Hot-End and Extruder Choices

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Re: Hot-End and Extruder Choices

Postby flickerfly » Tue May 07, 2013 1:27 am

I just found this wiki page about the QU-BD extruder: http://www.buildlog.net/wiki/doku.php?i ... provements

It sounds like bdring didn't need to do the machining on his QU-BD, at least at the last editing of that document. It makes me wonder if I regularly cleaned out the hot end by dropping a bit of acetone in the top before printing each day if I could get away without drilling out the nozzle. Any ideas on that?
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Re: Hot-End and Extruder Choices

Postby Winder » Tue May 07, 2013 12:20 pm

flickerfly wrote:I just found this wiki page about the QU-BD extruder: http://www.buildlog.net/wiki/doku.php?i ... provements

It sounds like bdring didn't need to do the machining on his QU-BD, at least at the last editing of that document. It makes me wonder if I regularly cleaned out the hot end by dropping a bit of acetone in the top before printing each day if I could get away without drilling out the nozzle. Any ideas on that?


I have successfully printed with PLA continuously for over 3 hours. Now I only get jams when the fan stops working or it stops extruding for too long. I expect that drilling the barrel and using PTFE would help with these last problems so I'd still like to do it eventually, just having too much fun with my printer to take it apart again right now. :)

My modifications:
1. Upgraded idler with one from Bart's store.
2. Hobbed the raptor gear with a small tap.
3. Applied thermal paste between the Qu-bd cold block and the fan
4. Put a thermal break between Qu-bd cold end and the extruder motor using a print that failed after the first layer or two. (my extruder stepper gets very hot, I've turned its driver pot down so the motor no longer gets too hot to touch, but it still gets quite warm).
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Re: Hot-End and Extruder Choices

Postby flickerfly » Tue May 07, 2013 12:39 pm

Thanks Winder. I appreciate you sharing your experience.

Do you know of any diagrams that show which parts are which on this extruder? I'm not entirely sure I can accurately identify everything you mention. :?
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Re: Hot-End and Extruder Choices

Postby Winder » Tue May 07, 2013 3:49 pm

flickerfly wrote:Thanks Winder. I appreciate you sharing your experience.

Do you know of any diagrams that show which parts are which on this extruder? I'm not entirely sure I can accurately identify everything you mention. :?


Here is the best picture I have on hand. The black block between the stepper motor and the heatsink is what I called the cold end. On the right you can see some thermal paste squeeze out between the cold end and the heatsink. On the left the white poking out between the motor and that block is a thin layer from a failed print which seems to help keep the motor heat away from that cold end.
Attachments
extruder.jpg
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Re: Hot-End and Extruder Choices

Postby flickerfly » Wed May 08, 2013 2:12 am

Okay, that helps. Thanks winder! One last question, what do you mean by "it stops extruding for too long". Do you mean you just don't print something for a few days?
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Re: Hot-End and Extruder Choices

Postby Winder » Wed May 08, 2013 1:15 pm

flickerfly wrote:Okay, that helps. Thanks winder! One last question, what do you mean by "it stops extruding for too long". Do you mean you just don't print something for a few days?


Like a pause during the print when the filament isn't being extruded. My best guess is the filament starts to melt/expand too high in the barrel which causes it to get stuck. This is one area where the PTFE mod would really help.
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Re: Hot-End and Extruder Choices

Postby cvoinescu » Wed May 08, 2013 3:42 pm

My hypothesis is that this happens: more filament than usual melts at the bottom end of the barrel. When extrusion resumes, the still solid filament plunges into the molten plastic, and displaces it. It flows up between the filament and the walls of the barrel, where it freezes, jamming the filament in place. Two factors make this worse with PLA: it flows particularly easily, as opposed to ABS which is quite viscous; and it contracts less as it hardens, so the solidified plug remains stuck in the barrel. With a slippery liner, the solidified plastic wedged between the filament and the liner just slides back down into the melting zone along with the filament. With a short and abrupt transition zone, only a small amount of molten plastic can rise before it solidifies, forming a shorter plug, which is easier to push back down. With a tight hole (which is usually the case with a liner), very little molten plastic flows up, and it solidifies after a very short distance. (Maybe all we need is a gasket, such as a tiny silicone or PTFE O-ring, not a full liner, and a slightly tapered melt zone, wider toward the nozzle. Or maybe not.)
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Re: Hot-End and Extruder Choices

Postby flickerfly » Wed May 08, 2013 5:16 pm

cvoinescu, where would you place the ptfe o-ring? At the bottom of the barrel?
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Re: Hot-End and Extruder Choices

Postby cvoinescu » Wed May 08, 2013 7:01 pm

It was just an unbaked idea. I'd put it above the melt zone. Too low, and you risk making a complete mess when the filament melts above the ring. Too high is probably not as big of a problem.
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Re: Hot-End and Extruder Choices

Postby REdington » Wed May 08, 2013 8:08 pm

cvoinescu wrote:a slightly tapered melt zone, wider toward the nozzle

I've made several barrels with a 1 in 50 taper reamer and it didn't seem to help with PLA. Maybe If I would of tried a 1 in 25 taper reamer, it might of worked. I'm done testing for now that I have the PTFE liner that works all the time with PLA. I do want to try printing with nylon and will see what happens then.


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