Weird Quality Issue

[tanakas]

Hello,

Please have a look at my print (right click - open in new tab):

Picture Extruder Fault

ExtruderFault.jpg (145.01 KiB) Viewed 14306 times

Initially, for the lower layers, the quality is really good, but then suddenly, at a certain z-height, the print quality is extremely poor, as if it is under-extruding. But then again, the quality is suddently OK again.

This always happens. The height of the poor quality layers is always different, but appears in average more or less every 10-20mm.

Initially, I thought I might have a power/voltage issue, because enabling the heat bed decreases the quality from the beginning. But even with disabled printbed and fans on an external power source, this happens.


Any ideas or suggestions what might go wrong??

PS: PLA

Thanks!

[William]

Hi,I cannot see these pictures about your problem.Could you send it again?

[tanakas]

sorry, fixed it in the OP....

btw, i can exclude:
- filament quality issues
- hot end temperature issues

[William]

Hi,I think there might have some problem in the Z shaft.
You can check whether the shaft of the Z axis can move up and down smoothly.
When necessary,you can add some lubricants(WD 40) to make it freely.
By the way, what is your machine?

[tanakas]

It's a Geeetech I3 pro b.

I am unsure concerning the Z-axis. Yes, I kept them greasy. The "underextruding" would mean that the z rises too quickly during the failed layers. Skipped z steps would rather lead to "overextrusion"-symptoms.


I might have found a possible cause: The PSU-Plug to the GT2560 board was burnt, producing occasionally a loose contact. There might have been a shortage of power for the extrusion motor, which is the one most prone to skipped steps. Anyway, I am now in the procedure of changing the connections, using mosfet's for the heatbed & hotend, and potentially switching to 24V.

I will let you know soon

[rotormansa]

the cables provided with the stepper motors are of very poor quality. I have ordered a few replacements and waiting for them to arrive. In my case it was the extruder cable that failed. In your case the Z - motor cables should not have failed since they don't move, but again the cables are of pretty bad quality. The X-Axis and Extruder cables are always moving so I would expect them to fail, perhaps an upgrade is in order. I would recommend changing out the connectors to soldered wires of at least 20 or 18 gauge stranded copper wire.

[tanakas]

just wanted to give an update (because I dont like those threads with problem descriptions, but finally no solution).

I am 99% sure that the bad PSU plug on the board was the cause for the poor quality. The connection was shaky, and due to vibration, the stepper motors would not work properly, beginning with the one most prone to skip steps: the extruder motor.

I soldered the cables directly to the board and switched to 24V to lower the current. It works great now.

[William]

Glad to hear you solve your problem.

[rotormansa]

Many times skipping issues are related to insufficient drive current on the extruder. Check the voltage on your driver boards. Typically these are set to about 0.5 to 0.6 vvolts. Increasing the voltage to 1.0 to 1.1 volts will eliminate this as a potential contributor to problems with the extruder.