Brown dots in filament

Hello,

in a print, which stopped accidently due to a power loss at the first layer, I spotted some brown dots in the printed filament at several places of the first layer. The dots are also visible from the bottom side.
The print is made with white PLA, extruding at 185°C over the heat bed set to 65°C.

The PLA is from a new spool of a brand I'm using the first time. So I'm wondering, if this brown particles originate from the PLA or from debris from inside of the hot end.

Cheers, Gerd

The most common cause is a bit of filament curling onto the hot end, burning and then dropping off again, particularly if it is just the first layer that is affected. I always scrape the hot end with my fingernail before starting a build to remove any loose crud.

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[www.hydraraptor.blogspot.com]

I think, its a combination of two effects, the curling and burning effect (I have actually some problems with curling) and the debris from inside of the hot end.
I extruded some filament into free air and it was curling much. Also the extruder stuck some times for a part of a second, obviosly when a particle of debris passed through the nozzle.

So I pulled out the filament manually at 80°C some times (photo) and that moved some debris from inside. Afterwards I removed the hobbed bolt and tried to push filament manually through the nozzle. I needed much pressure, even when rising the temperature to 220°C, and the filament was curling much.

So I assume, I have to clean also the nozzle outlet. On monday I will buy some steel guitar strings to try this. I'm not shure how looks the inside shape of the nozzle: is it better to insert the string from upside or from below?

Edited 2 time(s). Last edit at 03/01/2014 06:35PM by GerdH.

There is a cone leading to the exit but I always ream it upwards from below.

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[www.hydraraptor.blogspot.com]

Still struggling with the hotend ...

I reamed out the nozzle with a guitar string, which helped for a short time, I pulled out the PLA filament several times at 85°C, changed to another type of natural PLA, but nothing was succesfull.
The extruder every time stucks again after a short period and I need to disassemble the extruder, clean the hobbed bolt etc.

I there a way to clean the J-Head from the upper side bore, e.g. with a drill?

Using the pull back at 80C method you should be able to completely empty the barrel, shine a light up the nozzle and see that it is completely empty.

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[www.hydraraptor.blogspot.com]

Finally I achieved to clean the hot end completely!

I removed the hot end from the extruder, put it to a vise and heated it up. Then I reamed out the nozzle by a guitar string.
But afterwards it was still not possible to look through. I pushed a 3mm drill from above into the hot end, but it moved forward only to about 1cm above of the brass part of the hot end. A 2mm drill I could advance down to the nozzle.

I tried then several times the pull-out method with PLA at 80°C but I could not extract all of the filament in the hot end. At least I still couldn't push the 3mm drill down to the nozzle. May be there was still some ABS filament sticking to the wall inside of the hot end from former prints.

After that I heated up the hot end to 220°C and pushed the 3mm drill into the hot end down to the nozzle. Wenn I removed the drill at a lower temperature some additional filament came out with the drill. I repeated this procedure several times , until I could push in the 3mm drill also into the cold hot end. Then I reamed out the nozzle another time using the guitar string.

After that I could print out a 4h PLA part without problems!

Thanks for all hints and advices!

Cheers, Gerd

Ah yes, when you switch between different types of filament you have to flush it through at the higher of the two temperatures until it comes out pure. Otherwise ABS can block the hot end when it is running at PLA temperature.

Edited 1 time(s). Last edit at 03/05/2014 08:39AM by nophead.

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[www.hydraraptor.blogspot.com]