Extruder feed problem (SOLVED)

Hello All

I have an extruder based on Adrian's Geared extruder. In fact it may be Adrian's geared extruder.

The hot end is one of reifsnyderb's hybrid PTFE/PEEK thermal breaks with a big head and a heater block of my own construction.

My problem is that I can get a bit of feed going but very soon although the extruder continues oozing the M4 insert will chew a concave section into the feedstock and I cannot extrude any more.

I have tried tightening the gadget that squeezes the filament between the bearing and the M4 insert to the point where the filament is horribly deformed when all is running fine but this still seems to occur.

It seems the filament swells slightly in the insulator just before it gets to the brass barrel and then is too big to enter the barrel.

I wonder if anyone can advise. Obviously the hole in the thermal break must be slightly too large allowing the PLA to swell.

Does anyone have any thoughts about how I can overcome this - has anyone else experianced anything like this?

How much pressure should be placed on the filament when pinching it to the M4 drive insert?

EDIT: 2011/02/13 (That's yyyy/mm/dd for the Yanks )

The action I took as listed further down in the thread seems to have solved the problem and the extruder seems to be working fine.
Essentially I drilled out the entrance of the barrel to 3.5mm (from 3.1mm) to a depth of about 7mm. This allows any bulging section to enter the barrel and melt enough to allow me to extrude. I mentioned below that retract the filament by about 15mm at the end of a print. That seems to be unnecessary.

Edited 1 time(s). Last edit at 02/13/2011 04:48AM by AgeingHippy.

Without a photo, it's hard to know for sure. But perhaps you wound the nichrome wire too far up the hot end. Also, is it possible that you're thermistor table is the wrong one and your temperature is too high?

Hey brnrd (??)

The heater block (as opposed to nichrome) is about 15mm from the bottom of my thermal break.

I was just wondering about the temperature perhaps being too high. I have nasty ooze at 190 and can still push plastic through when my temperature reads 180 although it seems a little more difficult.

The hole in the thermal break is indeed bigger (maybe 4mm) than the barrel so I wonder whether I am wasting my time trying to proceed with this thermal break and perhaps I should source another with closer tolerances... comes from buying parts from someone who does in fact not have a reprap to prove his stuff on first. Perhaps I am being unfair - does anyone else have this problem with reifsnyderb thermal breaks?

OK. My extruder oozes a lot also with PLA even at 190, so you're temperature might not be too far off. I have mine set to extrude at 205 and I haven't experienced the same problem after going through about 4 lbs of PLA.

BTW, I highly recommend putting springs on those 4 bolts on the geared extruder to apply constant pressure. I used a longer set of M4 bolts on mine and it works quite well.

AgeingHippy:
If you checked the diameter before use, you should see that it is closer to 3.35 mm. With the barrel ID at something like 2.99 mm, the PTFE is drilled out larger. I think he based his dimensions off of the official build spec though and they do work as long as the PTFE does not expand.

If your ID is closer to 4mm, then I think it is more likely that your PTFE wasn't constrained well enough and has expanded. If you are using a wade type extruder with the top 10mm or so inserted into the extruder block, my experiance has been that the top part must fit VERY tightly or it will expand. I re-shaped a junk PTFE insulator to fit inside of a pipe coupler. Since I left the OD of the insulator a bit larger than the ID of the fitting, it forced the inner diameter and threaded section to constrict back to their as-drilled diameters and it worked again. I attached some pictures of the PTFE stuffed into the fitting so you can see what I'm talking about.

The round section was actually the perfect diameter for still fitting into the cavity on my extruder block, but it was a major pain getting the PTFE shaped to fit inside it. It wasn't quite tall enough to fill the cavity, so I had to use some PTFE slices off the bottom to fill the air gap. I quit using it because the stack up proved to be too unstable. However, the general concept will fix a deformed insulator - you just need a fitting that won't leave you with an air gap.

This is odd because Brian sent me samples of his hybrid and they worked fine once he added the circlip to stop the PTFE moving upwards. The hole in the PTFE is about 3.5mm and so is the hole through the barrel.

You could drill out the top of the barrel to match the diameter of the PTFE.

Edited 1 time(s). Last edit at 02/06/2011 04:48AM by nophead.

