What are these dark spots?

[TheRealJoost 5]

While printing Taulman t-glase clear I am starting to see this dark spots and stripes (see picture). Can't quite figure out what is going on. I am printing with 255C/60C - am I perhaps too hot and burning the material as it prints? If so I would have expected a more continuous stream of carbonized material.

Thoughts anyone?

[ultiarjan 1,223]

I have the same with collorfabb XT, it's burned, I've never been able to solve it.... If you go to cold on XT the layer adhesion is poor...

[TheRealJoost 5]

Yeah, that is what I thought. I've done a few initial prints that did not have this though that was with lower temps, layer adhesion seemed ok but i did not closely inspect. What surprises me is that I get this little poop-lets instead of a sort of continuous stream of dark material. It is as if some part circulates in the block/nozzle a bit, gets burned and then comes out.

I am no expert in plastics but wonder if the nozzle's internal structure is not optimal. Oh well, I will need to experiment a bit more to see if prints can be made with good adhesion and no burning.

[peggyb 171]

it is because these materials are more sticky (PET,nylon) than PLA. Loose extruded fragments are dragged externally along the nozzle and at some point get dropped somewhere. The only way to avoid it is to sit by the printer with tweezers and clean the nozzle tip when this happens or optimize your gcode to avoid these loose fragments (speed, temp., retraction, combing, etc)

[neotko 1,417]

Sometimes it's brown goo that stays between the ptfe/hotend or ptfe/i2k. I had to do quite a lot of atomics to remove it completely because I had some of that on some hightemp prints. Also a perfectly clean nozzle helps.

[TheRealJoost 5]

@peggyb: yes I have seen these little brown sticky things hanging around. The print this time took over 30 hours. Although hanging around the printer with tweezers to catch them little boogers might be therapeutic, 30 hrs might be a bit too therapeutic. How would I go about optimizing the gcode? I take it you mean to go in and edit directly or set up a different regime from within Cura?

@neotko: I've done a few atomics but also put a heat gun at 260C on it to let things drip out and scrap a bit with a tooth pick. I wasn't too impressed with the atomic method to clean the nozzle, heat gun worked much better as verified with a microscope/boroscope.

Guess I will have to print at lower temps and hope the adhesion is sufficient.

[peggyb 171]

the comment with the tweezers was a bit cynical.... meaning: undoable for long prints. I have done 40 hour prints with PET and there will be some of these spots. It is hard to predict where they will be, best is to know your materials before starting a bigger print and take them for granted. And when you take a look at the progress of the print once in a while (unless you're away the whole time) clean the outside of the nozzle when necessary. This is quite challenging with tweezers, the head is fast at movements, so pick the right time to do this, during infill is good, when you can predict how it moves..

[TheRealJoost 5]

 

@peggyb: What was the gcode optimization you were referring to?

[peggyb 171]

know your materials: speed, temp., retraction, combing, infill etc. for each material/color, even another color may act different. Check the layer view to see what the path of the nozzle is.

For large prints this maybe a tedious thing to do, but it helps to watch the printer and notice where it picks up material.

[gr5 2,265]

You can always use black nylon.

[krys 206]

Hi folks,

If it helps, I print XT and T-Glass at 240 and it seem decent enough in strength, and no burnt bits. For example, I have printed replacement dowel pegs for my futon in T-Glase @ 240 and they are plenty strong enough to support 2-3 people weight over at least a year. (Use more shells and infill for strength.)

That said, I have had burnt bits and other black spots, and doing several atomic pulls to really clean things out solved the issue.

Also, if my previous prints are in black ABS, then I get dark spots. Same solution though, atomic pulls.

I forget my nylon (Taulman Bridge) temperature, but same issue, and same solution.

Anyway, hope this helps.

[Kyle_fer 2]

Old topic, I know, but I am getting this problem too, is anyone who has this problem using an Oiler?

I have a theory, when I cleaned my nozzels last, I noticed a lot of burnt bits within the Nozzle, which I think is cooked oil residue, like how when PLA ran through an oiler gets stuck on the outisde of the nozzle, it leaves behind a brown stain when it is cleaned off. Those stains are constantly being built up on the inside.

My theory is that perhaps this is bits of cooked oil buildup from printing at such high temps.  I use Canola Oil and it has worked very well for me and solved many many many issues, I plan to use a higher temp grade oil in the future.

Edited March 21, 2017 by Guest

[krys 206]

Hi there,

I have used sewing machine oil when printing Ninjaflex, but I never correlated that with my dark spots. So, maybe, but I am not sure.

Switching from a dark colour to a light one, or from ABS to PLA, or printing too hot and burning the filament would all seem to be more likely causes, I would think.

That said, maybe Canola or other cooking oils would produce different results.

Still, I do not think you need oil unless you are printing a flexible material.

Anyway, hope this helps. Good luck!

[geert_2 558]

In my experience, if the spots are dark brown or black flakes with sharply defined edges, they come from the inside of the nozzle: burnt material from the inner edges of the nozzle, or from around the area where teflon-coupler and nozzle meet. Solution is atomic pulls, and if necessary replace burnt and deformed teflon coupler.

If they are bigger and lighter brown spots, without sharply defined edges (more looking like dark honey), they come from the outside of the nozzle: material that has built up around the nozzle, and then slowly burns and leaks down on the print. Especially if you have a bit of overextrusion, have increased the flow-rate, or if the first layer is squished really hard on the glass plate.

Solution for the second is difficult: pausing print and cleaning the nozzle-outside sometimes helps, lowering temp sometimes helps, but often not.

Also, lowering travel speed to the same as the printing speed sometimes helps: then during travels, the nozzle does not drop "morse code" bits on the print, which would on the next pass get picked-up by the nozzle, accumulate, and cause this dripping. But at lower travel speed, you may have a bit more blobs when traveling through air.

[tomnagel 126]

Has anyone ever tried to put some (silicon?) oil on the outside of the nozzle? I'm guessing it would prevent material to stick to the nozzle.

[yellowshark 153]

I wipe the nozzle with isopropyl alcohol and it does exactly as you ask 8)

[geert_2 558]

Has anyone ever tried to put some (silicon?) oil on the outside of the nozzle? I'm guessing it would prevent material to stick to the nozzle.

For some unknown reason, my reply was eaten up by the system and didn't show up on the page. So, let's try again.

I use silicon mould release oil: spray it on a tissue and wipe the nozzle. This reduces build-up of molten filament on the outside, but does *not* eliminate it. It depends on the material: it works less or more for PLA, but does not work well for PET, which is much more sticky and "rubbery" when molten.

I also tried PTFE oil, which also helps a bit, but less than silicon oil.

I haven't tried any other oils.

Some time ago, there was a thread in which this was discussed, if I remember well it was about putting silicon socks around the nozzle, for the same purpose.