Switching between PLA and ABS, thoughts on Under-extrusion, Clogging, Burnt PLA

[ccw1984 1]

So far I've been having a great time with my Ultimaker 2, but recently ran into an issue and I think I may have figured it out, but wanted to share my thoughts, hopefully a successful cleaning process, and to bring together some info and theories on material swapping, underextrusion, clogging, and burnt PLA together for discussion.

Background:

Printed nearly the entire spool of PLA that came with the Ultimaker 2, decided I wanted a lampshade and got some translucent ABS for that. Printed a nearly 30hr print in ABS (along with a few smaller pieces), which went fine. I decided to switch back to PLA (Red PLA from Push Plastic). I used the switch material option figuring that when it extruded again at ~240-250 the PLA would push any ABS out, but I started having underextrusion along with feeder clicking after lowering the temperature and switching the material back to PLA.

I assumed that I had a few spots of uncleared ABS inside the head, so I did an atomic pull with ABS, another atomic pull with PLA and both came out fairly clean. Looking through the extrusion hole with a light I couldn't see anything blocking it, and it looked circular (ie nothing stuck on one edge).

After fiddling with temperatures (figured maybe the red PLA needed a higher temperature) I was able to get an ok print by the end of it with a 95% flow rate, 225 C, and probably ~30-40 mm/s print speed.

Theory:

When switching from PLA to ABS normally, most of the PLA is pushed out, however some is left on the inside walls of the melt chamber and at the higher temps and long print time for the ABS part caused it to carbonize on the inside of the melt chamber, slightly reducing the available volume in the melt chamber and most likely the diameter of the nozzle.

What I think is happening:

Left: Printing Original PLA (blue), Middle: Printing ABS (grey) without clearing all PLA, Right: Burnt PLA (black) causing underextrusion due to lower melt volume & nozzle opening

 

A thermally stable residue was formed in all of the isothermal thermogravimetry experiments conducted at different temperatures. A possible explanation for the stability of this residue would be carbonization of the polymer sample during the experiment and the catalyst traces.

 

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.148.7599&rep=rep1&type=pdf

 

This is causing increased backpressure and the feeder clicking, which then causes underextrusion as it tries to "catch up" from not feeding for that second. Because the PLA layer is thin, carbonized, and stuck to the melt chamber pretty well, the atomic pull appears unable to remove it. Higher temperature makes the new PLA flow easier and lower flow rate effectively seems to simulate setting your nozzle size a bit lower.

Possible Solutions (In order of difficulty):

Atomic pull with ABS several times

Clean bowden tube (reduce friction)

Disassemble and burn out the print head

Atomic pull with Nylon 618 (higher temp, possibly 'stickier' to the residue, would have to order some)

Soak in chlorinated solvent/THF

 

Semi-crystalline poly(L-lactic acid) can completely dissolve in chloroform and dichloromethane. Amorphous poly(D,L-lactic acid) can completely dissolve in acetone, THF, chloroform and dichloromethane.

 

Links:

http://umforum.ultimaker.com/index.php?/topic/3600-what-works-best-with-cleaning-an-ultimaker-hotend-nozzle/

http://umforum.ultimaker.com/index.php?/topic/8935-best-way-to-clean-old-nozzle/

http://umforum.ultimaker.com/index.php?/topic/9221-underextrusion-blockage-what-do-i-try-next/

http://umforum.ultimaker.com/index.php?/topic/8972-clean-burnt-um2-nozzle/

http://umforum.ultimaker.com/index.php?/topic/4118-blocked-nozzle/

 

http://bukobot.com/nozzle-cleaning

 

 

 

[nick-foley 5]

Yeah, this is a pain and happens any time you switch from PLA to a higher temp material. When I switch from PLA to PET/XT, if the hotend isn't meticulously clean, the temperature increase and polymer change seems to knock off every bit of residue which has built up inside the hotend and cause a clog in a matter of minutes. Sometimes, you can just push through it, but usually, it requires a few atomic pulls with the higher temp material.

