0.25 mm nozzle extrusion problems / pressure build-up

[bot]

Hi everyone. I've printed before with .25 mm nozzles routinely, and didn't seem to be having the problems I am having now. It could be that the models I printed before didn't have so much retraction in them, due to geometry, but this seems to be only happening lately, which is what's very frustrating.

I have an e3d v6, fed from an eZstruder through like a 1 m bowden tube. The nozzle will appear to begin working fine. The print starts well, la de da. Eventually the nozzle will get a partial clog and then a RUSH of pressure, spewing molten plastic everywhere. The pattern is like: Extrude fine, retract retract retract, inconsistent extrusion, splooge, extrude fine.

I've tried all sorts of varying retraction settings, to varying degrees of success. I can't seem to find the right balance.

I'm using Simplify3D. Base settings are like so:

Retract length: 1.5-3.8 mm (3.0 usually)
Retreact speed: 25-100 mm/s (used to run 50, then 100, then 25 more recently)
Coast: 0.5-2 mm (usually run about 1.5)
Wipe setting: 0-2mm (usually run about 0.5-0.75mm)

I'm starting to think it's the fact that I recently lowered my retraction speeds. This provides much better retractions. Perhaps, before, my retractions weren't really effective (it WAS string city) and thus allowing the nozzle to not partially clog.

I would appreciate anybody's input, or any settings they are using with a 0.25mm nozzle.

Thanks!

[626Pilot]

I used to, long ago. Slow speed and higher (sometimes significantly higher) temps helped. If the filament is translucent, the added crud might be messing you up. Try 2-2.5mm retracts @ 15-25mm/sec. Do you have a geared extruder on that machine? Tried canola oil?

I used a 0.35 nozzle when I had a Budaschnozzle and it allowed a surprisingly good increase in fine details over 0.4, not too much backpressure either. Unfortunately, the Buda was a crap hot end that would get heat soaked even with a cooling fan. Prints that lasted over 20 minutes would usually fail.

[bot]

I do have a 5:1 geared nema 17. I'll try just playing around more with the retracts. It just gets frustrating doing so many prints trying so many settings. I don't really want to try canola oil.

[mhackney]

.25 mm nozzles require near perfection. Your symptoms sound like what I call hydraulic plugging. Looking at your settings I think your retract is too high. I rarely go above 1.5mm with a .4mm nozzle. With a nozzle this small you really only need enough retract to relieve back pressure. I'd try 1mm and slow - 20 mm. Coast and wipe are not going to materially affect extrusion and I usually use .5mm coast and 1mm wipe with .25 to .4 mm nozzles. The other thing is, if you have areas where there are lots of rapid fire retracts, that can be a killer. I recall that S3D has a setting (KISS does) to prevent retracts if the extrusion is less than a set length. Change that to 4 or 5mm. Think about it - the perimeters are usually printed in a nice continuous extrusion with few if any sort segments and retracts. It's those pesky infills at corners, thin walls, etc that result in short extrusions requiring rapid retracts. But, these ultimately get hidden so a little drool or drip is not really going to hurt your print. And with such a small nozzle and reasonable print speeds, you'll move to the next segment before the retract would have occurred so the likelyhood of problems decreases.

It is also really important to have clean filament. Any dust or debris can and will clog that little nozzle. I'd put a cleaner in the infer path - a simple microfiber cloth wrapped around the filament would do it.

So to recap:
short retract: 1mm
slow retract/advance: 20 mm/s
long minimum length for before retract: 5mm
advice from me: priceless!

(sorry, I just had a glass of wine with dinner).

626Pilot, I love ya man but "canola oil"? Were you just poking me or do you use it?

The Taz 4 came with a Budashnozzle and .35mm nozzle. Convection cooled cold end was a kiss of death. A simple water jacket and it's now a great hot end. I still think a lot of issues could be eliminated with water cooling. I've just seen such great consistent results from my water cooled Kracken and E3D V5 and V6 extruders.

[mhackney]

Thank you for your last post bot! Canola oil spanola oil - yech!

[bot]

Thank you so much for the guiding advice. I'm about to do a test print now with settings not too far off what you said. But the next test will be with those exact recommended settings. Yech is right!

[mhackney]

Have you tried several different filaments also? I have a translucent smoke PLA that is beautiful and pretty easy to print but is brittle as all heck. Odd stuff. I wouldn't attempt to print it a .25mm

[bot]

Hmm the stuff I'm using is fairly brittle. I did have this problem with several filaments recently. I think the problem is that my retracts have been working, and I'm using a 1.8 mm ID bowden tube so the retracts are even less needed than on my rostock max. I did get it working well with next to no retract... but that was pretty gross to look at. It's a balancing act.

[mhackney]

Sometimes you can use a quick and long (~6mm) Z lift to snap the filament and prevent stringing. Lower the hot end temp in 3° increment until you get it right. I use this trick all the time.

How do you find the 1.8mm ID PTFE? Found any filament that won't go through? I've been considering trying some.

[bot]

I do find that some filament jams itself simply in the bowden tube. It can be quite annoying, but I seem to have found a supplier that never goes above 1.8mm too much (filaments.ca) I've put several kg of it through the machine in the past few weeks and none of it got caught up on the tube. I think it has "improved" retraction performance, but I still haven't got it all figured out. I was trying to keep slicing profiles the same between my rostock max and the new machine, but this bowden tube is almost twice the length but slightly smaller ID, so things are definitely different.

