Extruder qeustion

Ok, I think I have narrowed down my last few problems..... I am down to what I think is the last one... When I wrap the nichrome wire should I do double layers to stay close to the tip? My first try I did not and it seemed to get to hot near the top which created a sort of plug near the top when extrusion was slowed or stopped preventing a restart. I would then need to remove the pinch bearing and pull the plastic and nip off the "plug" that was created.. I could then actually start again until I slowed or stopped...

Any thoughts or ideas will be much appreciated!

Dan

try it, report back!

Brass is a good conductor and there isn't much temperature difference over the length of the barrel. When extruding ABS we extrude at 220-240C but ABS melts at 110C so it all molten within the barrel. The plug is created in the insulator where the temperature drops below the melting point.

Double layers of nichrome near the bottom of the barrel are pointless in my opinion.

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[www.hydraraptor.blogspot.com]

Fair enough. Any thoughts to a solution? Many people use the standard design in the beginning to get started right? How this overcome? Maybe I have a different problem?
Thoughts?
Thanks!

Normally the plug is about 5-10mm in the PTFE insulator. That is very slippery, so as long as you have a seem-less joint with the brass, the extruder should be able to push it.

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[www.hydraraptor.blogspot.com]

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nophead
Normally the plug is about 5-10mm in the PTFE insulator. That is very slippery, so as long as you have a seem-less joint with the brass, the extruder should be able to push it.

YES, this is true for PTFE, but not for PEEK.

I have been playing around with my extruder hot end for weeks now and found that my primary problem was the switch from a PTFE insulator to a PEEK insulator. With the PEEK I get a blockage each and every time that does not occur with a PFTE insulator of the exact same dimensions. I can only ASS-U-ME that it is because PEEK has a much higher coefficient of friction than PTFE (i.e. it's not nearly as slippery).

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Yes I could never make PEEK work as a simple drop in for the PTFE design although others reported that they could. The only way I made PEEK work was using a short length with a taper and using a heatsink. My impression is that PEEK is a lot less slippery and also not as good an insulator as PTFE, but I can't find any figures that back that up.

[hydraraptor.blogspot.com]

I think the simplest solution to make the standard extruder design work is Brian Reifsnider's Hybrid design where he has a PEEK tube with a PTFE liner to combine the best of both. The only issue I had with that was the top end got too hot for PLA when running over a heated bed, but that may be because my heater is a large block of aluminium and is not insulated. If I had added insulation I expect it would have worked. I have stopped printing PLA though because I think a machine made from PLA is a bit like a chocolate teapot if you want to extrude ABS.

The BfB extruder also uses PEEK with a PTFE liner and that seems to have a good reputation for reliability.

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[www.hydraraptor.blogspot.com]

I just picked up my package from the Zollamt (customs) this morning with two of Brian Reifsnider's Hybrid design extruder hot ends (with 0.5 mm nozzles). However, I want to use them for my 2nd Mendel where I also want to try Adrian's geared extruder design as I am tired of having to remove the motor and the gear every time I need to work on the hot end. With Adrian's design it would appear that this is not necessary. Plus my 2nd Mendel will be made out of ABS RP parts so I can finally add a heated bed for printing ABS. My current Mendel (that is almost printing) has PLA RP parts and as such can not really be used to print ABS parts.

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Great info! I currently have the PEEK insulator installed... I will switch to the PTFE and report back... (I also just ordered the hybrid version as well) VERY frustrating stuff.... I almost had it working,,,,,,,,,,sooo what dissolves epoxy

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sooo what dissolves epoxy

It would seem that water does, as I have found to my cost, but it takes a long time, weeks.

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[www.hydraraptor.blogspot.com]

Pliers worked broke it free just fine.....I'll build the new one tonight!

its weird but it appears to work! PEEK=fail PTFE=pass
Thanks~~! now on to tweeking the software~!



I will update with detail when I know 100% (for people like me who beat their heads on the wall!)

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DanielG
PEEK=fail, PTFE=pass

This knowledge cost me three weeks of time to obtain!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

> I could never make PEEK work as a simple drop in for the PTFE design although others reported that they could.

Could it be that differences in making the heat barrier account for the problems?

If the hole of a heat barrier is slightly offset from concentricity of the brass tube, or a little conical (tip to the bottom), it could block a formerly molten piece of filament from sliding.

And a molten and then cooled down part of filament will probably fiercely cling to any little roughnesses which could be found in the hole because it has molded itself against and into it, so the hole has to be really smooth, no scratches from making it or from ripping out stuck filament parts or so.

Edited 3 time(s). Last edit at 07/28/2010 09:12AM by peer.

Well yes the join where the barrel meets the insulator has to have no gap and be well aligned, but I am always careful to make mine like that.

The soft plug of plastic expands outwards, so with a perfectly smooth bore, the coefficient of friction determines how easy it is to slide. There is a critical threshold beyond which it will jam solid, no matter how much force you apply because the force you apply creates the pressure on the walls and the friction is proportional to that pressure. So the more you push, the more resistance there is, positive feedback. It effectively forms a ratchet such the filament can only be pulled, not pushed.

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[www.hydraraptor.blogspot.com]

I am tweeked! printing my first part right now!.. its a bit of a train wreck but its printing! my steppers are off by 2 mil or so but its printing!
Now i just need tuning!<<<< errr and a new stepper.... extruder stepper failed as i was typing... no matter..< I think its been my problem the whole time... funn stuff...