6.4. Maximizing output part 2: infill settings

Maximizing output requires more than just setting faster print speeds in your slicer. These notes show how slicer infill settings can be optimized to reduce 3D print times.

Partway through a lengthy thread on the Prusa forums on how to optimize print times for large, functional prints, @jsw mentioned printing a large cube sized to completely fill the Mk3 bed. This got me thinking about the importance of infill and how the selection of infill patterns can affect overall 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.

6.4.1. The challenge

The challenge this time was to create a small cube in PrusaSlicer, then resize it to the maximum build area. This resulted in a 209.92mm^3 cube ready for slicing. Unlike our previous example, this print has a cavernous internal area. Due to the large supported top, infill is required. Using a standard 0.4mm nozzle with 0.15mm layer heights, generic PLA, the print is estimated to take 5d2h17m (7,337m).

6.4.2. Selecting the right infill pattern

The PrusaSlicer has implemented some impressive features with the release of v2.3.0, including expanding the range of infill patterns. Until recently, infill patterns available in PrusaSlicer provided a pattern with a consistent density throughout the print. It was possible to use modifiers to change settings in specific parts of a print, but this was a manual process and could be quite time consuming. With v2.3.0, Prusa’s team has slipped in some truly amazing adaptive patterns ideally suited to our challenge.

6.4.2.1. Support cubic

The first variation I tested was the Support Cubic pattern. This pattern prints a range of triangular lines horizontally across the infill area, much like the previous Stars and Triangle pattern. Where it gets interesting is that this pattern is automatically adjusted to provide higher density at higher layers, making it ideal for our print challenge.

Here’s a picture of the 1st layers of our test print using the Support Cubic infill pattern:

Fig. 6.39 Support cubic infill bottom layers

Things get magical as you move to the top layers:

Fig. 6.40 Support cubic infill top layers

A few observations:

Switching from the default Gyroid infill pattern to Support Cubic dropped the print time to 16h1m (961m).
Switching to a 0.6mm nozzle profile with PETG and tweaked print settings bumped the time back to 17h18m (1,038m)
Enabling variable layer height on the cube with the same settings dropped the time estimate to 9h41m (581m).

By selecting an optimal infill pattern along with adjusted print, filament, and printer settings, we’ve dropped print times down to 7% of the original estimate, a 12X time savings.

6.4.2.2. Adaptive cubic

The Support Cubic infill pattern optimizes support density for top surfaces, but Prusa has also provided an option to provide all-around support with optimized infill density. The Adaptive Cubic option applies a similar infill pattern, but providing increased support along all horizontal and vertical surfaces. This provides improved part strength without excessive infill.

Here’s a cutaway view of the same print using Adaptive Cubic infill:

Fig. 6.41 Adaptive cubic infill print center

6.4.3. Other infill optimizations

PrusaSlicer supports other infill optmizations:

Enable Combine infill every X layers to have infill layers be combined into a single pass. You still need to be cautious of the impact of layer heights on infill strength, but this can be particularly useful if you’re printing low layer heights with a large nozzle. 2 or more infill layers can be combined into a single physical movement.
Enable Only infill where needed restricts infill to only those areas where higher layers require support. This is essentially an “internal support” option that avoids generating infill where it’s not needed. Note that this will significantly reduce the strength of the printed part if you are depending on support for rigidity. This option is well suited for cosmetic prints.

6.4.4. Extrusion widths

Another technique you can try is adjusting the extrusion width used for infill. Wider extrusions result in fewer, wider infill lines that are faster to print, but don’t provide as much support for top surfaces. I found that using the same very wide extrusion widths that I used for perimeters resulted in insufficient infill density for roof support. I wound up setting a thinner extrusion width (100% of nozzle size) for infill. This is contrary to the usual advice to use wider extrusions for strength, but since I’m relying on perimeters for strength, it seems a reasonable trade-off. This is definitely a trade-off and is something you’ll need to experiment with.

6.4.5. Balancing infill and perimeter quality

Finding the right settings to optimize production while maintaining quality is an ongoing challenge. This time, I sliced the cube with my optimized 0.6mm nozzle settings, but wanted to show how one can maintain exterior quality while still reducing print times. I tweaked my settings as follows:

Set Maximum layer height for my extruder (nozzle) settings to 0.24mm.
Applied VLH (all layers set to 0.24mm).
Set infill to Combine infill every 2 layers. At 0.24mm layer height, 2 layers will result in an extrusion height of 0.48mm, ideal to stay at or below 80% of nozzle size.

With these settings, the estimated print time is 13h13m (793m), a marked improvement over the original 5d2h17m (7337m). The pic below illustrates the 0.24mm wall layer heights with 0.48mm infill layer heights:

Here’s the resulting print showing the varying layer heights used on infill and external perimeters: