J-head melting when trying to print with ABS

My RepRap J-Head Mk-IV-B has melted for the second time now. Both times i have bin trying to print with black ABS plastic, I only ever get about one good print before some thing happens with this thing. It keeps getting all jammed. The hobbed bolt in my Wades extruder keeps ripping divots into my plastic because my tip has to much pressure built up in it (if i pull the plastic when extruding with out the hot end on it lifts up the reprap just fine so its not a bad idler pressure). I've tried printing at a few different temperatures i had it at 240c before, then i moved it up to 250c so that i could at least get a little bit of plastic to come out. But once i got it up to 250c it melted its self. What am i doing wrong?

Why not ask Brian direct here since he makes them

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Experimenting in 3D in New Zealand

Black plastic tends to have crap in it which blocks the nozzle.

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[www.hydraraptor.blogspot.com]

PM Sent.

Regards,

Brian

Forgot to add that PEEK melts at 248 degrees C.

When printing at .35, I only use natural ABS to be sure that my nozzle will never clog.

Benjamin Engel Wrote:
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...... I've tried printing at a few different
> temperatures i had it at 240c before, then i moved
> it up to 250c so that i could at least get a
> little bit of plastic to come out. But once i got
> it up to 250c it melted its self. What am i doing
> wrong?

I'm a rookie at this, and possibly quite lucky, but I've been printing black, red, natural & orange at 220-230 degrees, with my .35J-head, almost daily for the last month.

I was 'stripping' the filament on the knobbed bolt a bunch when I started, but that was before I got the z-height adjusted properly. Hasn't happened in a few weeks. I think blocking/dragging the nozzle would increase the force & strip the filament.

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Thingiverse ID Alan1279

that was my problem in the beginning. a wile ago, but then i did get it printing okay for about 3 prints and it was happening again. even if i lifted up my Z 10 so that it wasnt even touching my bed. i think i had messed up my tip by some how getting some thing stuck in there. so im soaking my old tip to clean it and i have a new one getting sent to me thanks to Brian. I'll post on here again once i try the new .5mm tip

I run PEEK nozzles up to 255C, including a J-head, and have never had the PEEK melt. That is measured inside the brass part. The ABS I use needs about 250C to bond well.

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[www.hydraraptor.blogspot.com]

If you suspect the nozzle is clogged, take the brass part off, and heat it up with a torch, or on a stove. Drop it in water while still hot. Inspect. Rpeat if required. Brian may have some warning, or disclaimer about this method.

Check the temperature reading by bringing the nozzle up to 100°C, and place a drop of water on the brass. See if it boils. If it does, bring the temperature down 5°C, and repeat. If it does not, bring the temperature up. Do this until you find the spot where boiling begins (altitude above sea level may affect this). This is not a precise measurement, but it does establish a repeatable baseline. If you can determine the variation between you teperature reading, and the actual surface temperature of the hot end, you may find that you were simply too hot, or too cold on your previous prints.

On a side note, I too have had ABS black that is impossible to print with. I believe it came from MakerGear. This was ages ago though, and they gave me a credit for it.

okay so i got the new j-head to replace my old end and its awesome! i got the .5 mm this time and my prints have been coming out grate! super smooth edges and the plastic is flowing out very well now. Best of all is that it has not melted on me. I've bin working with it at about 220 with absolutely nothing going wrong. Thank you every one for helping me out on this dont think ill be melting any other ends any time soon!

link to my blog talking about this and my fix a little bit more

sorry to bring up an old post, but i suffered from my j-head melting like shown in ben's blog photo (post above this one)

Is it possible to replace the black PEEK part, without having to order everything else?

Yes, as long as the rest of the parts are undamaged, you can replace just the PEEK insulator.

I know there are drawbacks, but I'm starting to think that a stainless steel hot end may be preferable to PEEK for working at higher temperatures.

GregSilver Wrote:
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> sorry to bring up an old post, but i suffered from
> my j-head melting like shown in ben's blog photo
> (post above this one)
>
> Is it possible to replace the black PEEK part,
> without having to order everything else?

@Gregsilver Where did you get the J-head from?

reifsnyder designed the j-head. his website is hotends.com. He sells all the components individually.

How on earth did you melt it? thermistor pop out?

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- akhlut

Just remember - Iterate, Iterate, Iterate!

[myhomelessmind.blogspot.com]

I think the j-head needs different PID settings than the default set on Sprinter or Marlin. I had a Mk IV-B and a V-B that were both overheating. On the V-B running on an older version of Marlin, I changed the PID the same settings that someone else had posted after he auto tuned with Marlin and it has stopped it from overheating. I'm about to switch the other printer to Marlin so that I can autotune the extruder.