or the rod will only make things worse. If you have access to a lathe, you can try and true the shaft alignments, but a better solution would be to get better couplings.

If you go with flex couplings, you will need to isolate (tie down) the motor AND both end of the threaded rod. This means you need thrust bearings (a 608 and two nut will do in a pinch, as long as the rod is a tight fit). Flex couplings are meant to carry no load, because they tend to be springs, so if your motors are on top (Prusa) you need the thrust bearing to carry the load of the X-axis.

If the motors are on the bottom (printrbot, mendel), there is a bit of support if the rod is resting on the motor shaft, but this can cause damage to the motors' bearings over time. With thrust bearings in place, and secured motors, the flex coupling is an ideal interface for rotary motion, transferring none of the lateral stuff.

Of course, all of this is only important if you are trying to get really awesome prints. My Prusa has flex couplings with no thrust support, and as long as the filament rolls freely, the layers come out pretty good all the same.

YMMV

-Wildseyed-

cordawg92 Wrote:
-------------------------------------------------------
> I tried unbolting my motors, but when i printed
> with them unbolted they moved around too much.
> They moved the x carriage up and down as they
> moved

That should not happen, are your Z end plastic parts aligned, not warped and are the X rods level?
The best low-cost method is to use M6 rods as Sublime also mentions, they don't fight the M8 smooth rods for alignment, they give me perfect prints on my MendelMax.
Rod constraints don't usually fix the problem completely, and can make the problem worse if your rods are bent and your motors can't move a little.

You could try fitting zip-ties instead of bolts, that really helps, or just one M3 screw to hold the motor, that can help, but zip-ties do work well.

If not, replace with new Stainless steel threaded rod sections, and try to get them as straight as possible.

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[richrap.blogspot.com]

u might want to take a look at a 'slide coupling' we used for compensating wobbly z rods.
[www.youtube.com]

[github.com]

in section 7 of the assembly manual, you can see how the 'slide coupling' works.

i am sure you can modify the x-ends for use with a dual z-motor prusa.

I did a similar thing.

I know this is very late, but I fixed it. I finally got rid of the Z wobble: [imgur.com] (The left cube is with the wobble) , [i.imgur.com].

I replaced my M8 threaded rods with 1/4" Acme lead screws. I also replaced my motor couplings with a piece of rubbing tubing and some zip ties. For anyone still suffering from Z wobble, I highly recommend you switch our your M8 rods for something thinner. I chose 1/4" acme because the nuts are the same size as M8 nuts meaning I didn't have to reprint my X ends.

One more pic of the new couplings and rods: [imgur.com]

Edited 1 time(s). Last edit at 02/23/2013 10:15PM by cordawg92.

I was struggling with z wobble on my new mendelmax. My solution with standard 8mm threaded shafts and nuts was to not use the spring and nut on top. I had read that in some old post on this forum. May not be the best solution as the x carriage is now using gravity to hold it in place. But it did allow me to get printing again and there is zero wobble. Nice clean prints.
My long term fix is to look into 6mm threaded shaft or the acme shafts.

I did that as well. I removed the spring and nut on top. I don't know what the difference would be if I put them back now, because I did all of the changes in one shot. However I hear that it is a fix for a lot of people.

try this [prusaprinters.org] helped me a ton

@bigsean:
You noticed that the thread is hundred years old?
-Olaf