1. Consider the detail level of your application.
Are you aiming to build very detailed or very large parts?
What is the minimum feature’s dimension required?
Nozzle sizes usually refer to the diameter of the nozzle orifice. Sizes from 0.1 to over 2.0mm are available from many manufacturers. The diameter of the orifice has a huge impact on the XY resolution and on the detail of the parts. For instance, a 0.4mm nozzle cannot build geometric features smaller than 0.4mm in the XY plane.
Hence the relevance of the nozzle size regarding level of detail.
2. Consider the part’s mechanical requirements
Is part strength important to your application?
Or rather its low weight?
It is proven that wall and extrusion thickness has a huge impact on the parts’ mechanical resistance to shock or compression. One can either make walls thicker by using more perimeters with a small nozzle at lower extrusion width, or by using less perimeters with a bigger nozzle at larger extrusion width. Due to the filament 3D printing process, consecutive perimeters are printed some time apart, and the cooling down of the previous deposited material will lower the quality of the bonding between them. For that reason, at a specific detail requirement, using bigger nozzles within those requirements and higher extrusion width will deliver stronger parts.
To build lighter parts on the other hand, thinner walls and lighter infill structures are desirable and enabled by “smaller” nozzles.
3. Consider the build speed requirements.
Is build time a relevant constraint to your application?
Or do you have all the time in the world?
Thicker nozzles will allow higher volumetric flow rates and for that reason a faster build speed.
It is important to remember that build speed is a volume related parameter, and only partially dependent on print speed. Meaning, it is possible to build faster at lower print speeds using wider extrusion width and height.
Let's evaluate a simplified example using a small 100cm^3 object and excluding geometrical impacts on time and speed.
Let's consider the hotend has a max volumetric flow rate of 20mm^3/s.
Consider also the layer thickness is 0.2mm and max viable print speed is 100mm/s.
Using a 0.6mm nozzle the required print speed to exploit the full hotend's melting capacity is 180mm/s.
At that speed the print would take about 1 hour and 23 minutes.
Because the speed limit is 100mm/s, the print would actually take 2 hours and 31 minutes.
Using a 1.2mm nozzle the required print speed to fully exploit the hotend capacity is 86mm/s.
And at this speed the print would be completed in 1 hour and 23 minutes.
We built faster at lower speed.
All values presented above are subject to approximation
4. Consider the hotend capacity.
Is your hotend capable of delivering enough Volumetric Flow?
As mentioned before, larger nozzle orifices allow more volumetric flow, but its orifice diameter isn’t the only limitation. In fact the limit of how much volumetric flow you can use is defined by the hotend capacity to melt the material.
As an example lets compare a 0.6 and a 1.2mm nozzle using a specific Max Volumetric Capacity.
Considering a 3D printer,
capable of delivering a good surface quality at up to 100mm/s,
with an hotend that can melt up to 20mm^3/s,
printing a part using 0.2mm layer thickness,
A 0.6 mm nozzle printing at 0.6mm extrusion width requires 11.14mm^3/s while printing at 100mm/s.
Inside the hotend capacity.
A 1.2 mm nozzle printing at 1.2mm extrusion width requires 23.14mm^3/s while printing at 100mm/s.
Outside the hotend capacity.
All values presented above are subject to approximation
At a standard or pre-defined print speed, the capacity of a nozzle to deliver material may be limited by the capacity of the hotend to melt it. For that reason some nozzles may not make sense for you, depending on what hotend you are using.
5. Consider the 3D printer’s kinematic capacity.
What is the top speed your printer can handle within your own quality parameters?
And what are your build speed requirements?
To maximize the build speed a calculation needs to be made to determine what are the nozzle sizes that can deliver the desired output just below the top speed threshold.
As an example, and using a simplification not dependent on geometry,
if a part has a volume of 500 cm^3,
and you want to print it in around 4 hours,
knowing your printer can print properly at speeds up to 200mm/s,
you need a 35 mm^3/s average Volumetric Flow Rate. (500 000 mm^3 / 14400 s)
Let's say your hotend can deal with so much flow.
For this specific Volumetric Flow Rate
and building using a 0.2mm layer thickness,
a 0.6mm nozzle would need 314 mm/s print speed average.
Outside the printers kinematic capacity.
a 1.2mm nozzle would need 151 mm/s print speed average.
Inside the printers kinematic capacity.
All values presented above are subject to approximation
For some applications there are nozzle sizes that have throughputs outside of your printer’s capacity to deliver good parts at a specific build speed. Those will be useless.
