|The multi-compartment box|
as seen in Autodesk 123D
[update: if you want more info on this particular model - a Button Battery Box - see my newer post on that]
BackgroundThe "SHELL THICKNESS" setting in slicing software is used to define how many side-by-side solid lines of plastic will be used to line the walls of your model. With thin wall models - like a small box - the wall of the model, the Shell, defines how strong the box will be. So it is quite important. That setting also MUST be a multiplier of your printer's nozzle width. (according to in-app tips, help content and lore, which I now know is misleading).
|the box in CURA Layer view -|
notice the hollow walls.
The same should be true with thicker wall, which of course will be multipliers of my nozzle width. If I have a part which is exactly two times (2X) my nozzle width, it should take two "runs". Same with a 3X setting - as long as I make my Shell Thickness the correct value. So, I thought I would be smart about creating this model - and make my walls 1.05mm in width to get both efficient printing and strong walls. Three runs with my 0.35mm nozzle, and no inefficient "fill" (which has a tendency to be done with tiny back-n-forth x/y strokes) - right?
|The printed box with cover|
CURA was doing something strange with my box model - with walls equal to 3X my nozzle width. It would either not make solid walls - or it would use my "FILL DENSITY" setting to inefficiently fill the tiny space between the outer and inner walls of the box. No matter what I did, the model would either not print solid walls (fill density of zero) or would take 68 minutes to finish due to the crazy movements of my print head to fill a space which hardly existed.
The ExperimentI created a simpler square box - just one compartment - 20mm square - with walls which were exactly the thickness of my nozzle width - 0.35mm.
|The 20mm simple box showed a 33% estimated improvement in print time|
I tried the same box experiment with a 1.05mm wall width and Shell Thickness setting, and CURA would happily print the walls, but it would not fill the middle space - unless I used fill density (any value actually). But again, when I changed the Shell Thickness setting down by one-hundredth of a millimeter (0.01mm) to 1.04mm, Viola - it printed the walls with 3 straight-line runs, as I wanted in the first place. As you can see from the two screen shots, even this simple model had a reduction in estimated print time of 33% (from 15 minutes to 10 minutes).
The SolutionI then took my existing 1.05mm wall, multi-compartment box and changed that setting to 1.04mm "Shell Thickness" (leaving "Fill Density" at ZERO) - and BAM! The walls showed as solid - 3 runs of plastic. MOST IMPORTANTLY, with this one tiny change - hundredth of a millimeter on one parameter - the time to print on my box model went from 68 minutes to 26 minutes - a 62% reduction in time!
Summary Data:Walls of box: 1.05mm
Shell Thickness setting: 1.05mm
ACTUAL Print time: 68 minutes
Walls of box: 1.05mm
Shell Thickness setting: 1.04mm
ACTUAL Print time: 26 minutes