term 3D printing broadly describes the creation of objects
by additive manufacturing whereby the object is built up from
successive layers, these layers can be formed from any fusible
or bondable material. High resolution professional 3D printers
use lasers or light to cure photopolymer resins layer by layer
in a bath or jetted from a nozzle in a similar fashion to
an inkjet printer. Not only are these printers too expensive
for the home user but also the cost of the photopolymers they
use is relatively high. No doubt such machines will eventually
become available at an affordable price for the home user.
Currently the printer most likely to be adopted by the hobby
or home user in terms of both capital and running cost is
the fused filament type, it is such a machine that I have
used for the following exercise.
Filament printers form the layers by extruding molten thermoplastic
material through a nozzle and spreading the plastic onto the
previous layer, the height of each layer depends on the height
of the nozzle above the preceding layer and the width on the
volume of material extruded. At first sight this appears a
rather crude method and would be but for the sophisticated
digital techniques available to control the flow of material.
There are several major issues with 3D printing generally
related to available resolution and at least a basic understanding
of these is required before we examine how to minimize them
in order to achieve an acceptable finish. The higher the resolution
of the printer the less pronounced these become but with fused
filament printers resolution is limited by the minimum nozzle
diameter through which we can reliably extrude the molten
Fig.1 Stepping on curved surface
1 illustrates how the printer software attempts to conform
to a 6mm radius curved profile while constrained by the extruded
filament cross-section from a 0.4mm nozzle and 0.2mm layer
height. Layer by layer the printer first prints the perimeter,
shown shaded, and then fills in between. Most entry level
'off the shelf' 3d printers run most reliably at 0.2mm layer
height but we need a higher resolution for our models. It
is interesting to note that many of the samples produced to
promote these printers are designed to appeal even at these
above illustration is for a solid where the extruder always
has a previous layer to print on to but what happens when
we want to print something hollow? Professional printers have
a second extruder that prints a dissolvable support material
where required but our fused filament printer will not have
that facility. It is possible to have 2 extruders but the
support material will either be the same as that used for
the main body of the print or a special material requiring
additional equipment to remove it from the finished print.
Down to about 45 degrees the printer will print overhangs
so in the following illustration (fig.2) the first eight layers
would not require support but the succeeding layers would.
It is possible, and the software will cater for this, to print
support structures using the same nozzle and material as depicted
in the picture. At larger scales this may be practical but
as you can see from the picture is far from ideal in 4mm scale
as it is difficult to remove the support structure without
damaging thin profiles.
Fig. 2 Unsupported layers in hollow forms.
this point you may well be writing off 3D printing at home
and you would be right if you were hoping to print one-piece
body shells but the forgoing was written to demonstrate that
was impractical. Now let us take a different perspective and
design our model around separate component parts, doing so
will allow us to explore designing and orientating each component
for best results. Printing the curved solid vertically as
in fig.3 for example avoids both the stepping and support
issues, we still have the striations but these are a lot more
manageable. Note that in the diagrams the layers are accentuated
and in reality each layer will be 0.048mm (48 micron).
Selecting orientation for best results.