An Inexpensive, Open Source Clinical Centrifuge
An Inexpensive, Open Source Clinical Centrifuge Made from a Box Fan and a
Large Plastic Tub
Zachary WareJoncas, Chris Stewart, John Giannini*
St. Olaf College, Biology Department, 1520 St. Olaf Avenue, Northfield, MN 55057
* Email: [email protected]
Abstract
A critical piece of equipment in any biology lab, the centrifuge is needed to perform a
wide array of experiments. However, the cost of such equipment often limits the educational
opportunities available to students in a teaching lab. To help address this situation, we describe
how to build a low-cost, open source clinical centrifuge using commonly available parts, such as
the motor from a box fan and a large plastic tub. The centrifuge itself spins at between 1,150 and
1,550 rpm, and its speed can be further slowed using a commercial “dimmer” switch. Because
the plans and materials used to make this centrifuge are all open access, we call our design “the
OPN Centrifuge,” and we hope that it will help to expand the educational experiences available
for biology students at many different levels.
Keywords
Inexpensive, Open Source, Do-It-Yourself (DIY), Homemade, Clinical Centrifuge,
Teaching Lab
Introduction
Although many biology experiments can be conducted without a centrifuge, the presence
of a clinical centrifuge in a teaching lab opens up numerous possibilities for students. For
example, with a clinical centrifuge, students can spin down whole cell cultures for large volume
experiments or isolate organelles from those cells (e.g., mitochondria or chloroplasts) to
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investigate specific cellular processes, such as respiration or photosynthesis (Graham, 1999;
Johnson & Lardy, 1967; Stenesh, 1984; Clark & Switzer, 1977). Consequently, having a clinical
centrifuge available can significantly expand both the number and nature of experiments that
students can conduct in an educational setting. Unfortunately, as with many pieces of scientific
equipment, a clinical centrifuge can cost hundreds or thousands of dollars, which often limits the
use of this important tool in many schools.
Although a number of innovative centrifuge designs using household or other items have
been published in the literature (Brown, et al., 2011; Mabrouk and Ezz, 2012) or online (Science
Buddies Staff, 2014), some of these models are too specialized for an introductory teaching lab
(Kimball and Ferguson Wood, 1964; Donze and de Groot, 1982), and others cannot handle the
high volumes needed for lab preparations (Boliston, 1977; Moran & Galindo, 2011; Grushkin,
2013). We therefore explain how to build a “homemade” clinical centrifuge using a box fan and
other common supplies (Table 1) for a total cost of between roughly $30 and $65 depending on
the exact items used (not including the price of tools). Readers will further need a band saw,
drill press, hand-held drill, standard vice, scissors, screw drivers, pliers, wire cutters, wire
strippers, hobby knife, electrical tape, heavy-duty tape, and epoxy or super glue to assemble the
centrifuge, and these tools should generally be available in a high school, college, or university
wood or metal shop.
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Table 1: Supplies Used to Make the OPN Centrifuge
Item
Approx. Cost
20-in box fan
$10 to $25
18-gal, flat-bottomed plastic tub
$7 to $15
1
12-in x 12-in x /16-in aluminum plate
$6 to $12
(cut to 9-in x 3-in using a band saw)
Two 8-32 machine screws with combo round
$1 to $2
heads (¾ in long) with nuts
10-in x 10-in x ¾-in wooden board
$1 to $2
Eight #6 drywall screws (¾ in long, course)
$1 to $2
Four #6 drywall screws (2 in long, fine)
$1 to $2
Thirty-two ¼-in x 1-in Fender washers
$2 to $4
Total
$29 to $64
Like other equipment that we have developed, the materials needed to construct this
centrifuge can be purchased at hardware stores or online and easily assembled with limited
experience. Because these parts and plans are all open access, we have named this design the
OPN Centrifuge, and we invite others to use or modify these plans to fit their particular
educational or research needs.
Materials and Methods
To assemble the centrifuge (Figure 1), make sure that the fan is unplugged and then
remove the motor, switch, and power cable from the casing. Next, remove the fan blades using
the wire clippers and scissors, which should increase the speed of the completed centrifuge. To
do this, make repeated cuts with the wire clippers along the fan blades as close to the hub as
possible and follow up with the scissors as needed (Figures 1 and 2).
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Figure 1 The fully assembled OPN Centrifuge.
To complete the rotator assembly, create the tube holder (Figure 2) by first using a band
saw to cut the aluminum plate to a 3-inch by 9-inch bar. Then, use a drill press to drill a ⅞-inch
hole ¾ of an inch from each end of the aluminum bar (along the center line). Next, use a vice to
bend each end of the bar to a 35˚ angle 15/16 inches from each end. Also, if the plastic fan head
has a raised “button” in the center of its face, drill a hole in the exact center of the aluminum bar
to fit over this “button” (Figure 2). Then, center the bar on top of the fan head and drill two 11/64inch screw holes that are 1¾ inches on each side of the center of the bar and into the plastic fan
head (alternatively, readers can use a No. 29 drill bit for this step). Finally, use the two 8-32
machine screws and corresponding nuts to hold the fan head to the bar, which will complete the
rotator assembly (Figure 2).
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Figure 2. The completed rotator assembly of the OPN Centrifuge.
Next, attach the wooden base to the flat-bottomed, 18-gallon bucket. If the bucket has a
raised “button” in the center of its “floor,” use a hobby knife to remove the “button,” which will
prevent the assembly from wobbling when the centrifuge spins. Then, center the wooden base
inside the bucket and secure it using eight #6 screws (¾ inches long) drilled in from outside of
the bucket (one screw should be placed near each corner of the wooden base, and the other four
should be placed in a similar square pattern closer to the center of the base). This can be done by
placing the bucket on its side and holding the wooden base up against the “floor” of the bucket.
