Print quality has degraded

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Print quality has degraded

Postby tmccafferty » Sun Jun 02, 2013 12:22 am

image.jpg
bad surface 1

My print quality has degraded recently. I can't get a good horizontal finish anymore. I thought it was a filament problem as I had recently switched rolls. However, I switched back to the original and the problem is still there but doesn't show up as bad due to the color I think. I have played with extruder and bed temperatures with no positive affect.

There is an unevenness even on the first layer on the glass. I can't feel any bobbles in any of the axis while moving. Belts are tight and rollers clean. The first layer has varying heights in patches. There seems to be a pattern to it. Also, streaks form perpendicular to the direction of fill on the first layer. They feel like ridges on top and look almost like cracks from the glass side.

It seems like it has to be an extruder issue but it seems to be feeding smooth and I haven't changed any of the Marlin calibrations. Here are a couple of not so good phone photos. Anybody experienced this?
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Re: Print quality has degraded

Postby orcinus » Sun Jun 02, 2013 1:05 am

I get that from time to time.

Possible reasons:
1) temperature too low
2) dirt or other debris on the bed (or just skin oil)
3) melted plastic on the nozzle

Have you tried cleaning and degreasing your bed thoroughly?
That's what cause #1 was in most of my cases.
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Re: Print quality has degraded

Postby tmccafferty » Sun Jun 02, 2013 1:59 am

image.jpg

I think there is more to it than that.... Everything is sticking well. Here is a photo as the part progressed. Notice the voids in the surface.
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Re: Print quality has degraded

Postby blah_59 » Sun Jun 02, 2013 2:40 am

The fact that it is happening at much higher layer heights makes me think you can rule out the bed, it would normalize at those heights even if there was some small debris on the bed. I think that if it were heat, more than likely it wouldn't generate the visible pattern. The fact that there is a visible pattern makes me think that there may be some issue on the cold end drive gear, maybe something there that causes a fraction longer rotation on one side (maybe some plastic in a gear tooth?). This is pure speculation but I think you should investigate on the cold side (maybe even friction on one part of the spool holder?).

Have you changed something in the software chain recently? I was thinking it could be caused by the slicing program as well, maybe...
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Re: Print quality has degraded

Postby tmccafferty » Sun Jun 02, 2013 3:47 am

I agree. I'm kind of wondering if I might be missing some steps on the cold end. Watching the drive, it seems to turn smooth but it's hard to tell. But the higher layers look like there are areas where it's not extruding. When I raise the extruder and extrude 100 mm, I get a nice consistent extrusion.

Not sure how to test it.
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Re: Print quality has degraded

Postby REdington » Sun Jun 02, 2013 5:12 am

It might be the stepper driver is getting hot and skipping steps. When you are free extruding, there is not as much force on the motor to heat the driver and when it is printing the additional force might be heating the driver up.

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Re: Print quality has degraded

Postby orcinus » Sun Jun 02, 2013 11:03 am

Oh, didn't realize it happens on all layers...

Have you tried printing something without infill? Just perimeters, but a lot of them?
To see if there are gaps in the walls.

Granted, the forces are highest when extruding infill against infill, but still, at least it might eliminate some options.

Do the gaps vary with printing speed?
Do they disappear if you lower the speed enough?

If it's an issue with extruding force, lowering the speed should lower the force as well and the gaps should go away.
If they don't, something else is probably causing it.

Have you checked the nozzle for debris or blockages?
I had a similar issue once after switching between two different kinds of PLA. Some tiny blob of old PLA somehow got stuck in the nozzle melting chamber and the new PLA was getting extruded through or around it, causing very uneven flow. The problem went away after a purge at 220ish - 230ish deg C (high enough to ensure both PLAs melt and mix).
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Re: Print quality has degraded

Postby orcinus » Sun Jun 02, 2013 11:15 am

Oh, and one more thing. Moisture.
You can get breaks in extrusion like that from moisture laden filament.

But if the pattern of the gaps is regular, it's not that (also if it never happens w/ perimeters).

A few more ideas:
- trying to extrude too thin (the extrusion getting stretched too much)
- extruding near the threshold of the filament melting temperature (when demand increases, temperature drops, extrusion stops for a moment, leaving a gap or a poorly adhering section, then firmware plays catch-up and heats the nozzle back up to temp and extrusion's fine again until the cycle repeats)
- grease or oil somewhere in your filament feed - i had filament periodically rubbing against my lead screw once, as it was feeding into the extruder, and the results were similar
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Re: Print quality has degraded

Postby flurin » Sun Jun 02, 2013 11:48 am

If you are using slic3r, I would reduce the extrusion multiplier (e.g. from 1 to 0.8) and see what happens.
Further I would install the latest Marlin Version and calibrate the extruder especially the retraction speed.

With Repetier Host you can verify your actual Marlin Version in the log window:

Code: Select all
< 13:33:35: Marlin 1.0.0
< 13:33:35: echo: Last Updated: May 28 2013 07:33:06 | Author: (none, default config)
< 13:33:35: Compiled: May 28 2013
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Re: Print quality has degraded

Postby orcinus » Sun Jun 02, 2013 1:00 pm

Continuous infill shouldn't trigger retracts.
Extrusion multiplier might be illuminating in the same way that reducing speed might - if it helps, it's a pretty sure indicator the pressure / torque is too high.
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