Small nozzle printing best practises

Hi,

I recently bough a .25 and a .15 nozzle for some jewelry prints. I have a bondtec extruder so I didnt have any big issues with the .25 nozzle. I dropped the speed down to 30mms and got some decent prints out.

However with the .15 I noticed two things:
First the cooling. The heat really concentrates in small models and I have to have at least to models on the bed at the same time so allow some time and airflow but that is doable even though annoying.

Second underextrusion. In general I get good flow and im only printing at 20mms and I even disabled retractions, but I still get some clearly underextruded parts. I can see no leakage on my extruder and as far as I can tell not skipped steps.
I dont know if im printing too fast but the speed doesnt seem excessive.

Anyone want to share some experiences? Ill appreciate all pointers.

Cheers

I have also noticed heat build up in small objects. It's very hard to get rid of, but a well ducted fan is your best bet. I've recently had to fine-tune my cooling for some baubles that I print in vase mode, and my ducts have dealt with them very well. I have noticed wide ducts do better then narrow, and they want to be well directed at the top of the nozzle (or just before the nozzle) to really optimise cooling.

As for the under extrusion, perhaps a little bit of extra extrusion after retraction will help the issue? Just a really small amount to re-prime the nozzle. What happens if you turn retraction off?

Do you have a direct drive extruder or geared one? Printing with small nozzle and low E-steps/mm can get ugly.

Many underestimate how much smaller the amount of material is that you can push through such a small nozzle per second.
Going from a .25mm Nozzle (0,05mm²) to a .15 (0.018mm²) is a factor of 2.8, so be prepared to drop the speed not by 50%, as you did, but by at least 70% or even more.

---

[www.bonkers.de]
[merlin-hotend.de]
[www.hackerspace-ffm.de]

Retraction: I turned it on again to 0.5mm and at least with PLA that's really necessary because any amount of stringing will kill the model because its impossible to remove. Reprimeing i will test though.

Cooling: I have a good 360 cooling duct and i cranked it up to 80% which makes it better. The "two models 5cm apart method" seems to work best so far.

Extruder: Yes, i use a bondtec with 5:1 gearing and really short bowden, but I increased over extrusion to 105% that seems like a good idea in general.

Speed: Good point. I don't have a micro scale to test filament grinding/slipping, that would actually help here because one wouldn't here any grinding even if it happened.

BUT (big but^^) i noticed something else that had a much bigger effect and that is layer height. I had tested as low as possible and ended at 0.05 which is a bit too much in think. When I went up to 0.075 quality became much better. Its just a bit more volume and that probably smooths out a lot of issues.

Also with any layer heights below 0.075 i have the feeling that the x/y error/jitters are more visible that the layer lines, so decreasing layer height wont do much more for quality I think.