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[www.hydraraptor.blogspot.com]

My hybrid hot end from Brian never had any such blockages but did die with the typical hot end failure mode:



I now use a hybrid from Stoffel15 who is located in northern Germany:



This has been working very reliably for me.
It is basically Adrians' current design where the PTFE is screwed into the messing hot-end only Stoffel15 uses PEEK with a teflon (PTFE) sleeve inside.
It has the advantage of not needing the two 4 mm studding/screws to restrain the PTFE and of course uses nophead's heating block.

It is short, small and reliable!

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

Hmm...

What you guys said triggered a little light in my head.

When pushing my feedstock through the thermal break (even without the barrel attached) there is resistance at the point of PEEK/brass interface. The PEEK constricts at that point - possibly because in the past when I did not know what I was doing I tightened the barrel into the PEEK very tightly - obviously deforming the PEEK.

I will drill that section out to 3.5mm (the rest of the PEEK is 3.5mm, not 4mm, according to my callipers). The barrel reads 2.9-3mm so I might drill a cm or so out to 3.5mm... first I will try just doing the PEEK.

Will give feedback once I have results.

Does anyone know how long the 0.5mm section is on Brian's bighead nozzle? The tip seems to protrude by about 2mm. unfortunately the inside is now full of plastic so I cannot see how deep any recess is from the inside. I am under the impression that the longer the orifice section is, the higher the required pressure to extrude. Is this correct?

I may grind the tip down to about 0.5mm if the orifice is not recessed from the other side and if doing so makes sense.

later

@rhmorrison,

What is the step visible at the end of the PEEK? The end of my two samples is flat.

@AgeingHippy,
PEEK/brass interface? Do you mean PTFE/brass?

The way my samples were constructed the brass tube screws through the PEEK and butts up against the end of the PTFE section. If I over-tighten it the PTFE will constrict. I put a 3.5mm dill shank in it and tighten it until it just starts to grab the drill.

Yes the pressure to push the plastic through the final part of the nozzle is proportional to the length. However, a lot of the force required to push the filament does not come from the nozzle pressure, it is pushing the plug of very viscous plastic at the transition zone. If you do grind it down you will need to remove the burr with a drill the same size as the nozzle.

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[www.hydraraptor.blogspot.com]

Rhmorrison, will hose clamps fix the "typical hot end failure mode"?

@nophead: It is the PEEK, he designed it with a step in it (at least the newer versions). If you are interested I can take some better closeup pictures of it.

Edited 1 time(s). Last edit at 02/06/2011 12:33PM by rhmorrison.

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

No need for photos thanks.

The first one I had leaked like that because the PTFE slipped up the barrel. I have used the second one that has a circlip for some time at temperatures up to 255C and not had any problem. The seal is formed by the brass pressing into the PTFE a little. That is why I screwed it in until the PTFE started to constrict. When it heats it should get a bit tighter if anything.

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[www.hydraraptor.blogspot.com]

Just to give some feedback. I drilled out my barrel to 3.5mm for a depth of about 7mm and also reamed out the constriction at the PTFE (thanks Nop ) Brass interface.

I also tend to retract about 2cm of feedstock when I am done printing to reduce ooze and also to attempt prevention of blockage when I next heat up and run the extruder.

This seems to work.

AgeingHippy Wrote:
-------------------------------------------------------
>
> I also tend to retract about 2cm of feedstock when
> I am done printing to reduce ooze and also to
> attempt prevention of blockage when I next heat up
> and run the extruder.
>
> This seems to work.

I don't do this and I haven't had a blockage. Of course I just started about a month ago but I'm almost through with 5 lbs of feedstock. The only time that the filament got stuck on me was when I tried to remove the filament by retracting it while the extruder was hot. It got to a point where it stopped retracting. I found that at that point, I couldn't go forward either. After taking the cold end apart (Adrian's geared extruder), I found that there was a bulge between the filament drive and the hole where the filament goes into the hot end.

Yes - I retract only enough to avoid the soft plastic. The retraction also tends to streach the hot plastic a little so any bulges due to feed pressure are removed...

Possibly not neccesary, but seems to work for now.