I just placed an order with PrintedSolid, but forgot to pick up some nozzle cleaning filament while doing so. I would hope that running a few cm of that filament in between material changes would make the swap easier. Will probably try it soon.

 

[ccw1984 1]

I tried multiple atomic pulls with the ABS filament I have (Gizmodorks transparent ABS) unfortunately: at 120 - 130C it either would NOT come out, or broke at the teflon connector without pulling anything out of the melt chamber. At 130-140 pulled out only a thin strand of ABS but nothing from the chamber walls like I was hoping. This ABS seems very brittle and will snap easily as I try to straighten it out for the atomic pulls.

Also I noticed that as I push the ABS past the teflon insulator there is a slight bit of resistance at the base of it, where the teflon part terminates into the melt chamber, is there supposed to be any resistance there or should it be completely smooth? I've heard plenty about deformed teflon pieces causing problems, but I've only had the printer since late Dec and haven't printed that much yet, but again this was after a ~30hr ABS print.

Next I guess I will be disassembling the print head and cleaning out the nozzle with acetone, fire, and perhaps brasso/metal polish as suggested to get it nice and clean inside.

the temperature increase and polymer change seems to knock off every bit of residue which has built up inside the hotend and cause a clog in a matter of minutes.

My issue seems to be more of a problem with volume reduction and the fact that the printer is still trying to force too much material through what is now a smaller volume opening, since it only underextrudes once the feeder stepper 'clicks' and skips back due to the pressure.

I just placed an order with PrintedSolid, but forgot to pick up some nozzle cleaning filament while doing so. I would hope that running a few cm of that filament in between material changes would make the swap easier. Will probably try it soon.

Have you had luck with nozzle cleaning filament before? Is it the Esun filament, or just nylon?

http://www.esun3d.net/cpxx.aspx?id=192&TypeId=26

 

[ccw1984 1]

Well, I obtained some http://www.amazon.com/Printer-CLEANING-filament-Makerbot-Printers/dp/B00O92RW92/ref=sr_1_2?ie=UTF8&qid=1422282125&sr=8-2&keywords=eSUN+3D+Printer+CLEANING over the weekend and ran some through the printer by hand. It doesn't really to do atomic pulls well, the filament is rather soft and so far has always broken at the sharp temperature change in the Teflon coupler when trying. However after running ~15-20mm of the filament through I am happy to say that so far it has been printing much better with only a few feeder motor 'hiccups'.

I think from now on I will take the advice I saw on one of these threads to basically do a 'cold pull' when swapping material, instead of using the standard 'change material' procedure on the Ultimaker. So manually heat the head ('heatup nozzle') to ~90C for PLA or ~130C for ABS and then remove the filament manually to get as much out as possible. And may go as far as to always put ~10cm of the Esun cleaning filament before the next material to clean it out.

 

[cloakfiend 995]

Just to let you know i think there is a problem with the cura, as when i print the raft in o.1 it is always fine, as soon as i switch to 0.06 its crap. But the model prints fine on the raft. They need to set the raft to permanently be at 0.1 to avoid this retarded issue which just lead to the filament getting worn out from the printer doing its retarded nozzle retraction thing that wears it away to the point of you having to pull it out and start over. This is my only gripe with tthe ultimaker, other than that its easily the best one out here.

I then started printing my models with no raft but they became so stuck i ended up pulling a layer of glass off one i had trouble removing. Never again. You need the raft if you cover a lot of surface area. Its a fake block alot of the time, epecially with the raft. I always let it mess up on the raft as i know the model. will be perfect.

To clean my nozzle i just heat it up to 260 jam in some filament and then ramp the temp to 0 whilst still pushing through the filament till the temp stops melting it. Then i wait till its around 60-70 or even 80 and whip it out gently (you dont want to bend the bars). Generally works everytime and i dont need to do the whole change material nonsense that way. The key is not letting the nozzle safety feature kick in for too long or else it will grind through the plastic leaving you to remove it as it cant pull it through anymore cos its been grinding away. This mechanism needs to be changed it ruins the experience and makes me want to pick up the printer and smash it into pieces everytime i hear that duk duk noise. Claiming to have a blocked nozzle.

