second worked well (Figure 5). I was printing using ABS.
It’s stronger than the PLA often used, but requires a heated
bed. The problems in the first print were due to the bed
not being level. I’ve also found that having the printing
heads and the bed a little hotter (+ 5°C) than recommended
in the software helps get the first layers to stick securely.
The design had a lot of overhangs, so I set “supports”
on. This prints little scaffolding structures under any
overhang (Figure 6). These are fairly easy to remove, and
with a two-head printer you can even print them in a
different color or in a dissolvable plastic. I’ve found,
however, that printing with two heads often gives problems
when build-up on the second head catches and damages
the main printing. To keep it simple, I simply used the same
head to print both the part and its supports.
When I got the first chassis home, I found I had made
another elementary mistake.
I had not left quite enough space between the two
motors so when one was fitted, there was not quite
enough space to squeeze the other one past it and into its
recess. No matter how much I tried, they were not going to
go in. It only took an hour with the CAD modes to add
another 1/4” to the chassis width. Now that I had plenty of
weight allowance with the change to being an Antweight, I
printed a new chassis and the other panels with six layers in
the skin and 50% fill (Figure 7). These were about 50%
heavier, but should be a lot tougher.
The parts needed quite a bit of cleaning up. Small
bores and the countersinks were re-drilled to size, and all
the supports cut or scraped out. The motors were fitted
with two 2-56 x 1/8” screws (Figure 8), and the power-on
switch was secured by two #2 x 1/2” self-tapping
metalwork screws (Figure 9). A yellow power-on indicator
LED was fitted in the opening provided for it in the design
42 SERVO 07.2014
FIGURE 7. Printed parts.
FIGURE 6. Printed support
FIGURE 5. First print.
FIGURE 4. Finished design.
FIGURE 2. Making bubbles.