What would be the cause of z artifacts that appear as z height increases?
the vagueness…
What type of printer?
Does your Z have rods or pulleys?
If you have rods for your Z height, do they wobble and does it matter if they do?
Is it a delta style or cartesian style printer?
People that can tell you your answer will need to know those things and many more details before settling on an answer.
Good luck figuring it all out.
Are you talking about bumps or about something in the g-code?
Sorry about that, it’s a makerfarm prusa i3v, z rods wobble a little when moving but prints look perfect, its only when it gets above 80mm that the layers begin to have some artifacts. The artifacts look like the hotend is wobbly or something, there’s no pattern but the layers don’t line up exactly.
Ok. It looks like the Z rods are 370mm long. You say it starts at 80mm. I imagine the Z rod wobbles more in the middle of it. There is a loose hold allowance on the Z rods to allow for the idea that your Z rods may get warped. It could be that it is not allowing for enough wobble or in other words that your Z rods might be way too warped.
It could also be that by the time the extruder gets to 80mm off the print bed that the plastic holding it in place has gotten hot and too soft to hold it still. There is a fan on the hot-end’s cooling fins to try to avoid having heat creep up the hotend to the filament. I do not know if that helps keeping the plastic from melting or not. Now I have to ask if you are printing in ABS when the printer was made for PLA. Some people print stuff they shouldn’t in PLA (like the extruder mount) too. To test if your hotend’s bracket is melting, I suggest a long screw driver or something else that won’t melt. You sure as heck do not want a hotend burn. Trust me on that.
I’m certain that the extruder remains cool, I have an E3D and if the fins get warm then I would get PLA jams, and all my extruder parts are ABS.The mounting plate I’m using is a bit thin though, so I’m making a new one that’s more snug to prevent the extruder from wobbling.
@Mark_Estefanos It might be that your threaded Z rod is wobbling more than can be negated then. Perhaps keep an eye on your smooth Z rod and the plastic bits on your X and see if more than just the threaded Z rod is wobbling. That is as good as I can figure. I do not have a cartesion bot myself, but I have read many posts about people with issues like this.
Hmmm…I guess there is one other possibility else than the Z wobble. What if the two motors are not turning 100% the same amount due to skipped steps or friction? I have heard of that sort of stuff happening too.
We’ll have a better idea of your problem if you can post a picture of the print artifacts in question. 
My guess is that as your Z nuts move up the rods, and the angle of the rods going through them changes, the nuts are rocking in their sockets and not staying level. This could cause a slight vertical wobble either due to the contact point between the nut and the X end changing, or the nut applying torque that causes the whole X axis to wobble. In either case, this would cause the nozzle to rise at an uneven rate as the axis goes up.
All good theories and all a huge pain to test Right now I’m getting slight layer lines even at lower z heights when I didn’t before, so its also possible that the longer I print the more something comes loose. I’ll put up photos in the morning.
As Whosa stated, I ad the same issue with my makerfarm i3. When the Z would jump up, the nuts would slide sideways in the wood piece and it would cause a small blob on the exterior of the part… I epoxied the nuts into the wood holder and it helped.
The makerfarm kit is a GREAT value, but it has TONS of room for improvement. If possible and if I was going to keep mine I would invest in the z-slot upgrade that they are now offering. That would solve alot of the issues this machine has including, I suspect, the z artifact issue you are seeing.
Actually, I have the V slot version, I upgraded my standard i3 and it was a great upgrade. I’ve been looking more into it, and I’m starting to think it’s just z artifacts that appeared over time. Heres a print from today with contrast to show the ribs. http://imgur.com/LBsbkD0 Looks a bit odd as every few ribs is a bit more pronounced. @Whosa_whatsis @Arthur_Fedderson @NathanielStenzel
hmm… to me that almost looks like a stuttering bearing on the x or y axis… of course with the v-slot im not sure. Do you have your belts flipped on the idler?
There is an android app called SpectralView. You could touch the phone to various parts of a printer and watch for inconsistent frequency patterns to locate problems. I just figured I would mention it since I have used the trick myself and the list of things that might be wrong seem to keep growing under this post. Good luck.
@Arthur_Fedderson I don’t have the belt flipped, is that standard practice?
@NathanielStenzel Thanks for the tip, but I unfortunately don’t have an android.
https://itunes.apple.com/us/app/spectrumview/id472662922?mt=8 if you have an iphone
It can help with some z artifacts. If I remember right, the teeth riding over the idler changes tension as it skips between teeth. This might be something to look at, though to be honest, I would think it might be more evident on the whole surface rather than in just a few areas.
I’ll definitely look into it more. Thanks Bill! Nathaniel, I’ll give that a shot as well. Thanks again for all the help
That would be an X/Y artifact, not a Z artifact.