well, especially if using a larger or smaller fan motor or aluminum
bar. We also recommend using plywood as the base since it is less
likely to warp or shrink over time compared to many other types
of inexpensive woods.
To build the OPN Minifuge (Figure 2A), readers should follow
the steps below, and we recommend reading the entire set of instructions first to become familiar with the process before trying to make
1. Start by making the tube holder (Figure 2B) out of the aluminum bar and wooden disk.
A. Use a hack saw to cut a 6.5-inch length from a 1-inch-
wide flat aluminum bar that is 1/16th of an inch thick
(tracing out the cut line in advance can lead to a straighter
edge). Then, use a metal file or sandpaper to smooth the
edge of the bar as needed. For schools that have a metal
shop, a band saw, chop saw, or metal shear could be used
to cut the aluminum bar.
B. Alternatively, if readers have difficulty obtaining a 1-inch-
wide × 1/16-inch-thick aluminum bar, other soft metal
bars (e.g., brass) will suffice. Readers could also use a hack
saw, band saw, or metal shear to cut a 6.5 × 1-inch rectangle from a 12 × 12-inch aluminum plate that is 1/16 inches
C. Next, use a drill press or a hand-held power drill to drill
two 7/16-inch-wide holes at the opposite ends of the alu-
minum bar, since this diameter should hold many com-
mon microfuge tubes. However, make sure to measure
the tubes in advance in case larger or smaller holes are
needed. Also, each hole should be centered 5/8 inch
away from the end of the bar along the mid-line (marking
these locations in advance should result in better placed
holes). Importantly, when drilling these holes, make sure
to secure the aluminum bar in place (e.g., by using a vice
that is bolted to the drill platform or tabletop, or by plac-
ing the aluminum bar on a wooden board and then using
at least two clamps to hold the bar and board to the drill
platform or tabletop, so that they will not move).
D. After drilling these holes, bend the aluminum bar to a 30˚
angle, 1 inch from each end using a vice and a protractor
to measure the angle. Also, make sure to bend each end of
the bar in the same direction, so that both point the same
way (Figure 2B). Alternatively, in schools that have a metal
shop, the bar can be bent in a “brake” ( i.e., a machine that
bends sheet metal).
E. Once finished with the aluminum bar, make the wooden
disk by cutting a 3/8-inch long piece off of a 1-inch diameter wooden dowel. Since this piece should be flat and
level, consider using a chop saw for this step. Alternatively, some hardware stores or lumber yards may cut this
piece for free when purchasing the dowel. However, if cutting a wooden dowel proves too problematic, readers can
instead use a circular flat-head plug with a 1-inch diameter
as their wooden disk. Although these plugs are usually
¼ inch thick, they should provide enough clearance for
the aluminum part to spin above the motor casing.
F. Next, use sandpaper to rough up the bottom of the aluminum bar near its center and the top side of the wooden
disk. Then, epoxy these two pieces together, making sure
Figure 1. The parts and materials used to make the OPN
Minifuge. (Epoxy labels have been blurred to obscure the
brand, since any commercial quick-drying epoxy product can
Figure 2. The completed OPN Minifuge. (A) Overhead view.
(B) Close-up of the motor assembly.