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Homemade shaking incubator

Bob Horton horto005 at maroon.tc.umn.edu
Wed Mar 6 11:06:24 EST 1996

Bob's Homemade Shaking Incubator Design


This is my design for an easy-to-build and inexpensive laboratory
shaker/shaking incubator. It will undoubtedly remind many readers of
something they may have built for the Science Fair in the 5th grade, but
as far as I know, the use of record-player power and the hanging
platform are original. And, hey, you can't argue with the price.

Three figures are attached. The attachments are MIME-encoded, and should
be decodable with any MIME-compliant newsreader, including the one built
into NetScape 2.0. The figures are small, black and white drawings in
GIF format, and should be viewable from any web browser, once they are
decoded. This design is also available on my web page at

Figure 1: Parts for the Home-Made Shaker.

Figure 2: Additional Parts for the Shaking Incubator.

Figure 3: Portrait of the Final Product.


The shaking platform is cut from a particleboard sheet the same size as
the top of the box; the rest of the sheet is used to reinforce the top
of the box. The platform is suspended from the edge of the top opening
with strings. Slipknots are used in the strings to make them easy to
adjust until the platform is more-or-less level. Then the knots are
secured in place with tape. The strings and holes are arranged so that
the strings hang as vertically (i.e., parallel to one another) as
possible. This way the platform will remain essentially level as it
swings around in a circle.

A bolt is mounted on the turntable, and passed through a hole in the
platform, so that when the turntable spins, the shaker moves in an
orbital motion. Note that it takes very little work on the part of the
record palyer motor to move the platform in a horizontal circle, even if
it carries significant weight.

The heat source (light bulb), fan, and thermostat are mounted on a
particleboard base, and wired so that the fan is always on, but the
light bulb is turned on and off by the thermostat in classic Jr. High
School Science Fair fashion. The whole heat-control unit is placed in
the incubator box, and a thermometer is used to calibrate the
thermostat. The thermostat I use keeps the box somewhere 35 and 38
degrees centigrade. I think a regular home thermostat would work better,
but the bugs don't seem to mind.

The fan blows air around fast enough that air in the whole box is very
close to the same temperature. But I put the thermostat probe behind the
fan so it would not detect radiant heat, and the light is below the
platform so it doesn't shine right on the cultures.

I covered the areas of the cardboard walls and the portion of the bottom
of the platform that come close to the light bulb with foil, to reflect
some heat so they wouldn't be quite as likely to catch fire. If you fold
several thicknesses of slightly wrinkled foil together, they make a nice
shield against radiant heating (this was the suggestion of Mike Herron,
from the lab across the hall).

The box is sealed with masking tape, except for the top opening. A lid
(not shown) is made of an additional cardboard sheet, edged with soft
foam weather stripping. This type of flat lid limits the height of
culture flasks to the distance between the shaking platform and the top
of the box; alternatively, a raised lid made of a second box would allow
more room.

This shaker has three speeds; 33, 45, and 78 rpm. The fastest setting is
still somewhat slower than typical bacterial culture conditions, but it
works OK if you leave plenty of air in your flasks. A faster motor could
be substituted for the record player, but it wouldn't be as cute.

The heating unit and the record player can both be plugged into a power
strip, so a single convenient switch can be used to turn the whole thing
on and off.

The tools required are fairly simple:

* wrench, pliers, screwdriver, etc. to remove any parts of the record
player that stick up too high.

* drill to mount the bolt on the turntable, and make holes for the

* knife to cut cardboard and strip insulation on the wires.

* jigsaw to cut the platform from the particleboard.

My estimate of the cost of materials is as follows:

* cardboard box, string, tape, etc.: $0.00

* record player: $0.75 (yes, I can get them in Minneapolis for 75 cents
at the "Digger's Delight" behind Goodwill on Como Avenue near Highway
280. Otherwise they may run you 5 bucks apiece at a garage sale).

* thermostat: $3.50 from AxMan surplus, University Ave., St. Paul. At a
hardware store, these cost about $12.

* fan: $7.50. I used a 120V AC box fan, about 4 inches in diameter
(AxMan Surplus). I couldn't find one the right size at Digger's, but
keep your eyes peeled.

* light socket: $0.85 (hardware store)

* weather stripping: ~$3

* power strip: ~$3.50 (only used for the Shaker Deluxe). 

* thermometer: $1.19

I scrounged the light bulb and the particleboard. (Retail ~$3?)

So I have over $20 invested in my shaking incubator, and it could easily
cost over $23 if you had to buy particleboard and stuff.

Old record players also make great sample rotators, if you set them at a
steep angle, or they can be used to wash gels and blots, if you put your
pan on the turntable and slightly raise one end of the record player.

The only shaking incubator I have in my current lab is of this design
(serial number 00000001). I have used it to grow 50 ml E. coli cultures
in LB, in regular 500ml Erlenmeyers, and 1.5ml cultures in TB in 15 ml
snap-cap tubes.

I have recently used this incubator to clone a cDNA sequence for a novel
human neurotransmitter receptor subunit. But I'll try not to let Real
Science interfere too much with inventin' stuff. :)

Happy shakin'!

Bob Horton
horton at biosci.cbs.umn.edu
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