Undiagnosed z-artifacts

Its been a long struggle, countless hours (over 100), and frustration trying to get rid of all of my z artifacts. I have upgraded to 8mm acme leadscrews which are perfectly smooth and straight, z axis decouplers, strengthened frame, tightened belts and screws...ect. Attached is a photo of the artifacts that my "z resonance test" from MAKE show (but also seen on every print). This was printed at .25 mm layer height (with 4 decimal places of proper rounding based on reprap layer height calculator). I also used a cooling fan to the layers were not soft and melty. Seen in the photo, there are large bulges seen fairly repetitive, but do not match anything about my TR8*8 leadscrews, which rules out banding. To furthermore isolate the problem, I printed at around 15 mm/s, so there were absoluetly no vibrations or resonance from the mechanical aspect of the printer. I am just about out of ideas. However, I was told that if a hobbed bolt is not perfectly cut and perfectly round, then it can cause artifacts like this, and mine has a very slight odd shape to it, as seen in the other attached image, however, math I did proves that the layer heights and bulges just dont add up :/. If anybody has gone through anything similar or has ANY ideas at all what the problem may be, I would be eternally grateful. Also, if this may be any hint, if I do,say .1mm layer height, the artifacts are much, much smaller.

you definitely want your hobbed bolt to be better than that.

If you have restraining bearing on your Z axis threaded rods, remove them.

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Dirty Steve
you definitely want your hobbed bolt to be better than that.

If you have restraining bearing on your Z axis threaded rods, remove them.

If i decoupled the acne leadscrews from the x carriage should I still not contain them? They are not attached to the carrage at all and don't change the quality whether constrained or unconstrained. But I will definately try a different hobbed bolt.

I'm referring to a bearing on the end of your lead screws, opposite end from your Z motors (see photo), if your setup has them, not the attachment to your X carriage.

I make my own hobbed bolts, I had one that was 'out of round' like yours, correcting that was my final Z artifact fix on my printer. It causes different amounts of material flow.

Edited 2 time(s). Last edit at 01/26/2015 02:37PM by Dirty Steve.

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Dirty Steve
I'm referring to a 608 bearing on the end of your lead screws, opposite end from your Z motors, if your setup has them, not the attachment to your X carriage. I make my own hobbed bolts, I had one that was 'out of round' like yours, correcting that was my final Z artifact fix on my printer. It causes different amounts of material flow.

I understand. What I have read is that constraining the z axis screws at the top will cause the x carriage to move around if the screw is bent (z wobble), but if the x carriage is completely decoupled from the x carriage then theoretically it won't move around at all from a bend in the Leadscrew right?


I think it would be useful to add that I use an aluminum flexible coupling on the motor shafts

Edited 1 time(s). Last edit at 01/26/2015 03:39PM by TheReprapExperience.

I'm not understanding how you would decouple the x carriage from the lead screws.

It's possible by "anti-wobble" mechanics, for example this one:
http://www.thingiverse.com/thing:141479
or that one:
http://www.thingiverse.com/thing:33053

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Ano
It's possible by "anti-wobble" mechanics, for example this one:
http://www.thingiverse.com/thing:141479
or that one:
http://www.thingiverse.com/thing:33053

Maybe I should be more clear... This is why I don't think it is wobble becuase i purchased high quality anti backlash nuts which are far superior to those diy nut traps, and yes, by uncouple, it guides along the smooth rod like that and pushes up the x carriage. The x carriage is in no way attached to the z nuts, meaning I can pull it up and it moves down with gravity

Edited 1 time(s). Last edit at 01/26/2015 04:20PM by TheReprapExperience.

I was just answering Steve, because I have no idea, what it could be. Perhaps your bolt is causing some effect that add up with others or something.
If you didn't look up this wiki-page, perhaphs you can finde a cause (or multiple ones) for your problem: http://www.reprap.org/,
but other than that, I'm sorry to say, but I don't know.

You are not using a bowden setup, are you?
And your filament is without problems, for example air bubbles or diameter changing (like 1.75mm being between 1.5 and 2.0)

Edited 3 time(s). Last edit at 01/26/2015 05:11PM by Ano.

It could just be your hobbed bolt. Double check that your hot end assembly doesn't have any wobble in it's mount.

Is the Artifacts.jpg print you posted single wall?

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Dirty Steve
It could just be your hobbed bolt. Double check that your hot end assembly doesn't have any wobble in it's mount.

