Creating or obtaining a water tight thing used to be one of the most bother-
some tasks for the early MakerBot adopter. Your STL file must be one con-
tinuous, solid, manifold object. A manifold object is essentially “water tight”.
If there are any holes, gaps, overlapping vertices and/or faces, in the model,
the software for the 3D printer will not be able to tell what is inside the object
and what is outside. There are tools that can help identify and close such
holes and gaps, but for best results you should address these potential de-
fects as you design your object.
If you can't get your design software to give you a watertight object, you can
repair your STL file in either MeshMixer or netfabb. To learn how to use net-
fabb and MeshMixer to repair STL files, see Chapter 9 .
When you design a thing that is very wide and long and flat, the corners will
often curl while printing. This occurs because as the extruded plastic cools,
it will shrink a bit. This is a bigger problem for ABS than for PLA, but it will
affect both materials. The easiest way to minimize corner curling and shrink-
age by enabling a raft when you are slicing your model. A raft is a large flat
lattice work of printed material underneath the bottommost layer of your
printed object. Use of a raft will help reduce warping and curling by allowing
your printed object to adhere better to your flat build surface.
Some users address corner warping by printing with shields or baffles en-
closing their build volume. The purpose of these baffles is to prevent slight
drafts of colder air from cooling the base of the build and to generally create
a more consistent temperature. MakerBot in-house designers plan for this
shrinking effect when designing their models. They will often add mouse
ears , which are a small flat circular structures on the corners of a large model.
This design feature acts as a mini-raft for the thing allowing it to better adhere
to the build surface and to cool at a more uniform rate.
Even if you're printing in PLA, you may be sharing your design
( Chapter 10 ) with people who are using ABS or older, more
finicky printers. So, it's helpful to be aware of these constraints
even if you're enjoying trouble-free PLA printing on your Rep-
Friction Fit and Moving Parts
As you create your model, be sure that there is enough clearance between
moving parts such as gears, cogs, or links in a chain. If there is not enough
space between parts, your prototype may be a solid, non-moving object. For