The Turbo Cat
II Stove
The Turbo Cat
II alcohol stove is a lightweight backpacking stove with an optional adjustable
temperature ring and a simmer top that can be used when low heat is required.
The stove can be used with or without the simmer ring and top. At full heat
output, this stove will boil 2 cups of cold tap water in approximately 4
minutes 30 seconds using less than 1 tablespoon of fuel. With the simmer ring
adjusted for minimum heat, the stove can simmer a meal for 30 minutes with only
one tablespoon of fuel. This stove design requires some extra construction time
but the benefit is improved heating, flexibility, and a quality simmering
control.
Background
The first
alcohol stove that I built was Roy Robinson’s Cat stove. The ease of
construction and quick lighting appealed to me; however, heat control with a
sliding simmer ring is unpredictable due to the open stove bottom and uneven
camping surfaces.
I spent the
next four months building and varying Don Johnston’s sealed soda can stove
design. During this period, I constructed over 45 alcohol stoves modifying
individual details to determine the impact. I used this optimized sealed soda
can stove entirely during the last two years of hiking and backpacking. The
lack of heat control and additional preparation for lighting; especially in
cold weather, was bothersome.
I recently
returned to the workbench with the goal of improving the Cat Stove design. The
results of this effort is the Turbo Cat II stove which has a sealed bottom, an
adjustable temperature ring with limit stops, and a simmer top for extended low
heat cooking.
The Turbo Cat II
Stove Assembly
Begin by
carefully placing a 1-1/2" hole in a 5.5oz cat food can along the can's
inner detent. Once the can is scoured, the knife tip can be poked through the
can and the cutout carefully removed. A chassis punch can be used to make the
hole if this is considered unsafe.
Clean all the
label glue from the cat food can by heating it slightly and wiping the warm
glue from the can with a paper towel. Be careful not to touch the hot glue or
can with your bare hand.
Next, drill
five 1/4" holes into the side of the can 7/16” from the bottom spaced 2”
apart. This will leave an uneven gap of approximately 2-5/8” between two of the
holes. This larger gap will be used to place the thumb rest. You may find that
marking the height of the holes first with a marker to be effective. Try not to
dent the can surface while drilling so the simmer ring surface remains smooth.
The inside of
the stove is made from a soda can bottom cut to a height of 1-3/8".
Using a ¼” paper
punch, place nine holes in the can 3/8" from the cut edge of the can. If
your paper punch is larger, simply place less holes in the soda can. Drilling
these holes is difficult since the soda can is so thin.
With a
scissors, cut a piece of uniform insulation that is a snug fit in the can
approximately 5/8" to ¾" thick. The height of the insulation varies
the flame height, color of the flame, and optimum stove to pot distance. The
insulation can easily be formed and compressed slightly after adding the first
tablespoon of fuel, prior to the initial burn. The insulation will maintain
it's height after the initial burn. The target depth of insulation is 3/4"
below the center of the stove and at least ½" below the sidewall holes
around the perimeter. If a mistake is made with the insulation it’s easy to
remove and replace after the stove is assembled. Simply cut the new piece of
insulation, lay it flat on the top of the stove, and press the center into the
stove. The insulation can be worked into position easily with a pencil.
Using an
aluminum sidewall from a second soda can, make a circle using the smaller
diameter end of the 5.5oz cat food can. Cut the aluminum slightly larger than
the mark with a scissors. Bent and trim the piece of aluminum piece until it
lays flat on the lip of the cat food can.
The stove is
assembled as shown below. Before applying epoxy to hold the stove together,
sand the surfaces where the epoxy will be applied removing all colored print.
Place epoxy on the mating surfaces of the inner can (top and bottom) as well as
the outside can ring. The epoxy should be J-B Weld Epoxy sold at Home Depot,
Walmart, and some automotive stores. It is packaged in two small tubes that
have to be combined in equal parts. There are several types of epoxy made by
this company and not all types can withstand the high temperatures. Part number 8265-S J-B WELD states on the upper left of the
reverse side that the product can withstand temperatures to 600 degrees F. I
have been told that 8270 ADHESIVEWELD, 8271 AUTOWELD, 8272 MARINEWELD, 8273
PLUMBERSWELD, 8280 INDUSTROWELD are also identical products in different
packaging. This has not been verified. The product called JB KWIK should not
be used.
Hold the
cover in place during the 15 hour curing time with another soda can and some
weight placed on the top. If the stove is used prior to a complete cure, the
epoxy will soften and turn black. The bottom of the stove is shown in the
photograph below.
Adjust Ring, Thumb
Rest, and Simmer Top
The stove can
be used without these additions or added later.
The rotating
adjust ring is constructed from a 5/8” X 12” residual piece of aluminum dryer
vent pipe from the windscreen construction. Score the aluminum first with a
straight edge and a carpenter knife, then bend the aluminum until it breaks. If
the aluminum is cut with a tin snips, the strip will have bends from cutting
that will have to be smoothed.
Bend right
angles approximately 3/4” from each end so that the outside dimension is no
greater than 10-1/2”. The softer aluminum dryer vent pipe works well because it
can be bent at sharp angles. Bend the adjust ring around the can. With the ends
pinched together, the ring should rotate with some friction. If not, reform one
end until it is acceptable.
Drill five ¼”
holes in the adjust ring. Place the first hole 1” from the tab shown in the
photo below at
Next, pinch
the ends together almost half way down the 3/4” tab and fold both ends back on
themselves as shown below. Later a small amount of epoxy will be applied to the
fold so it is securely held in place.
The thumb
rest is constructed from a 5/8” X 2-3/4” piece of aluminum dryer vent pipe.