Please ultimaker either make the grips larger or more spread apart. Or something as right now it just eats into the filament so much during retraction it cant grip it anymore and needs maintenance. After a few times this gets extremely annoying. Id like a setting that says ignore the nozzle block please and print regardless.

[swordriff 119]

Also I noticed that as I push the ABS past the teflon insulator there is a slight bit of resistance at the base of it, where the teflon part terminates into the melt chamber, is there supposed to be any resistance there or should it be completely smooth? I've heard plenty about deformed teflon pieces causing problems, but I've only had the printer since late Dec and haven't printed that much yet, but again this was after a ~30hr ABS print.

 

Yes. printing ABS 260+ over time deforms the teflon piece. When you take it out you will see it has

an inner wall collapse.. You COULD try reaping it a bit, even cut 0.5mm. cut must be straight,

surface flat.. (really!!)..

 

[cloakfiend 995]

I do 40hrs plus prints at 230 no problem but dont like those high temps. I stay well away from abs now. And when you manually push stuff in there is a bit of resistance getting into th head, dont be too rough. Its not that bad.

[ccw1984 1]

... lead to the filament getting worn out from the printer doing its nozzle retraction thing that wears it away to the point of you having to pull it out and start over. This is my only gripe with tthe ultimaker, other than that its easily the best one out here.

 

If you haven't already done so you should print IRobertI's improved feeder, or one similar. After installing it I haven't any any more issues with worn filament.

 

[ccw1984 1]

So I pulled apart the print head this weekend, and as I feared...

 

 

That 30 hr ABS print did some damage to the PTFE coupler, the inner edge was pushed out and burnt, and inside there is a depression with red PLA still in it. What I imagine is happening is that at that point the PLA is warm enough to be soft and as the filament is passing through if any rough edge (from the knurled feeder) catches in that depression the force is enough to 'skip' the feeder.

EldRick and I actually had the same idea (aside: I've purchased a Flex3Drive from him, so I'll be over on this thread soon), I ran a 1/8" drill bit through the end with the damage to remove the deformed PTFE, reassembled the print head annnd...it still under-extruded. Long story short I had to go up to a 5/32" to ream out the interior edge and "remove" the depression. I tried to make it a smooth transition from the original inner diameter (ID) to the new ID but I could only do so much with a drill bit and a round needle file. I've contacted fbrc8 about a replacement part.

(Another aside: I purchased the UM2 in December from MakerShed which led me to believe I would be getting one with the newer glass-impregnated PTFE part, however I believe I must have gotten one that had been there for a while since it had an older feeder and (obviously) an older PTFE part.)

So far it's doing MUCH better, but still clicking every now and then.

 

 

[mohissa 0]

 

(Another aside: I purchased the UM2 in December from MakerShed which led me to believe I would be getting one with the newer glass-impregnated PTFE part, however I believe I must have gotten one that had been there for a while since it had an older feeder and (obviously) an older PTFE part.) /quote]

Just a quick question. I just got my UM2 2 days ago from Dynamism. How can I tell if I got the latest version or not?

Thanks!

[swordriff 119]

Dear Mohissa!

I am sure they will send you a new version when you ask.

Personally, and many with me, prefer the old one, it is much more slippery,

letting the plastic move more easily!

Also I am not sure if the "glass impregnation" helps longevity.

[ccw1984 1]

Dear Mohissa!

I am sure they will send you a new version when you ask.

 

A whole new UM2? How do I get in on that!?

I've contacted support@fbrc8 about getting a new teflon spacer (on Feb 5) but have yet to hear back.

 

Personally, and many with me, prefer the old one, it is much more slippery,

letting the plastic move more easily!

Also I am not sure if the "glass impregnation" helps longevity.

 

I've been pouring over the forums, especially the thread on replacements/improvements for the coupler, the results with a vespel washer between the brass hot end and the PTFE look promising, I'd love to get my hands on one. Or something, anything that will last longer and let me print in ABS and PLA without having to worry about part failure.

