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I've been trying to print a water bottle out of PLA (9.5 inches tall). The object has some brown spots like it was burned. The nozzle was cleaned with a blow torch before the print on the small object.

[img]http://i.imgur.com/r7exfzB.jpg[/img]

[img]http://i.imgur.com/Ea1bYnr.jpg[/img]

The problem is only noticeable with clear PLA. Has anyone else had this problem?

Could it be that the nozzle is rubbing PLA debris onto the print? Would a nozzle shaped like this help?

[img]http://i.imgur.com/28HJhrV.jpg[/img]

I can't see the pics right now, but there are objects you can print that are intended to hold uh... something..I forget if it's just cloth or a piece of sponge, anyways, to hold whatever it was and wipe down the filament before it goes into your extruder.

(remember I'm guessing because I can't see the print) If it is not excess PLA getting picked up by the nozzle each pass, heating up and turning brown, and then depositing into the print once it builds up enough, then try lowering your hotend temperature when using that specific filament.

Someone from #reprap suggested that there may be burned plastic inside the hot end before the nozzle

Disassemble the hot end, including unscrewing the PEEK and everything else. You probably have some old burnt PLA hiding up in there. It may also be your hot end cooling is right on the edge of letting it jam, so on long prints perhaps some of it is jamming up and burning. I say this all the time, but if you're printing PLA look into a Budaschnozzle or E3D. The SeeMe hotend is good for ABS... not so much for PLA. My blood pressure went down when I upgraded.

Now that I can see the pictures... it looked like in the partial shot there was a string of brown up multiple layers like it was doing it at a seam, is that just my imagination or is that actually there?

I disagree that the stock hot end isn't good for PLA. I've got over 190 hours on mine and I've NEVER had a jam with it. The longest single print was seven hours.

g.

geneb wrote:I disagree that the stock hot end isn't good for PLA. I've got over 190 hours on mine and I've NEVER had a jam with it. The longest single print was seven hours.

You sure it never jammed on you, even once?

The hot end I have in service now? NOT. ONCE.

The only time I've EVER had jams with PLA was back before I had a fan on the PEEK section. Since then, zero issues.

g.

Then I want to know what kind of fan setup you used, because I tried one and even two fans blowing across the PEEK and it jammed all the time. Even with other hot ends, if I leave the heater on after a print for more than a couple of minutes I have to pull the filament out of the top and clip off the melted part.

I use a single 25mm fan wedged between the melamine ring that the hot end is attached to and the effector platform. With the build of Blue Max, I've installed the SeeMeCNC PEEK fan shroud, but I haven't run any PLA on that hot end yet.

If you're getting those kind of jams, you might want to consider replacing the PTFE liner in the hot end.

g.

I used a 20mm fan, then two, blowing across the PEEK section. I stopped using the hot end a month ago so I'm all set.

I roll a buda with no fan PLA only and Ive had only 2 jams ever, because I was printing too slow, and because my stepper drivers were overheating. I solved that by optimizing my print settings and putting some heatsinks and a fan on the drivers. I've even ran a really old SeeMe hot end that came with an H-1 without a fan for 10 hours with PLA and the print came out fine, no jams (also many other prints with it as well). You guys and your silly fans.....

Nylocke wrote:I roll a buda with no fan PLA only and Ive had only 2 jams ever, because I was printing too slow, and because my stepper drivers were overheating. I solved that by optimizing my print settings and putting some heatsinks and a fan on the drivers. I've even ran a really old SeeMe hot end that came with an H-1 without a fan for 10 hours with PLA and the print came out fine, no jams (also many other prints with it as well). You guys and your silly fans.....

I can believe the Budaschnozzle might be capable of that, but not a SeeMe hot end with no active cooling. Where are you getting this PLA that can go through an uncooled hot end for ten hours without jamming? I've tried SainSmart and a couple other vendors on Amazon and never seen anything approaching that. I doubt my old hot end would last more than ten minutes without a fan, and it jammed even with that.

I'm going to have to go with Gene on this one guys, I rarely ever had my stock hotend jam when printing PLA......and I ran no cooling fans on the peek.

The secret is don't overheat the thing, if you suspect you may have come close just unthread the peek from the top and bottom aluminium and see if your linear is still intact top to bottom. So it doesn't allow any cavities for the PLA to pressurize itself into and then cool/heat jam.

I think it's a very drooly sloppy hotend at high speeds and at it's limits as far as temp goes, but it is not easily jammed badly. Many times I was able to unjamm it simply by backing the filament out 5, then in 7, out 5 in 7. And this cleared the jam easily.

A jhead will jam on ya far less then that however. And I would call it's jam's more of a slight hold up, lol.

For the buda I was using maybe some ultimaker white 3mm, the SeeMe was running with some cheap bulk order chinese stuff I think.