Bend this strip at ¾” intervals to form the thumb rest shown below. Form the
thumb rest to the can then cut a ½” wide notch in the aluminum to form adjust
ring rotational limit stops. After the thumb rest is formed, bend a slight
detent in the tab that overlaps the adjust ring. This will allow the ring to
rotate without binding on the end stops.
Locate the
adjust ring and thumb rest on the can in the 2-5/8” gap between the vent holes.
When the thumb rest and adjust ring tab align, the vent holes should be open.
If the adjust ring is moved to the opposite tab stop, the vent holes should be
completely covered. If the holes do not align, rotate the adjust ring 180
degrees (flip it over).
Carefully
slide the adjust ring fold apart and place some epoxy on the tab and slide the
adjust ring back together. Be careful not to get any epoxy on the inside of the
adjust ring. Place epoxy behind the thumb rest and carefully position it so the
adjust ring can be rotated without obstruction. Place a small amount of epoxy
along edges of the thumb rest being very careful not to get any epoxy on the
adjust ring. Let the epoxy cure for at least 15 hours before using the stove
for the first time.
The simmer
top is used in conjunction with the adjustable ring to reduce the stove output.
The top is constructed from second cat food can that is cut to a height of ¼”.
Lay a marking pen flat on the table and rotate the can to place a guide mark on
the can. A tin snips is the best tool to use for this cut. Next place three ½”
holes in the top evenly spaced inside the detent. A uni-drill (stepped drill
bit) will make nice bur-free holes in the thin can material.
Windscreen and
Integrated Pot Support
Integration
of the pot support and windscreen makes a system that packs nicely and is very
light. To construct a windscreen for a 6" pot start with a 20-1/2" X
5-1/4" piece of aluminum. A good source of aluminum is a 4" dryer
vent tube available at many home stores. It's sold in 24" pieces that is
clipped together to form a 4" tube. This aluminum is soft and is easily
scoured with a knife and straight edge. Subsequent flexing will work harden the
aluminum at the scoured line and the aluminum will break right on the line.
The
use of aluminum roof flashing is not recommended since it is coated with a film
that has a shinny appearance. This film turns brown and gives off an odor when
heated by the stove. This aluminum is also harder and it will be difficult to
make the tight bends required to construct the thumb rest and adjust ring.
The
pot rests on support rods made out of coat hanger wire or 3/32" steel
welding rods. The use of stainless steel welding rod was considered; however,
there may be vapor concerns with the use of this material. The windscreen ends
overlap by 3/4" and are held together with a large straightened paperclip
weaved through the three vertical holes.
The
rod that holds the ends of the windscreen together has an angled loop on one
end and a bend tip on the other end. This allows the rod to be rotated slightly
as it is threaded through the vertical holes. The pot support rods are made
from 6-1/2” pieces of rod. The right angle bend is ¾” from one end.
Before using
the stove for the first time, remove sharp edges or burs from all surfaces with
sand paper or a file.
Completed Stove
This is a
photograph of the assembled stove when it's burning. The stove starts with a
smaller flame and then builds as the stove warms. Be careful, after the stove
is lit, the pot, support rods, and windscreen get very hot. When using the
simmer top, the adjust ring should be set prior to lighting the stove. Light
the stove without the simmer top, let the stove warm slightly, and then
carefully place the simmer top on the stove.
Fuel
This
stove only burns alcohol, preferably denatured alcohol. There are many sources
of denatured alcohol because it's sold in stores that sell paint or solvent.
This includes most hardware stores, Home Depot, Walmart, Lowes, etc. Another
acceptable source of denatured alcohol is gas-line antifreeze that contains
methyl alcohol. Read the label because some cheaper gas-line antifreeze
contains isopropyl alcohol. The use of isopropyl alcohol, including rubbing
alcohol, will cause the stove to smoke and make your windscreen and pot black.
Results
Alcohol
absorbs water from the air readily so always store alcohol fuel in a sealed
container. The stove quickly heats to temperatures that will cause burns so
only adjust the temperature ring when the stove has cooled.
With the
simmer top removed and the temperature ring adjusted for maximum air input, the
Turbo Cat II stove boils 2 cups of cold tap water in approximately 4 minutes 30
seconds. This is with a 6" black Teflon coated aluminum pot, lid, the
windscreen shown above, and a stove to pot distance of 2-1/2". With this
configuration, one tablespoon of fresh denatured alcohol burns approximately 6
minutes. These times are recorded from when the stove is lit until an audible
boil begins.
If the
temperature ring is adjusted to close the input air holes and the simmer top is
placed on the stove, a tablespoon of denatured alcohol will burn more than 30
minutes.
If your high
temperature results differ, verify that the distance between the pot and the
windscreen is approximately ¼” and that at least 1” of the pot is covered by
the windscreen. Also, verify that the insulation is 3/4" below the center
of the stove and at least ½" below the sidewall holes around the
perimeter. If problems continue, check the color of the stove flame at night.
It should be blue as shown in the above photograph with no or very little
yellow color. If the flame color is incorrect, try adding another hole or two
in the inner can. The soda can is very thin and sharp object can be used
to easily poke a hole through the inner can between the existing holes. If the
flame is blue, experiment with changing the stove to pot distance ¼” at a time.
This can be accomplished by placing the stove or windscreen on spacers such as
steel hex-nuts.
Warning and Disclaimer:
All of the
above information is considered experimental and unproved. If you decide to
construct a stove or use any of the information contained in this document, you
do so entirely at your own risk. If you build or experiment with an alcohol
stove, I strongly recommend you test your stove in a safe test environment and
take all precautions possible to protect life and property should something
unexpected happen.
John Bednar,
email:k3ct @ verizon.net
Revision
Date: March 7, 2008