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.

 

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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.

 

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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.

 

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The inside of the stove is made from a soda can bottom cut to a height of 1-3/8". Mark the can with a marker then carefully rough cut the can ¼" from the line with a scissors. Then re-cut the can to the final height. A 3oz cat food can may be used; however, the heavy ring at the top of the can will have to be removed so that the bottom cover can be epoxied to the can. This will be more difficult than cutting a soda can to the proper height.

 

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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.

 

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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.

 

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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.

 

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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.

 

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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 9 o’clock. Space the remaining four holes 2” apart. The set of holes on either side of the tabs will not be 2” apart.

 

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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.

 

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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).

 

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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.

 

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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.  

 

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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. 

 

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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.

 

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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.

 

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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