Although the model material is quite strong, since it is built up in layers, a
printed part will not be as strong as a cast or machined part. Most signifi-
cantly, the parts have different properties based on part orientation: the parts
are weaker between the layers than in the X and Y axis. Under extreme loads,
the layers have been known to delaminate . This is something to keep in mind
when designing parts for strength.
Throughout this chapter, we have discussed the strengths and weaknesses
of ABS and PLA as materials. Throughout the 3D printing community, this
has been a subject of much debate and has few definitive answers. For ex-
ample, PLA will shrink less than ABS, but that doesn't necessarily make it a
superior material. For many models, ABS' shrinking properties mean better
performance for overhangs and bridges.
One thing that is definitive is that ABS is a more ductile material. This means
it deforms and flows more readily. This has implications in your models. Fea-
tures like living hinges and snap fits rely on material deformation, which lends
itself to ABS. Another implication is failure mode . ABS parts will flex and
stretch while PLA parts tend to crack or shatter. ABS is better at accepting
inserts or being tapped. But even this is generalization, as plastics of either
type from different vendors (or even different colors) may have slightly dif-
ferent properties. To best understand the limits of the materials, you simply
have to experiment, and print a lot! It's part of the fun of owning a MakerBot.
Sizing and Scaling Models
If dimensional accuracy is very important to your model, you should design
the model to scale within the modeling program that you are using, account-
ing for plastic shrinkage. Most modeling programs also have the ability to
scale a model up or down.
Otherwise, you can easily scale your model in MakerWare before making it.
If you use a Mac, you can use the nifty program Pleasant3D
to resize STL files. It also doubles a GCode visualizer and an
ASCII STL to binary STL converter.