You don't want to retract the filament 2cm at the end. If you allow air into the barrel the plastic will oxidise and leave a hard deposit behind.

PLA always oozes during warm-up, but with about 1mm of retraction it doesn't ooze during printing as long as you don't have it too hot.

To start a build I warm up and than extrude about 10 cm of filament into to the air. I remove that and start the machine. The first thing it does is descend to the bed and extrude a blob, from there it draws a rectangle round the object and then starts the build. During the time it takes do descend it may ooze a few mm but that gets hidden in the blob which also ensures there is no deficit and the thread is anchored. The rectangle shows me the position of the object, how level the bed is and how even the flow rate is.

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[www.hydraraptor.blogspot.com]

Another very useful thread for me to read - thanks all!

@ Aging Hippy

I'm now planning on tracking back through all your posts - it's amazing / suprising how many similar issues I am having. Very glad to be having them after you've already worked through them :-)

@ RHMorrison

You're PEEK break with threaded brass nozzle is not constrained vertically (z) ? I have been thinking along similar lines and have threaded a nozzle directly into some PEEK rod with a PTFE liner (not yet tested / finished) but was concerned that the PEEK support block and 4mm studding was necessary for z axis constraint.

No thermal expansion issues with your hot end? Any warnings or advice you could offer to me as I head down that path? :-)

@ Nophead

Thought something like this was happening but couldn't figure on it exactly. I'm using PLA and have had problems with a wades extruder jamming after the hot end has become blocked. Dismantling and painful extraction of the filament has led me to finding a bulged section of filament too but I couldn't understand why heating to 220 plus wouldn't clear it out ..

Oxidised PLA is harder / has a higher melt temperature? Have you a good method of clearing it when necessary?


Nophead wrote ..

>
> You don't want to retract the filament 2cm at the end. If you allow air into the barrel the plastic will oxidise and leave a
> hard deposit behind.

@ RHMorrison

Mendel Parts V6 has the PEEK with PTFE lining thermal break but still maintains the pushfit design with the extra PEEK support block. I think that may be what got me to worrying that I'd still need the support block ...

The hot end design I am using is somewhat similar to the Mendel Parts V6 with one big exception, in my hot end the PEEK screws into the hot end whereas in the V6 the hot end screws into the PEEK. For PFTE this would NOT WORK for long. Since PEEK has little thermal expansion in comparison to PTFE it seems to work. With the PEEK screwed into the hot end it is guaranteed to work.

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

Quote

Oxidised PLA is harder / has a higher melt temperature? Have you a good method of clearing it when necessary?

Not really. I can't remember having a hot end jam in the last year. I clear a blocked nozzle by pushing a small drill up it while hot. I clear worse jams by running the heater and using a long shaft 3mm drill to rake out the molten plastic. In both cases I twist the drill by hand.

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[www.hydraraptor.blogspot.com]

evans2481 Wrote:
-------------------------------------------------------
>
>
> Thought something like this was happening but
> couldn't figure on it exactly. I'm using PLA and
> have had problems with a wades extruder jamming
> after the hot end has become blocked. Dismantling
> and painful extraction of the filament has led me
> to finding a bulged section of filament too but I
> couldn't understand why heating to 220 plus
> wouldn't clear it out ..
>
> Oxidised PLA is harder / has a higher melt
> temperature? Have you a good method of clearing it
> when necessary?
>

I had the same symptoms on two nozzles (0.5 mm) that got clogged. I think it happened when I the temperature got above 260 C with ABS and stayed there for a long enough time to decompose the plastic. The cruddy stuff won't melt anymore or dissolve in acetone. I don't know if the same can happen to PLA. To clear the nozzle, I used a blow torch and rubbing alcohol as shown by spacexula on youtube.

Thanks for the replies. Will check out Spacexula's clearing method on youtube. I have a blowtorch and not nearly enough excuse to use it :-)

And in the meantime I'll stick to the hand-twisting drill method ..

@rhmorisson - thanks for the link. Might get one shipped out to sought out my problems. Having fun fiddling with the extruder but it'd be nice to be printing at the same time.

Here's the link to spacexula's (repraplogphase) video: [www.youtube.com]

Using a drill works for the 3 mm section of the nozzle, but not for the tip which is only 0.5 mm or less.