print quality varies on z axis

[alaris2 1]

I've seen this apparent on several posts including prints of my own - the printer is well set up and works fine, but prints of repeating layers eg. a cylinder, cube or other simple shape where each layer is essentially the same, will have variations in quality on the z axis.

this is seen as differences in color, or thickness, ie. the amount of material extruded.

now we now that variations in filament diameter can cause exactly this problem. layers may extrude too little and string excessively, or worse may be missing entirely such that the next layer prints in thin air.

however in my own case, the filament is fine, variation of <=0.01mm

I can also print many layers (1/2" at a time) at excellent quality and layer adhesion. then all of a sudden I get a bad layer - if it's bad enough, the whole print will fail.

I was thinking of blaming the hobbed bolt, which had a fair amount of plastic on it, as slipping. but a clean later, and no real improvement. I believe the tension of the thumbwheel to be correct (otherwise I wouldn't get as many good layers as I do would I?)

any other suggestions from folks? should I just change for another extruder design entirely? do those with the other extruders get more uniform print quality across layers.. or is it just a different set of problems to face?

[Daid 306]

maybe the Z motor has too little power? or too much and thus the driver is overheating?

[frodeheg 0]

Try to feel on the frame if you can feel any vibration from the fan. I noticed that I got different quality at different layers in the print apparently because the PCB fan below the printer changed speed during the print (however I noticed it in roughness of the surface, not amount of extruded material, so it might not be the same). Try to detatch the PCB+fan from the UM and see if it helps.

[alaris2 1]

strange you should mention roughness - I just had a print failed on me after about the 3rd layer. the machine hadn't been on long enough surely to have z motor overheating problems (I don't think?) although it doesn't rule out too little power. I'll try again with the fan off. thanks!

[alaris2 1]

so I probably shouldn't have done that...

I unplugged the board fan. it made a change to have a quiet print.

on the second layer I noticed a strange X and Y offset, then I noticed the extruder motor was just going click click click.

then I stopped everything.

the extruder motor still went click. it was trying to move one notch and failing, so I powered everything off and pulled the filament out of the hot end.

it sounds like bad news.. is this the noise/symptoms of a hot end plug?

I thought the board fan wasn't strictly necessary except in very hot climates, presumably me having it off caused overheating somewhere. it's only 15C ambient in this room right now tho!

[frodeheg 0]

Sorry if I was unclear. I didn't want you to unplug the fan, just detatch it from the UM, so the vibration didn't transfer to the print.

I hope the board is still ok, it shouldn't be broken in such a short time. (If it is broken I will pay for the repairs since I somehow feel responsible...)

[rock500 0]

I have a similar problem with the Z axis sticking, i have removed the spindle from the steeper, and moved the platform up and down

with the smooth rods in place, and even with oiling the bearings are rough.

I also find i have issues with prints at the 10mm layer, as the platform drops to 10mm when you start prints etc, so its a common height

the printer goes to a lot.

It would be good if somewhere you could very the height (eg between 8-15mm) when the platform drops for a test extrude before a print starts, so

any wear is varied.

[alaris2 1]

oh don't worry frodeheg, I understood your post perfectly. the decision to unplug the fan was mine since it's incredibly noisy anyway and I've been meaning to replace it for ages now. I doubt the board is broken but I'll have a proper look tomorrow - I'm more concerned about understanding those strange click noises from the extruder motor and why they continued even after clicking the 'disconnect' button.

[alaris2 1]

well for the benefit of others, the variation is at least partly due to the steppers needing fine adjustment, as detailed on

http://wiki.meta-concepts.com/display/U ... Adjustment