Z-wobble or Layer smash?

Not sure if I am experiencing z-wobble or layer squish, or how to get rid of it. It seems that every 10-12 layers (.3mm layer height) I get a ridge as seen in the picture. The ridge is uniform around the whole part.

I do not think this is Z-wobble as this is on a i3 printer design with rubber tubes between the motor shaft and threaded rod. Also the ridges do not match up exactly with my threaded rod (10-32 threaded rod), though they do seem to mate up on every other thread.

Any idea's

Looks like Z Wobble to me, can you print something simpler, preferable in an opaque color, it usually makes it more obvious.
What sort of bearings are you using on your X Ends, what size are the vertical smooth rods?
I had a hell of a time getting rid of the ZWobble on my Mendel Max, I tried 5/8 screws, 1/4-20 screws, 10-32 screws, 1/4-20 acme screws and nuts, I printed isolators (which exposed a different issue), I relocated my motors from the top to the bottom, I used nop heads flexible couplers, I bought spring couplers, I machined couplers on my lathe, in the end I used a different X End design, and brass bushings which seems to have resolved the issue.
Fundamentally if it is ZWobble, it's the screws fighting the smooth bars for control, 10-32 screws ought to be flexible enough that it's not an issue, but that's not necessarily true, you have to make sure everything else is mechanically sound.

Even if it's not traditional ZWobble, and you're losing steps intermittently on Z, it's likely something to do with the screws, or their alignment with the nuts, because as you say it does line up with s multiple of the screw pitch. I know that one of the issues I had with 10-32 screws what that the nuts are very small, and can skew in the nut traps if you're not careful.

8mm smooth rod that is 350mm long. Using 2 lm8uu bearings on each end. Motors are located at the bottom and coupled with soft tube. Ill work on printing something different.

@ Polygonhell

so finally how did you solve the issue... ??? i am facing a simiar problem and cant seem to find a solution..... also what problem do the isolators bring up as you had mentioned???

What I believe finally solved my issue was changing the X-Ends to ones designed for brass bushings, rather than the self aligning igus pillow blocks I originally used.
My best guess is that the "self aligning" part of the bearings was enough to allow moderate Z wobble.
I'm not sure there is a one size fits all solution to ZWobble, you have to figure out what mechanically is causing the issue and resolve it.
Mechanically the smooth rods should be constraining Z motion, but if you use a similar sized screw, it will fight with the smooth rod, especially if it's constrained at both ends.

The isolators have an issue if the paths of the screws and smooth rods (Or just the smooth rods) aren't exactly parallel, you can get into a condition where the X-End floats slightly above the isolator, which leads to inconsistent Z heights.

Edited 1 time(s). Last edit at 11/09/2012 07:45PM by Polygonhell.

i am using 4 mm threaded rods for the z axis and nut isolators .... also i am using linear bearings on the z axis.... but i am still getting banding.... any ideas what is the issue

[imgur.com]

I assume that's ABS, do you get the same thing with PLA?
I get some layer variation with ABS which I think is related to temperature or the plastic itself, but it's not as defined as your image.
You should print a single wall calibration piece aswell, too much plastic can also cause the effect.

Edited 1 time(s). Last edit at 11/10/2012 12:16PM by Polygonhell.

ekaggrat Wrote:
-------------------------------------------------------
> i am using 4 mm threaded rods for the z axis and
> nut isolators .... also i am using linear bearings
> on the z axis.... but i am still getting
> banding.... any ideas what is the issue
>
> [imgur.com]

I have similar results and have tried a lot of things (aligning belts and rods, leadscrews instead of threaded rod etc etc). My next step will be to swap my x-ends to use bushings instead of linear bearings. I have a sneaking suspicion that ebay bearings are good enough for x and y since gravity holds them against one side but Z is a different story.

I have some video of what the banding looks like in my build log

[www.youtube.com]

Any thoughts? Possible threaded rod binding

Alright I have found that the issue seems to be tied to my hotbed.

Hot bed on - Every X height the layers get squashed
Hot bed off - Nice and smooth.

any thoughts how to reduce bed expansion

okay I think I figured it out. Main cause was due to the thermal expansion and contraction of my hot bed, and the fact that the hot bed was secured down too much.

As the hot bed went through the temp swings it would expand and contact in the Z direction causing layers to smash.

Solution
Use PID tuning for the hotbed (Latest Marlin)
Allow hot bed to move or expand in the X and Y direction.