D. After finishing the hole in the front face, repeat this process in the same location of the back face, so that the DC
jack can later be inserted there.
E. If the holes are placed in these locations, the switch and
jack should be out of the way of the tube holder as it spins.
Of course, depending upon the exact switch or jack used,
readers may need to place these holes in different locations
(e.g., just under the raised ridge that extends around the
bowl) or use larger or smaller holes. For these reasons,
readers should measure both the length and diameter of
these components in advance to make sure that the holes
are both the correct size and placed in the proper locations.
F. Alternatively, readers can wait to drill the holes for these
components until after securing the finished motor
assembly to the plastic bowl and plywood board (Steps
6A–6C below). This approach may enable some readers
to better place the holes for the switch and jack, so that
they can stay out of the path of the spinning tube
holder (especially if using a different plastic bowl).
6. Next, screw the completed motor assembly into the plywood
board through the bottom of the plastic bowl (Figure 2B).
A. To do so, first center the completed motor assembly on
the bottom of the bowl, and then center the bowl on
top of the plywood board.
B. Next, predrill the holes for the screws through the bottom
of the plastic bowl and into the board, using the holes in
the corners of the fan motor casing to line up the drill
bit. It is important to predrill these holes into the bottom
of the bowl because the plastic may crack if the screws are
sunk directly into the bowl without predrilling. Also,
make sure to use a drill bit that is smaller than the diameter of the screw (e.g., for #6 screws, we used a 3/32-inch
drill bit). Otherwise, the screws may not grip the plywood
and hold the motor assembly in place.
C. Once the holes have been predrilled, screw the completed
fan motor and tube holder, plastic bowl, and plywood
board together (Figure 2B).
7. Next, push the switch and the jack into their respective
holes in the front and back of the bowl, and secure the components with the included washers and nuts (Figure 2A).
8. Then, with all of the pieces attached, use the additional
lengths of braided wire to connect the positive (red) wire from
the fan motor to the closest terminal of the push-button
switch, the other terminal of the switch to the positive terminal of the DC jack, and the negative terminal of the jack to
the negative (black) wire from the fan motor (Header Image;
Figures 2A and 5).
A. If the positive and negative terminals of the DC jack are
not clearly marked on the component, readers should
consult the spec sheet for the part. Alternatively, experi-
enced readers could use a multimeter to identify which
terminal is which, and other readers could ask an expe-
rienced technician for help with this process. We rec-
ommend identifying and labeling (if possible) the
positive and negative terminals of the jack in advance
because the centrifuge will not spin if the wrong
connections are made, and the circuit would then need
to be re-wired.
B. When wiring the different circuit components together,
make sure to use enough additional wire so that each
length can later be taped down to the bottom or side of
the plastic bowl and, thus, remain out of the way of the
aluminum bar and microfuge tubes when the centrifuge
spins (Figure 2). Also, if too much wire is used, readers
can simply cut off the excess length before making their
C. To splice two pieces of wire together, simply strip off
roughly 1 inch of plastic coating (insulation) from the
end of each wire, twist the exposed leads together, and
then wrap the bare wire with electrical tape (starting/
stopping about 1 inch above/below the exposed wire
to ensure an insulated connection).
D. To connect a piece of wire to one of the terminals of the
push-button switch or DC jack, follow a similar approach,
except twist the bare end of the wire tightly, thread it
through the hole in the terminal, twist the wire back
around itself, and wrap it with electrical tape as previously
E. Also, for permanent connections, readers can solder the
wires together using a soldering iron and electrical
Figure 5. A circuit diagram showing the wiring for the OPN