The new PLA Silk+ filament from bambulab comes with a warning, recommending not to use the 0.6mm or 0.8mm nozzles
Not Recommended: Hotend with Hardened Steel Nozzle 0.6 mm / 0.8 mm
Why?
If you look closely at Silk poop, youāll notice that it comes out looking like a cheese doodle or Cheesy Puffs if youāre in the UK. The filament actually expands like a cheese doodle upon exiting the nozzle. I would believe that if Bambu is not recommending it on this size nozzle it may be due to the fact the filament would not extrude well due to this expansion issue.
But in all fairness, what do you have to lose? Try it. If you go that route, please share with us your experience.
1 Like
The issue is not just for silk.
Comes down to how much time a filament might have to spend inside the melting chamber and how badly it reacts to pressure and heat.
Silk filament is a complex blend of plastics, fillers and additives.
With the right temp and speed it comes out wonderfullyā¦
But as Olias already pointed out - the devil is in the detailā¦
I learned the lesson the hard way when I tried to print a sample of foaming PLA using the 0.6mm nozzle I had in at the time.
Came with quite specific print temp, speed and flow ration stated on the bag - so what could possibly go wrongā¦
Everything - literallyā¦
Started just fine although it really expanded like a marshmallow in a vacuum chamber once out of the nozzleā¦
Looked good, so went to buy some snacks.
Came back to a disaster.
It literally started to spit the filament out and this must have started in those areas where the print had to slow down a lot for overhangsā¦
Foaming PLA is nice to work with once printed, not so much though when you have to chisel out your print head ROFL
Was a long and frustrating Satdayā¦
Iām aware that PLA Silk has challenges printing with a wider nozzle.
-
Starting with retraction, the stock 0.6mm nozzle profile comes with 1.2mm retraction length. This causes air bubbles to be trapped and explode like if the filament is wet (even if itās not). I believe this is partly because of the goopy filament consistency.
- too much retraction and you get holes, too little and you get strings
- too much retraction and you get holes, too little and you get strings
-
Then with the way it swells (like you said), the nozzle drags the lower layers as itās coming through, and it exacerbates the effects of vibrations. This causes ringing diagonally rather than vertically.
But, is that why? I wish they documented why >_< that way Iād know what to expect.
2 Likes
I think it all comes down down to what you could call flow dynamic of the EXTRUDED filament.
Take plain PLA, calibrate it properly and see how fast you print simple things with it until it goes bad.
You will find that once reached the limit an increase in nozzle temp still lets you push a bit further.
Now try the same with a model that has some sharp corners, like a star shaped ornament.
Suddenly all hell breaks loose as we now have to deal with speeding up, slowing down, pressure changes and constantly changing flow rates for those corners and straight moves.
Silk and other complicated filaments usually donāt behave in a linear fashion like plain PLA would.
It is not so much the unavoidable moisture in the filament that makes silk so bad, it is volatile compounds that make it so silky.
Same way your jerry can expands when you leave it in the sun the filament will (or would) in the melting chamber.
There is only one way out though - through the nozzle.
Pressure changes in the melting chamber make a mess out of the fluid dynamics involved here.
And as you said, retractions only make things worse.
Thatās because it allows those volatile compounds to turn into vapour, then the deretraction comes, compresses it all and you get way more pressure than before.
Resulting in those ripples and other unwanted problems.
And imperfection on one layer transfers onto the next and then you end with corrugations like on a dirt road.
You would require a rather huge melting chamber to print such filament in a big nozzle but that would come with the problem of getting the silk effect to work as the time the filament spends inside the melting chamber affect thisā¦
A no win situation really, stick with what works and accept that the print take a lot longer - you do get a slightly better look though.
1 Like
I like your explanation, although I disagree with the idea of ājust stick with what worksā as a way to say ādonāt ask questionsā 
Not at all 
Stick with what works simply means that sometimes there is no possible, let alone easy way to do certain things with out printers.
Only by asking and questioning things we can learn and improve.
I also sure that it would be possible to print silk with a 0.6 or even 0.8 nozzle just not if it is would be worth the time and wasted filament trying to calibrate things.
We donāt print filled filaments with 0.2mm nozzles because it makes problems we can related to.
For silk or other expanding filaments it is a whole new can of worms.
Not to mention that even if you make it work you still might find that the physical properties of the filament got ruined.
The balance act with silk is hard enough as it is and I guess thatās the main reason Bambu and other filament providers advise against using larger than 0.4 nozzles.
1 Like
Iām not surprised. Iāve just had to switch a project to .4mm from .8mm cause āsilk plaā is not very happy with the larger nozzle. Lots of stringing and suchlike.