[626Pilot]

626Pilot, I love ya man but "canola oil"? Were you just poking me or do you use it?

Of course I do. It works great! Retraction and surface quality are both improved. Especially retraction. I have my bowden length down to about 100mm now, and it still helps. A few drops of the stuff into the top of the tube before a print is all it takes.

bot, maybe your filament needs to be dehydrated.

[bot]

There is no way I'm putting any oil into the bowden tube. MAYBE I would put it in the heatbreak... but I'm not going to unless I get desperate.

I think I'm going to try getting some 2.0 ID bowden Tube and trying it out. The 1.8 has significantly more friction than the 2.0. After this, I might put a nema11 extruder right on the effector, get rid of the large length of tube.

[bot]

So it seems that moving to a 2.0mm ID bowden tube actually improves the performance over the 1.8mm ID tube. If there is a benefit to be seen by the 1.8mm ID, it is not in long bowden tubes. Perhaps if the system is direct drive but requires a bit of ptfe tube, the 1.8mm might be a nicer choice... but I would highly recommend people avoid the 1.8mm ID tubes in long bowden systems.

[626Pilot]

It makes sense. PTFE is supposed to be low-friction, but it isn't exactly slippery. Filament will readily bind against it if the tube bends enough. I think those clips that keep the PTC fitting from bobbing up and down on retract are a better solution.

[Polygonhell]

1.8 is really tight for 1.75m filament, it's actually usually specced at 1.75 +/- 0.05 if it's decent filament, sometimes the tolerances aren't that right, and it will exceed 1.8mm. Taulman for example actually deliberately oversize their filament. So 2mm is about the right diameter for a Bowden tube.

For historic reasons, 3mm filament is actually not 3mm, rather it's designed to run through a 3mm orifice so it's usually 2.85 mm +/- the tolerance.

[bot]

Yup, totally. I just saw this tube available and thought "hey maybe that will help reduce bowden effects." I saw no reduction, at all, of the negative effects of a bowden system, and only added drawback. Just wanted to update everyone in the thread to not follow in the 1.8mm ID footsteps.

[nitewatchman]

Glad you posted, I was actually looing for the small bore tubing thinking, "This has gotta be better cuze it's hard to find."

[bot]

I'm glad I could help. Saving someone the wasted time is why I like updating threads. Just as a note, going to the 2.0mm tube from the 1.8mm alleviated all the problems I was having in this post. I can now print with the .25mm nozzle, at 50 mm/s running my usual retraction settings. Bad 1.8mm bowden tube, bad! I'm still going to try putting the nema11 and extruder right on the effector, but I'm in no hurry right now.

[Windshadow]

I wonder if you happen to get a batch of filament that mikes well under 1.75....

say 1.71 or less that having your chunk of 1.8 might let you use it rather than scrap it?

This is asked by a total noob with very very little knowledge of all this, it just seems that perhaps you might not want to throw it away

all together now..... the watch words of every tinker I have ever known

!! IT MIGHT COME IN HANDY SOMETIME !!

[nitewatchman]

I wonder if you happen to get a batch of filament that mikes well under 1.75....

say 1.71 or less that having your chunk of 1.8 might let you use it rather than scrap it?

This is asked by a total noob with very very little knowledge of all this, it just seems that perhaps you might not want to throw it away

all together now..... the watch words of every tinker I have ever known

!! IT MIGHT COME IN HANDY SOMETIME !!

I have a shop and two garages literally knee deep in stuff that might come in handy someday!

[bot]

Definitely, smaller filament works well with it. But as stated, filament tends to hover around 1.8 or above too often for this to be reliable. Also, I never saw any added benefit to the 1.8. Performance seemed the same as a 2.0mm one.

[Mac The Knife]

1.8 ID would be ideal for the folks printing with weed trimmer line.

[blackrabt]

The 2mm ID bowden tube sounds like a winner. I was having issues with my prints that turned out to be related to my retractions being too long/fast. It would actually back the bowden tube partially out of the hot end and then the filament would bunch up. I turned that down and the problem -seems- to have gone away but I think a switch might be nice to take some more stress off it.

Any word on the larger ID with flexible filaments? It seems like giving them too much wiggle room might lead to issues.

[bot]

I did print a semi-flexible TPU, which is much stiffer than ninjaflex, through the 2.0 without issue on my Rostock max. I doubt the added firction of the 1.8mm tube would have helped with the flexible filaments.

To remove the play in your bowden tube, you should wrap a solid-core wire or print a small plastic clip to sit under the press-fit collar. This holds the tube rigid in the "extended position" and makes retractions 1000% better.

[blackrabt]

I did print a semi-flexible TPU, which is much stiffer than ninjaflex, through the 2.0 without issue on my Rostock max. I doubt the added firction of the 1.8mm tube would have helped with the flexible filaments.

To remove the play in your bowden tube, you should wrap a solid-core wire or print a small plastic clip to sit under the press-fit collar. This holds the tube rigid in the "extended position" and makes retractions 1000% better.

Thats a great idea, thank you bot!