7.3. Selecting nozzle sizes for large prints

Printing large parts is a different kind of challenge for 3D printing. Rather than worrying about sub-millimeter accuracy and finish, we focus on moving the maximum amount of filament in the shortest time possible. Plonking a big fat nozzle makes a big difference on print times, but in order to maximize output, we need to understand the factors that impact print times

Note

These notes are based on my experiences with the Prusa i3 Mk3 and Artillery/Evnovo Sidewinder X1 printers. If you are using a different printer, please verify the hardware details are similar.

To fully optimize printing large parts, it’s important to determine your extruder’s maximum volumetric rate. Mount your preferred nozzle and filament, then run the tests noted on the linked calibration page.

7.3.1. Right-sizing nozzle sizes for large prints

3D printing is a complex topic, and there are few magical fixes for common problems. This includes selecting an appropriate nozzle size. Larger is not always better, and you want to consider the implications of using larger nozzles.

7.3.1.1. Print detail

When 3D printing, there are two planes of detail we need to consider:

Horizontal detail in the XY plane. These are the tops of surfaces or small details that protrude. Although you can print some parts smaller than your nozzle size, most slicers will simply not generate extrusions much smaller than the nozzle. Thin walls can be printed, but tend to be weak. Corners will be softer as nozzle size increases.
Vertical detail in the Z plane. Thicker nozzles can still print thin layers. Generally, you’ll have the easiest time printing heights over 25% of the nozzle size, but nothing says you can’t try to go lower. A larger nozzle can still produce good vertical detail.

7.3.1.2. Part strength

Stefan of CNC Kitchen has done some interesting tests on part strength. Over several videos, he has demonstrated that:

Print strength comes primarily from perimeter thickness, not infill density. Thicker walls provide considerably more strength.
Lower layer heights produce stronger inter-layer adhesion. If your parts will be pulled apart along the Z axis (height), thinner layers will hold together better. While Stefan has thus far only tested with a 0.40mm nozzle, I believe it is the ratio of layer height to extrusion width that counts. The lower the height compared to width, the more oblong or “stadium shaped” the extrusion and the more surface area that touches between layers. You can print with greater layer heights so long as the height-to-width ratio is maintained. A larger nozzle increases the optimal range.

7.3.1.3. Speed

A large nozzle can push out just as much filament at a lower speed as a smaller nozzle moving at much faster speeds. In fact, since the larger nozzle comes up to speed more quickly, it will push more filament in a given period of time under the right conditions. However, speed is an illusion. The big gain from using large nozzles comes from eliminating perimeters. Using a large nozzle with wider extrusions may allow us to print the same wall thickness with a lower perimeter count.

Ultimaker Cura allows specifying wall width instead of perimeter count. That slicer will calculate the number of extrusions required to achieve the desired with. When using PrusaSlicer, you will have to calculate and set the number of required perimeters under Print Settings.

Note

PrusaSlicer has recently implemented a top and bottom layer minimum thickness setting. Future releases may extend this to wall thickness.

7.3.1.4. Infill optimization

While infill doesn’t add as much strength as perimeters, we do want infill to provide some structural reinforcement with large hollow prints. Here again, a larger nozzle will produce wider infill extrusions, thus greatly reducing the number of moves required to print an equivalent amount of infill.

Todo

Add more detail and example prints.
Add table of safe speeds for different nozzle sizes.

7.3.2. Conclusions

Larger nozzles require much slower linear speeds than can be used with smaller nozzles. PrusaSlicer will do the necessary adjustments if Maximum Volumetric Speed is set correctly.
Larger nozzles can significantly reduce print times provided you can eliminate the need to print a perimeter.
You will need to calculate the number of perimeters required for a desired wall thickness when using PrusaSlicer.