Even though these screws should not pass through the ¾-inch wood, for safety reasons, do not
place your hand over the area where you are drilling.
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Once finished, attach the rotator assembly to the wooden base using the screw brackets in
the four corners of the motor casing and the fine-threaded #6 drywall screws that are 2 inches
long (Figure 3). Depending on the make and model of the fan, however, a different type of
screw may be needed. Also, before screwing the assembly into the base, stack eight ¼-inch x 1inch Fender washers below each screw, so that the rotator assembly will sit slightly above the
wooden base when the two items are screwed together (gluing each set of washers together in a
stack beforehand makes it easier to work with them). This additional space is necessary, so that
the electrical wires running from the fan motor can be threaded underneath the assembly without
the motor resting directly on top of them, which would cause a dangerous wobble once the
centrifuge began spinning.
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Figure 3. Motor casing attached to the wooden platform using 2-inch long, finethreaded #6 drywall screws and four stacks of eight ¼-inch x 1-inch Fender
washers in each corner (arrow).
Finally, cut a hole near the bottom of the bucket, for the power cable and switch. Use a
large (1-inch) drill bit to make this hole in the side of the bucket as near the bottom as possible.
Then, enlarge this hole until both the plug and the fan switch (with the knob removed) can be fed
through the hole. Next, tape down the electrical wires both inside and outside of the bucket,
using heavy duty tape (Figures 1 and 2). Once plugged in, the centrifuge should run at the three
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speeds on the switch. If not, unplug the electrical cord and ensure that none of the wire
connections have become loose during construction.
Hazards
Because working with power tools, hand tools, and electrical wiring can be dangerous,
please exercise great care and the proper safety techniques when assembling the OPN
Centrifuge. For example, make sure that the fan is unplugged when taking it apart and working
on the electrical wiring. Also, verify that all electrical connections are properly made and
insulated from outside contact (e.g., no exposed wires) before using the device. Also, for those
who are unfamiliar with the tools and techniques described above, please work with an
experienced technician to avoid injury.
Calibration and Testing
We calibrated the OPN Centrifuge using a stroboscope and found that it spun at between
roughly 1,150 and 1,550 rpm on the “low” and “high” settings, respectively. Given the 125-mm
distance to the middle of each centrifuge tube, we calculated the corresponding g force to range
between 185 and 336 g. By further plugging the fan motor into a commercial “dimmer” switch,
we could reduce the above speeds to about 375 and 450 rpm, respectively, resulting in forces of
between 19.7 and 28.3 g. As a result, the device has the potential to operate over a wide range of
speeds and, thus, generate a corresponding range of forces.
In addition, as an endurance test, we ran the OPN Centrifuge for over 9 continuous hours
with two centrifuge tubes in it (each containing 10 mL of water), and the device operated without
incident or mechanical failure.
To further test the OPN Centrifuge, we spun down 5-mL samples from cultures of
Tetrahymena thermophila, sampling the middle of the supernatant column onto microscope
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slides, and counting ten fields of view for remaining cells. We repeated these tests twice and
found that, on the “high” setting, the centrifuge removed the vast majority of cells from the
supernatant after just 15 seconds with complete pelleting after 45 seconds (Figure 4). We then
confirmed that the cells remained viable after centrifugation by spinning down 5-mL samples
from two different cultures for 60 seconds (on high), pouring of the supernatant, suspending the
pellet, and viewing a 30-µL sample at 40x magnification.
Relative Frequency
1
0.8
0.6
0.4
0.2
0
0
10
20
30
40
50
Time Spun (s)
Figure 4. The relative frequency of Tetrahymena thermophila cells in the
supernatant as a function of time spun (0, 5, 15, and 45 seconds) on the
“high” setting.
Discussion
Given its affordability and simplicity, we hope that the OPN Centrifuge will be a useful
tool for teachers and students alike. For example, by expanding the experimental possibilities in
an instructional lab, this centrifuge can broaden the scope of the biology education that students
receive while also providing them with new opportunities to develop more sophisticated
laboratory techniques. In the process, students should hopefully become even better prepared for
more advanced courses or more complex work in a research or laboratory setting.
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In addition, as with other OPN instruments and equipment that we have developed, we
encourage readers to customize the OPN Centrifuge to fit their specific educational or research
needs. For example, while the version described here has a maximum speed of approximately
1,550 rpm, which generates a force of roughly 336 g, modifying the fan speed (e.g., by using an
adjustable “dimmer” switch) or changing the radius of the tube holder will change the g-force
generated. Readers can further drill holes into the plastic caps of standard centrifuge tubes to
hold micro-centrifuge tubes for smaller scale experiments. Also, instead of using a plastic tub to
house the centrifuge, readers could instead use another type of container or even make a large
wooden box with a lid to house the device. Thus, we hope that the versatility of this design will
help to make the OPN Centrifuge an important multi-purpose tool in many educational and
teaching labs.
Disclosures
The authors declare that they have no conflicts of interest. We, in fact, encourage readers
to experiment with different materials to improve upon this design.
References
Boliston, T.A. (1977). A simple, home-made haematocrit centrifuge. Anaesthesia,
32(4), 355-356.
Brown , J., et al. (2011). A hand-powered, portable, low-cost centrifuge for diagnosing
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Clark, J.M. and Switzer, R.L. (1977). Experimental Biochemistry (pp. 57-64, 291-296).
San Francisco, CA: W.H. Freeman & Co.
Donze, M. and de Groot, H.P. (1982). A cheap high-capacity continuous centrifuge. J.
Plankton Res., 4(1), 187-188.
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Graham, J.M. (1999). Isolation of mitochondria from tissues and cells by differential
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