Graphics Reference
In-Depth Information
parts that need to move freely, 0.4 to 0.5mm clearance on all sides usually
provides enough room for easy movement. Parts that need to be fit together
snugly require only about 0.1 to 0.25mm clearance on all sides to ensure the
parts don't come apart easily.
Some interesting examples of linked prints with moving parts are the Mak-
erBelt by makerbot (
http://www.thingiverse.com/thing:31243
) and the
Chain Generator by Sal (
http://www.thingiverse.com/thing:28405
).
Another awesome example of flexible prints is Zomboe's Chainmail (
http://
www.thingiverse.com/thing:8724
) that PrettySmallThings derived to create
her fully printable clutch purse (
http://www.thingiverse.com/thing:31234
).
The Printable Brain Gear (
http://www.thingiverse.com/thing:14407
)
is a
good example of both gears and friction fit, as are the Nautilus Gears men-
tioned in
Figure 7-5
.
Designing a Part to Be Dimensionally
Accurate
The Replicator 2 is an incredibly precise machine. Still, for engineers and
designers who require dimensionally accurate parts, the precision of the part
is subject to the shrinking effects of the material. ABS has a uniform shrink-
age rate of about 2%. So if you need precise measurements, you need to
account for this in your model. PLA shrinks about 0.2%, which makes it a far
better material for printing very accurate parts. Either way, its something to
plan for when designing for a MakerBot.
Surface Finishing
There are a few things to keep in mind when trying to achieve a very fine
surface finish. Curved surfaces generally have smoother finish than flat ones.
Things that generate a closed tool path with no breaks give a higher quality
part. In other words, if you design a wall to one extrusion width, it needs to
be a closed curve or over a certain length or it won't build reliably. If you make
it two or four thicknesses, it becomes its own closed curve. In general, things
that generate short toolpaths, even if they are closed curves, are a problem,
as the material doesn't have enough time to cool (though the active cooling
fan on the Replicator 2 helps this a lot).
For any model, a small amount of post-finishing goes a long way. Models can
be sanded and retouched. For ABS parts, a little acetone will help to smooth
out small defects. Some people use wood putty, enamel based paint, mod-
eling epoxy, or spray paint to smooth out the surface.
Metal finishes for 3D printed objects are also being developed. Cosmo Wen-
man is currently working on making publicly available his line of
Alternate
