Scaling down a model for (much) faster 3D Printing

Those Minecraft (tm) tools I printed were really a big hit (with the kids) but they were quite big - The shovel came out at about 96mm (3.75 inches) - so you can imagine the charms were a bit too big for a keychain - about double the size and volume of a normal house key. I call them BackPack charms for that reason. The other problem was, they took a dogs age (whatever that means) to print. Those original set of 4 tools (all in one model) took almost 4 hours!

But what if I scaled them down in size? Would half the size take half the print time? I decided to experiment. I scaled down the tools to 3 different sizes to see what the effect was on size, print time and appearance. I used the Slic3r app to do the scaling - meaning I used the same source .STL model that came out of Autodesk 123D and scaled it 3 different times to generate 3 new .gcode files for my printer.
I printed at 100% (the original print), 50%, 35% and 25%.

Size

This was simple and accurate. The dimensions of the scaled down model were exactly scaled to the target ratio. For example - The original shovel was 96mm long, the 50% scaled was 48mm long. The 35% shovel was 34mm, the 25% was 24mm. Perfect. That said - visually, those scaled down versions looked unexpectedly smaller than their ratio due to the uniform scaling of all 3 dimensions - there was just less heft/volume overall - but they were accurate when measured. The 25% printed versions were miniscule

Print Time

This was not obvious, but the results were very encouraging. The reduction in size for a model scaled to 50% is much less than half the time - in fact, the 50% scaled print took 15% of the time. Rather than 238 minutes, it took just 36 minutes! This finding would impact my early prints of almost everything from this point forward. My next quest will be to come up with a semi-accurate estimation formula of print time. I'm sure that's achievable.
UPDATE (2/2/2015):  This might be a good place to use the "Square-Cube Law" - which states (among other thigs) that "...new volume is proportional to the cube of the multiplier." - which applies to the print time too, perhaps, since the cube of 0.5 is 0.0625 (one eighth) - so 238 minutes, at 50% size predicts a print time of 14+ minutes (actual time was 36 minutes, so this still needs some work).

Data

The 3D model of these tools can be found on Thingiverse.com. I did not create the original model, I just enhanced it to have keychain holes in all the handles.


(yes, Minecraft is now probably a trademark of Microsoft, inc.)