The glass impregnation should give the part more structural rigidity, so even if it has the same thermal properties, it should be less likely to develop the ring indentation that so many see when the part fails.

 

[swordriff 119]

They will send you a new TEFLON coupler, not an UM2, Id be surprised!

I am bringing out a washer which is even more strong than a vespel made one.

Within weeks.

We have printed 300 hours ABS at 260 so far and Teflon looks like new.

Problem is that the material costs close to 1.500€ / metre, and you lose som when

cutting it and it is difficult to cut it straight.

Thanks.

 

[ccw1984 1]

Well, good news everyone! Fbrc8 is sending me a new PTFE coupler, should be shipping today. I'm also going to be implementing the improvement that EldRick suggested in his thread here:

http://umforum.ultimaker.com/index.php?/topic/6084-um2-bowden-block-cooling-improvement/

Adding a small diverter to increase airflow over the coupler to help keep it cool.

Also if I can keep the printer going until the new coupler gets here I'll be printing the parts for the Flex3Drive I've gotten, check out the thread here

http://umforum.ultimaker.com/index.php?/topic/6987-flexible-shaft-the-best-of-both-worlds/

I'd also love to get an improvement to the coupler and heater blocks so I'll be much more involved in the following threads:

http://umforum.ultimaker.com/index.php?/topic/7024-teflon-spacer-replacement/

http://umforum.ultimaker.com/index.php?/topic/7689-custom-heater-block-to-fit-e3d-nozzle-on-ultimaker-2/page-12

I don't recall seeing one, but I think a good stickied/pinned post would be a list of suggested 'Print Me First' improvements that most if not all UM2 owners should consider printing when they get their machines, things like the improved feeder by IRobertI and a lower friction spool holder. Those seem to be the most frequent and recommended suggestions to the 'help me with underextrusion/bad print/clicking' posts. Plus it's just such a cool feeling to say "I've printed an upgrade to my printer with my printer!"

Edit: I wound up doing this.

 

 

[ccw1984 1]

So the new PTFE coupler has arrived and in the interest of science I've atomic pulled the old one out and cut it in half to see what was going on.

 

 

 

So interestingly enough, it looks like I did have the glass-filled PTFE coupler (fbrc8 looked up the SN and it was in the 'newer' category) and it looks like that glass filling might be what the odd "feathering" around the bottom hole is.

 

 

 

 

 

After cutting in half you can see how a plug of PLA has formed where I had to ream out the previous indention. Also how a new indention is already forming in nearly the same spot. This leads me to think that the temperature and pressure at the PTFE/brass connection is high enough to deform the PTFE coupler even at the standard 210C PLA temperature.

 

However the temperature in that zone does not get high enough to make PLA reach a pliable state because once that plug had formed even heating the head to 240-250 couldn't get it out, forwards or backwards.

 

 

 

PTFE cut in half without the filament, had a hard time photographing this one.

 

 

 

Also had a hard time taking pictures of the PTFE/brass junction, but there is clearly a ring of burnt material where the two meet.

I'm wondering if it's better to clean this off so there is a nice clean seal between the two parts, or if it's better to leave it there as it may have some slight insulating properties since it's already been exposed to the heat and carbonized. Thoughts?

 

[bertho 6]

They will send you a new TEFLON coupler, not an UM2, Id be surprised!

I am bringing out a washer which is even more strong than a vespel made one.

Within weeks.

We have printed 300 hours ABS at 260 so far and Teflon looks like new.

Problem is that the material costs close to 1.500€ / metre, and you lose som when

cutting it and it is difficult to cut it straight.

Thanks.

 

If you do not mind, what material are you referring to?

I have a very customized UM-0 and might have to do a custom part for myself.

 

[ccw1984 1]

If you do not mind, what material are you referring to?

I have a very customized UM-0 and might have to do a custom part for myself.

 

There are several new materials we have found that may work such as Vespel and Tecasint.

Check out the following thread:

http://umforum.ultimaker.com/index.php?/topic/7024-teflon-spacer-replacement