What would cause zits on curved walls only?

A forum dedicated to the stock LulzBot TAZ 3D Printer
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Re: What would cause zits on curved walls only?

Post by wmgeorge64 » Thu Apr 21, 2016 7:30 am

Makes you kind of wonder what LulzBot R&D is doing in their spare time?
ULS Laser . Retired master Electrician in Iowa USA Lots of Hobbies

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Re: What would cause zits on curved walls only?

Post by billyd » Thu Apr 21, 2016 11:35 am

piercet wrote:I finally got around to finishing my own E3Dv6 modification, but with a twist. I decided to use a stock Taz heater core and Thermistor with it to help determine "is it something with the hexagon barrel" or "is it something with the hexagon electrics". With preliminary testing I can now safely say that the E3DV6 does indeed cure the curved wall blobs, and that the stock thermistor and heater core for the hexagon are not the issue. For my test I used the exact same motor, exact same hobbed bolt, and identical, but not the exact same thermistor and heater cores, on the same modified Taz. I also used the same nozzle for each one. I just now finished dialing it in.

Early conclusions:
1. The E3DV6 barrel does work better in rounded curved sections than the Hexagon barrel (it eliminates the issues I was seeng without introducing new ones), and in most other cases does not seem to be any different than the hexagon in performace.
2. Adding additional cooling or removing cooling from the hexagon does not seem to have an effect on the issue. This leads me to believe it is NOT the fin profile of the hexagon that is the issue.
3. The hexagon hotend electrical components are not a concern.

So, with that said, there is something that needs to be improved on the hexagon for ultimate print quality. I suspect it has to do with the length of the overall barrel section and the difference in bore taper. It may also be the inner polish of the bore, or the type of aluminum they are using. I'll continue to experement and see if I can get the hexagon to perform like the E3D v6, but I'm not sure I even have the equipment to make the necessary modifications. I dunno, we'll see?

Wow so it's not the cooling. Truly strange.

I have been very happy with the E3D v6 it has been trouble free through many hours of prints.

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Re: What would cause zits on curved walls only?

Post by Sebastian » Thu Apr 21, 2016 12:53 pm

Very good test / comparison!
Maybe you find something inside the extrusion channel of your Hexagon hotend? As others don't have this problem it might be a manufacturing issue?

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Re: What would cause zits on curved walls only?

Post by kcchen_00 » Thu Apr 21, 2016 3:33 pm

FWIW, the regular/original Hexagon barrel is taller than the AO variant. Its almost on par with the E3D V6 barrel. Would be worth a comparison. Maybe the heat dissipation isn't as efficient with the shorter barrel.

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Re: What would cause zits on curved walls only?

Post by piercet » Fri Apr 22, 2016 4:44 pm

After being puzzled by this for a couple of days, I've come up with a theory about what is happening, but not why, and definitly not covering why the Hexagon does it and the E3DV6 doesn't

I believe that what we are seeing here is more plastic than should be oozing out the end of the nozzle in corners because the X axis goes from very rapid motion to almost a dead stop for a couple of seconds. I think that abrupt stop allows the molten plastic "sometimes" to extrude out with more force than normal. Why it only does it some layers remains a mystery. It might have something to do with the layer gap left after one of those excessive ooze layers. On subsequent layers the excess plastic ends up filling in the gap left by the ooze event instead of continuing to ooze. The other theory is that on those corner events, the air seal caused by the solid plastic and transition state semi molten plastic "plunger" is forced over sideways enough to break the air seal and that allows the plastic to run further than normal. The issue doesn't seem to be affected by different plastic sizes though (I have tried 3.2mm fillament down to 2.5mm fillament without effect.)

Here is the best cutaway comparison of an E3Dv6 and a Hexagon that I can find. The hexagon pictured is not complete, it doesn't show the limits of the heat break tube, and it's probably a 1.75mm non AO variant. but you get the general idea.

Once the plastic enters the nozzle, they are effectivly identical since both hotends share the same nozzle at the moment. The heat break, heater cartridge section, and bore are all somewhat different, so I suspect whatever the cause of the blobbyzit phenomenon is somewhere in there.

My next test is going to be fitting an E3DV6 heater block to the hexagon, and the hexagon heater block to an E3Dv6 and see if the issue switches extruder bodies. After that, swapping the heat break tube if I can get them out.

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