Print quality has degraded

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Re: Print quality has degraded

Postby tmccafferty » Mon Jun 03, 2013 2:41 pm

OK, spent the weekend fiddling with this thing. I disassembled and cleaned the cool end, disassembled and inspected the j-head, and tried endless combinations of temperature and filament size. No improvement. The interesting thing was the consistency of the bad spots on the prints. I was beginning to wonder if it was actually being directed to back off the extrusion rate by the slicer program. From inspecting the parts, it was clear that the extrusion was definitely slowing way down in a repeating pattern. I thought maybe the stepper driver was getting hot and periodically disabling or had some other problem so I swapped it out... no luck.

Finally, I focused on trying to see if there was any variation in the speed of the gear. It wasn't obvious at first, but if you really focused on the gear and the area printing, there was a correlation of the gear orientation (based on the setscrew) and the bad print area. I removed the gear to inspect it but could not visibly see any issue. I had a spare gear so I put it on. It began to print perfectly. It' printed all night with no issue.

I don't know what is wrong with that gear, but it now lives in the dumpster.
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Re: Print quality has degraded

Postby orcinus » Mon Jun 03, 2013 3:51 pm

Very weird.
Eccentricity, maybe?

My herringbone gears are slightly eccentric, to the point where one side of the circle meshes tightly and the other has visible backlash, but i haven't noticed anything as severe in my prints.

Edit: ah, right, can't be eccentricity, because it would've been like that since day one...
Unless it managed to heat up and deform. Is it PLA? Is your extruder stepper experiencing any significant heating?
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Re: Print quality has degraded

Postby tmccafferty » Tue Jun 04, 2013 12:23 am

No heating on gear or upper part of j-head. It has a fan on it.

The gear is metal... Makerbot MK7
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Re: Print quality has degraded

Postby orcinus » Tue Jun 04, 2013 2:02 am

Oh *that* gear.

Ho hum. Perhaps it dulled slightly and started slipping against the filament?
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Re: Print quality has degraded

Postby tmccafferty » Tue Jun 04, 2013 4:08 am

That's about what I'm thinking. It' always the simple stuff although I always start by looking at the more complicated stuff. I should have focused on the repeating pattern sooner.
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Re: Print quality has degraded

Postby flurin » Tue Jun 04, 2013 2:46 pm

tmccafferty wrote:I don't know what is wrong with that gear, but it now lives in the dumpster.


It may be a simple reason. I had similar issues at the beginning with my MakerGear Extruder. The drive gear wasn't tightened strong enough.
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