Arcol hot end variable extrusion width during print

I have been following these instructions [www.thingiverse.com] for calibrating my
-Mendel Prusa with
-Ramps 1.2 electronics
-kliment kip firmware (set so 1 extrusion unit is 1 mm of filament)
-repsnapper 03.28.11
-skeinforge 40
-running the hot end at ~270C

On the section where I am calibrating the width over thickness I am noticing a huge amount of variation in the amount of plastic that seems to be coming out of the nozzle from the base (where it extrudes too much) to the top (where it extrudes very little). I currently have my width over thickness ratio set to 2.

I watched the voltage supplied to the heat core on the hot end and I don't believe that its a lack of heating causing this but i could be wrong.

Thank you for your help,
ftc

270 C seems too high for either ABS or PLA. What are you extruding? I have clogged 2 nozzles by setting my tip to 260 C and letting it sit there too long.

I am extruding ABS, I am hesitant to believe that this is the issue though since it extrudes fine initially then later on is when it seems to act like it might be clogged or something.
Thanks for the idea I will try dropping my temperature to ~250 and see what happens.

... if you overheat ABS, then it went harder (recrystallization or carbonisation) and will start to clog the nozzle, so this should be the issue ...

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One of the regular failures I initially had with my hot end (not Arcol but a PTFE/PEEK hybrid) was when the extruder had been on for a while the PTFE/PEEK section would heat up enough to soften the feedstock inside the thermal break (PTFE). Then, because the barrel inner diameter was 3.2mm and the PTFE inner diameter was 3.5mm the plasitc in the PTFE would swell under the pressure from the extruder driver to the diameter allowed by the PTFE (3.5mm). This then would be too big to enter the barrel(at 3.2mm) and would result in the feed mechanism slipping...

I have replaced the PTFE section with a new section drilled out to 3.2mm and have no more problems of that type.

[edit] - keeping it in one thread as Sebastian asked

Edited 1 time(s). Last edit at 04/19/2011 06:54AM by AgeingHippy.

Of course, the licence the Arcol is under
Let's keep it in one thread, please.

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Remember, you're all RepRap developers (once you've joined the super-secret developer mailing list), and the wiki, RepRap.org, [reprap.org] is for everyone and everything!

Thank you for the suggestions I think this all points to the first step being to fiddle with the temperature until it is working a bit better. If that doesn't work then I will try some other things like drilling out the peek.

Hey ftc

Don't drill out your PEEK !!

I doubt that is where your problem is. My problem was with the PTFE=white stuff (as opposed to the PEEK=brown stuff) and the hole was too big not too small...

lol - I am probably jumping the gun here and you probably spoke hastily but knew what you were meaning

Ah yeah, i meant to say that I would drill out a new piece of peek but my mind skipped around a bit there, thanks for the clarification though.

So I tried dropping my temperature to 255 and the problem seems to be worse. [desktop.alephobjects.com] I am not entirely sure that my thermistor is calibrated so I was not paying too much attention to the temperature itself, more what it looked like as it came out.
Thank you for the continued help.

I think I may have figured it out, looks like my Arcol had a bit of a cholesterol problem: [desktop.alephobjects.com]
Does anyone know if the PTFE piece can just be made out of the same block as the PEEK? Or does the plastic stick to the PEEK more than the PTFE?

Have a look at my hot end. It uses a1/2 inch diameter, 40mm piece of PTFE drilled 3mm. The PTFE rod is screwed into the end of a brass coupling, where 10mm of the end of the PTFE has been turned or sanded down to 8mm. When I screw this onto the coupling, it actually compresses the 3mm hole a bit.

When the filament, ABS or PLA, travels down through the PTFE, it is warmed to about 100-125C, and it only comes in direct contact with hot metal when it hits the MIG welder tip at the end. There, it heats up pretty quick, and it's a very short run to the nozzle hole. This design eliminates most clogging issues you might see in the other designs with long metal barrels.

One thing to mention: When I run PLA at 200C, it actually comes out of the nozzle at around 165C. I suspect that ABS acts similarly. I used a thermal camera to take the measurements, so I'm pretty sure this is correct.

@jcabrer would you mind submitting that link again, it seems to be broken and I would very much like to see the setup you have.

jcabrer Wrote:
-------------------------------------------------------

>
> One thing to mention: When I run PLA at 200C, it
> actually comes out of the nozzle at around 165C.
> I suspect that ABS acts similarly. I used a
> thermal camera to take the measurements, so I'm
> pretty sure this is correct.


How accurate is a thermal camera? I thought that it was limited by the low resolution and also the fact that it only measures surface temperature. Can it accurately measure filament temperature?

The FLIR SC-6000 is very accurate!$$$ ;^) I drilled a hole in the PTFE tube to peek inside (no pun intended).

I haven't quite got the hang of using the wiki, so the much nicer writeup for my hot end is on thingiverse.

Here are both links, for now. Keep in mind that I'm constantly tweaking, but the main concept is still the same. One down side is that Harbor Freight, my suppier for the 1/4" AUTO BRASS COUPLINGS quit carrying them, and I have no information on the manufacturer. I think they went out of business. In any case, I can only find these couplings in steel now, and haven't tested one yet.

[www.thingiverse.com]

[reprap.org]

jcabrer, You say in your instructions on thingiverse:

"1 - 1/4" Brass Auto Hose Female Coupling (these are a little different from air hose couplings) with 1/2" ID on the large end."

How are they different? What is an auto hose coupling? Basically, what does it connect?

The brass air hose fittings are available lots of places. Can they be used? Guess I could answer my own question by just trying one, but if you've already tried I'll not reinvent the wheel this time.

Always looking for hot ends. Will be building one soon, I hope.

The normal brass couplings have a thin lip near the tip. This is where the quick disconnect barrel grabs on. On the Automotive couplings, this lip is wider, which provides greater surface area contact between the aluminum block and the coupling tip. I suppose one can sand down the lip and just drill a smaller hole in the aluminum block.