What would cause zits on curved walls only?

As you probably know, in S3D, you can see where all the retractions are in the Print Preview to see if they occur there.

This is exactly what I am seeing in my prints (piercet’s photo).

It’s not retractions. And it doesn’t appear to be related to the beginning and ends of loops. Because if that was the case, it would also occur on straight walls (assuming you used random start points as I usually do).

Also I have not been able to effect this with slicer settings in any way.

I don’t believe it is material issues such as moisture, because again, it would occur everywhere in a print, not just curved walls.

How about posting a small curved wall model so the interested folks can test and tweak?

EDIT: How about the attached, for those who want to test…
Calib-Curved wall.stl (292 KB)

I just purchased an E3D V6 to test it out.

I am not getting any zits on curved walls with this new extruder. The main difference between the Taz Hex and the E3D is the cooling above the hot end.

So that leads me to think the cooling above the hot end is the cause of the zits on curved walls. Makes sense.

So you could go with a stronger cooling fan on the hex and perhaps that would fix the issue, if you don’t want to replace the extruder.

My only gripe with the E3D is they limit you to 290-295 because the thermistor they use will fail above that. Kind of silly. I suppose you could swap theirs out with the NTC 100k and get rid of that limitation.

AN E3D fixed it??? What the heck?
I suppose there is a reduction in flow in a curve, so it almost has to either be cooling, or inner surface polish of the bore. I have a 40mm fan on my Hexagon already so it should be getting plenty of air, and the thermal camera seems to think the fins are staying cool, so I’m wondering if it is the bore polish then. I guess it’s time to buy an E3D V6.

Did you have to make any firmware changes, or is it just plug and play?

Interesting… I printed the test print I posted, and it looked fine…

I’m also interested in any firmware tweaks to support the E3D V6 thermister. I’ve adapted the holder plate, but haven’t actually used the toolhead.

Well you need to print a different layer fan duct because the extruder sits lower than the hex, but you can get that on thingverse. Also I had to design a “washer” to sit between the top of the E3D housing and the base of the printed extruder housing because otherwise it is loose on the aluminum bracket. Or you can buy a different aluminum bracket but the washer is easy and cheap. I can post the stl if you want it. You can also print a plastic bracket to replace the aluminum. Frankly you can get away with that with the E3D because it’s not even warm to the touch on the cold side of the extruder. I am very impressed with their extruder cooling design. Much better than the hex. Although the temp is limited to 290-295 on the E3D as I mentioned. But that is easily addressed with a different thermistor (a few dollars).

As far as firmware goes I just had to rerun the optimization for the hot end. They said to change the thermistor setting but my .h file was already set to what I should change it to. There are instructions on the upgrade on matterhackers website and there is a wiki for assembling the extruder itself (it’s easy and much cheaper to buy the extruder kit). Do a google for E3D v6 Taz 5 installation. Just beware Matterhackers links to the wrong E3D v6 version. It should be 3mm direct drive and 24v. I’m sure you know that though. They don’t though lol.

ps I completed my design for 12mm X rod upgrade and installed it today. FANTASTIC! I have less than .1mm sag in X now. A HUGE improvement. I am just running my first print with a .1mm layer height and the first layer was perfection. I am so happy. I will post the stl’s on thingverse and post a thread here when I get the chance.

Nice! Glad the 12mm rods are working well for you!

I ended up getting the e3dv6 kit bundle that also comes with the volcano head. I think I’ll have a bunch of extruder mount and body rework ahead of me, but it shouldn’t take too long. That might be combined with the other bondtech core extruder project since I finally got all the parts in for that too.

Here’s some pics of my new extruder, 12mm bar upgrade and a view of some early layers of a print. And Piercet’s antiwobble upgrade too.

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?

Makes you kind of wonder what LulzBot R&D is doing in their spare time?

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.

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?

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.

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.