Is the Artifacts.jpg print you posted single wall?

It is a cube with equal sized sides all the way up. For my hotend, I wrapped Ptfe tape around it so it is stiff in the jhead mount, and to furthermore expel and movement/vibration errors i printed painfully slow, about 10-15 mm/s and this took a good 2 hours to print, rather than a normal 30 mins, and the quality was the same on both.

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Ano
I was just answering Steve, because I have no idea, what it could be. Perhaps your bolt is causing some effect that add up with others or something.
If you didn't look up this wiki-page, perhaphs you can finde a cause (or multiple ones) for your problem: http://www.reprap.org/,
but other than that, I'm sorry to say, but I don't know.

You are not using a bowden setup, are you?
And your filament is without problems, for example air bubbles or diameter changing (like 1.75mm being between 1.5 and 2.0)

No I am using the wade extruder in the original i3 design. In terms of filament I am using high quality makerbot filament, which, for an unresonable 50$ for .9kg, prints the exact same as 25$ deltamaker filament which has been opened for half a year. The makerbot filament is very consistent though, and no airbubbles or anything.

I purchased a new hobbed bolt which is of high quality but the problem is still present

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TheReprapExperience
Maybe I should be more clear... This is why I don't think it is wobble becuase i purchased high quality anti backlash nuts which are far superior to those diy nut traps, and yes, by uncouple, it guides along the smooth rod like that and pushes up the x carriage. The x carriage is in no way attached to the z nuts, meaning I can pull it up and it moves down with gravity

The Z axis doesn't need expensive antibacklash nuts because the weight of the X axis - i.e. gravity- always keeps the nuts loaded.

Check the bearings on the Z axis- make sure they don't allow any wobble, and make sure the guide rails are solidly mounted.

Edited 1 time(s). Last edit at 02/06/2015 09:28AM by the_digital_dentist.

What kind of motor couplers do you have on your Z axis lead screws? Top or bottom mounted motors? Pic?

Edited 1 time(s). Last edit at 02/06/2015 05:09PM by Dirty Steve.

I'm using flexible machined aluminum couplings for 8mm screws on bottom mounted motors. No mis-alignment that I can't tell in the couplers

Is the spring part of the couplers collapsed from the weight of the X carriage? I have top mounted motors on my machine, but I recall a tread somewhere about placing a 4mm ball bearing inside the couplers, to space the lead screw off on the end of the motor shaft, and to expand the flex part of the couplers.

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Dirty Steve
Is the spring part of the couplers collapsed from the weight of the X carriage? I have top mounted motors on my machine, but I recall a tread somewhere about placing a 4mm ball bearing inside the couplers, to space the lead screw off on the end of the motor shaft, and to expand the flex part of the couplers.

Essentially I have my leadscrews seated ony motor shafts so that the coupling does not compress with the weight of the x carriage.

I'd do some searching on that, I think the lead screws setting on the shafts reduces the flex machined into the couplers. The ball bearing acts as a pivot. I think you want some compression, just not completely compressed. I'm out of suggestions as to what could be causing it.

Edited 2 time(s). Last edit at 02/07/2015 08:27AM by Dirty Steve.

Bed temperature variation can cause Z-artifacts. Are you using bang-bang or PID control? Does the bed temperature remain reasonably constant during printing?

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the_digital_dentist
Bed temperature variation can cause Z-artifacts. Are you using bang-bang or PID control? Does the bed temperature remain reasonably constant during printing?

That's what I thought, but I printed the towers with no heating to rule that out. It does remain consistent though so it's probably using default PID's

Could it be an issue with the way the spool is mounted? Sometimes the tension from the filament might be pulling up the extruder, and then when that tension is released from the filament spool turning a little, the extruder moves back down.

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Rayton
Could it be an issue with the way the spool is mounted? Sometimes the tension from the filament might be pulling up the extruder, and then when that tension is released from the filament spool turning a little, the extruder moves back down.

That's what I thought at first, but I printed another tower while holding the filament keeping plenty of slack and there was no difference in the wall smoothness

I just tested 3d printed no flex couplers and if there is any improvement, it is very subtle and not the main source of the problem. The x gantry has some flex so I may reprint the i3 rework where the bearings are tie wrapped which are stronger and maybe other x carriage ends where the rods are screw tightened to prevent more flex.