3D printer nozzle diameter comparison: 0.4mm vs. 0.35mm vs. many others

Owning 3D printers with different nozzle diameters, I am able to give some first-hand experience on their advantage and disadvantage. Hope these could be helpful. FYI, my 0.4mm printer nozzle is from Up!3D, and the 0.35mm is Type A Machine. Basically, nozzle of bigger diameter extrudes thicker strings, and vice versa. This is usually the first impression. Different diameters, however, do produce different issues, here are the details:

1. Things that don’t really matter:
   • Filament material/size:
     You can buy any type of filament from the market as long as the machine takes. The nozzle diameter has nothing to do with the filament size. The most available type is the 1.75mm diameter filament, and that’s what I go with. Both ABS or PLA work with no regard to the nozzle size.
   • Machine structure:
     The nozzle diameter won’t impact the mechanical design of the system. Most RepRap systems are installed with a X-Y-Z 3 degree-of-freedom linear moving module, on top of which mounts the heating nozzle to melt and extrude the material. If you can find a compatible replacement nozzle with different diameter, I believe you can simply swap it and the printer still works.
   • Software:
     Same software will work for different nozzle diameters. However, you do need to change some parameters to make it work properly. For example, since bigger diameter extrudes out thicker strings, you need to leave a bigger setting for each layer.
2. Bigger nozzle diameter is better for:
   • Faster printing:
     This is easily understandable as bigger nozzle producing thicker strings reduces the number of layers you need to print. The nozzle travels less and saves time!
   • Better grabbing / sticking to the printer’s bed:
     This is an interesting phenomenon I discovered after using both of my printers. A nozzle with smaller diameter produce thinner strings which cools and solidifies really quick right after they left the nozzle, which is hot. As you know, the plastics becomes less sticky when it cools down. The filament extruded from a bigger nozzle, however, retains its temperature longer that is enough for the filament to settle on the build plate.
   • Support-less prints:
     This interesting effect is actually caused by the same reason above. This time it is not about sticking to the bed, but to the layer just print. Melton plastics sticks easily onto its lower layers even it is hanging out a little bit with some offsets. This, for sure, will help eliminate the supportive structure if the print itself can hold well. On the contrary, quickly solidified plastics from a smaller nozzle is less likely to achieve this, or at least, the amount of distance that a new layer can hang out is much more limited, in which case will require printing supportive structures.
   • Better reliability:
     This is from the statistic point of view, the machine that finishes the job faster is sure to have less chance of failure, assuming both have same success/fail ratio. In general, RepRap type 3D printers don’t have really high reliability simply because of the way they are constructed: open-loop. The motor may slip a tooth if anything happens to be in the way, and open-loop control won’t be able to detect that.
3. Smaller nozzle diameter is better for:
   • Smoother finish：
     I believe the following picture will explain everything!
   • More rigid prints:
     When I drill a hole on the print, I feel more like drilling through a piece of tofu if it is printed with bigger nozzle diameter. And it is more flexible than smaller nozzle. I think this is cause by its inner netting structure. Smaller nozzle ends up more layers and causes the binding more stronger than the bigger nozzle, which has fewer layers.
4. Both sucks on：
   • Accuracy:
     You should never rely on any of the RepRap type 3D printers for accurate prints. The system can control the nozzle position accurately, but has no control where the extruded filament should stay as soon as it leaves the nozzle, not to mention the plastics shrinks after it cools down.

My rules of thumb to choose which printer to use for a certain job is:

• If I desperately need this part in a hurry, I use the bigger nozzle.
• If I care most for this smooth surface, I use the smaller nozzle.
• If I have to leave a job overnight, and don’t want to have a fail part on the next morning, I use the bigger nozzle.
• If I have many important and fine details on a part, I use the smaller nozzle.