ABS prints fine at first, then flow stalls

[jobjan 0]

Hi!

 

I'm printing ABS on an UMO+. At first printing works fine. It sticks to the bed, the flow is OK. When I push by hand it is not hard at all to extrude ABS.

 

But after the first few layers, extrusion starts sucking and the print fails. When I then manually push the ABS through the nozzle I have to push very hard. Also, the ABS that comes out looks more 'dull' and less molten.

 

If I then 'clean out' my nozzle with PLA (just push through at 230) and then re-load again with ABS, I can print fine for a few layers, but then it fails again.

 

I have no problems whatsoever printing PLA, PETG or TPE.

 

Any ideas on how to fix this?

 

Temperature: I tried 230-260

No fan

Bed: 105C

Speed: 10mm/s for first layer, 40mm for rest

Initial layer: 0,3mm

Other layers: 0,2mm

 

Edited January 14, 2020 by jobjan
Clarified title

[gr5 2,167]

It's probably over cooking in the nozzle.  You can fix this by printing cooler or faster.  Do .3mm for bottom layer (default I think) and 0.2mm for remaining layers.  Until you've experimented more.  You can certainly do 0.1mm if you stay at 40mm/sec and your nozzle is cool enough.

 

So what temp is best?  I'm really not sure.  I think you want to stay between 240 and 245C but start out at 230C as an experiment.

 

So for now, try 0.2 layer height and also do 20mm/sec print speed on that bottom layer to keep the plastic flowing.

 

That's clogging.

 

Other problems you will have is layer adhesion and parts sticking to the bed.  You really want the bed at 105C minimum, 110C recommended for the ABS to stick extra well to the bed but I don't think you can get it up to that temp without enclosing the printer - as a minimum enclose the 3 open sides and throw a big box over the top.  Let the air get up to 35C (servos will be fine even at 40C air temp).

 

This higher air temp will help with layer adhesion.  Also lower the fan a lot - print at what sounds like 1/4 power (around 30% I think).  If fan is too low then overhangs will look bad.  If fan is too high then part will seem fine until you break it and you will realize it breaks along layer lines which means you didn't have good layer adhesion.  It should break in a way completely (or mostly) ignoring layer lines.

 

[jobjan 0]

Thanks for your advice..

 

I've tried 20mm/s for the bottom layer, 40mm/s for the rest

and 0,3mm layer height for 1st, 0,2mm for rest

at both 230 and 240C

 

but the same thing happened, it stops at a few layers. Interesting is that all prints stop at more or less the same point. See pic:

 

Any more suggestions?

 

I have no problems with layer adhesion (for the first print after re-loading)

[jobjan 0]

 

I've not been able to successfully print ABS yet. I'm starting to get frustrated 😞

 

So far I've tried:

230, 240, 250, 260 C

 

First layer at 10 mm/s, 20 mm/s

Other layers at 20 mm/s, 40 mm/s or 60 mm/s

 

Layer flow at 100%, 130%, 150%.

 

And combinations of those.

 

Bed temperature: 105C

 

First layer 0,3mm, next layers 0,2

 

No luck yet. At first the print starts fine, the print sticks to the bed, but then after a while it fails (the flow of ABS deteriorates).

 

Any ideas on how to fix? Thanks in advance!

Edited January 16, 2020 by jobjan

[geert_2 557]

I don't have much experience with it, but ABS is said to decompose fast in the nozzle, if sitting there for too long (=or too hot, or printing too slow), causing clogs.

 

If that is not the case for you, then have you checked that the little fan for cooling the nozzle is working well? On an UM2 this is sitting behind the nozzle, invisible from the front. I don't know where it is on an UMO. This could suck-in hairs and debris, and get stuck.

 

Also on an UM2, a severely worn out white teflon coupler could cause underextrusion after a while. I don't know if an UMO has something similar?

 

The white filament-end after a cold pull on an UM2 shows a thickening where the teflon coupler is worn out. But I have seen even worse. This hinders the material flow.

 

Not sure if any of these could be the cause for you, but it might be worth checking?

 

[jobjan 0]

Thanks a lot Geert,

 

There is no extruder cooling fan on the UMO. As far as I know,

 

But your other suggestion might point in the right direction, because my cold pulls don't look close to your images ar all...

My teflon coupler is quite new, but might there be something wrong lower in the hot end? Any idea where?

 

 

[e23 1]

Ultimaker 3 - ABS (I have to use the plastic cage you get on the side or else the ABS will warp).

 

Printing Temp: 225 C

Build Plate Temp: 80 C

Print Speed: 75 mm/s

Fan Speed: 2%

Layer Height: 0.1 mm

Infill: 100%

 

Brim and Z Hop when retacted

 

Use the glue stick to as well that came with mine (very thin even layer).

 

---

 

Maybe this will help. IDK if it will for you, but maybe it will help.

 

I print all the time and this works perfectly (basically perfect) for me.

 

---

 

ABS is not easy to print to as well. I've had problems with ABS myself. It's not just plug in the USB for the most part like PLA and you are ready to go.

 

---

 

Side note: switching to PC after this due to the dangers of ABS (mostly well ventilated area though) for now.

Edited January 19, 2020 by e23

[gr5 2,167]

Try 25mm/sec on first layer and 40mm/sec on the rest.  Try coolest temp (230C).

 

Yes, the UMO doesn't have that fan blowing on the teflon and the fan fixed an issue that looks like this where it prints fine for a few layers but if there's too many retractions the heat slides up and causes clogs in the teflon area or just above.

 

I'd probably replace the teflon part.

 

Also check the diameter of the filament.  sometimes a 3mm filament really is 3.00mm (very very rare) and that can get stuck in the bowden.  You'd probably notice though when you tried to slide the filament out a bit as part of some test.

 

I'm a bit stumped however.

 

Oh wait - it could be the extruder driver chip is overheating.  If so it would sound a little different where the extruder turns off for a portion of a second and then quickly turns back on again.  The fix for this issue is usually to *lower* the extruder current to around 900ma.

 

[jobjan 0]

Thanks both e23 and gr5 for your suggestions, much appreciated..! I've tried most of them now.

 

Speed settings: With 25mm/s on 230 the first layer doesn't stick, so I've tried 10mm/s on 230. But same result

Lack of a fan on the UMO: I've tried printing without retraction (this should make a bit of a difference, right?), no luck

Filament diameter: Measured, it's 2,85mm

Extruder driver chip overheating: haven't heard the sound you're describing and I don't know how to lower the extruder current... Is there a noob way to test if this is happening?

Replacing teflon part: I've taken the hot end apart, and to me (but as said, I'm a noob), it doesn't look as worn as some other images I've seen out there. What is your expert opinion? Should this part be replaced?

[geert_2 557]

If this teflon coupler was on my UM2, I would replace it, if I had printing problems. There seems to be an indent inside the tube, close to the bottom, and the inner diameter seems to have gotten oval instead of round? But this is hard to see for sure on photo, as there could be weird light-effects too.

 

Concerning bonding, I think gr5's method with dilluted white wood glue should also work well. At least it did work well when I tried it for PET some years ago. But my "salt method" will *not* work for ABS.