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Slimming the classic Trangia - the Trianglya

The trianglya is a triangular housing for the Trangia burner. The previous slimming project was square. Housing weight is down from 185 grams to 120 grams, and the dismantled housing is much smaller. Assembly time has gone from a few minutes for the previous version to fifteen seconds. Water-boiling tests in still air (the next section in the supplement has details) show boil time is down from 8 mins 30 seconds for the fully-shielded Trangia housing, to 6 mins 30 seconds. Fuel consumption during this test is slightly down, from 16 grams (Trangia) to around 15 grams (trianglya).

The previous section on the square version is worth skimming for the general design background and history of the project.

The new stand incorporates the circular hole supporting the Trangia burner into the bent metal of the three sides, rather than use a separate plate.

The old stand has 13 pieces, counting the 4 two-part legs as 8. Assembly takes a couple of minutes, and the leg parts are small enough to take some finding if dropped into leaf cover or long grass by mistake. The new stand has 6 pieces (three sides, three legs) and assembles in 15 seconds. The legs are large enough to be located if dropped. Small drop-in 'pot rests' have been added (see next section on testing, tuning and use). You are expected to lose a few of these, so carry a spare or two.

The stumpy legs of the new design are hollow. It you stand the cooker on snow or ice it will of course melt its way downwards, and I used 'snow feet', which are three short lengths of wooden 'dowel rod' pushed inside the legs, so the cooker rests on the insulating rods going into the snow. Finally it dawned on me that any time I was cooking on snow I carried a snow shovel. I laid the shovel flat on the snow , and stood the trianglya on the shovel face. End of problem. On the lathe, a minor change was made in the form of a chamfer on the bottom of the three legs, to reduce the area in contact with the snow shovel, further conserving heat. Unless you do not carry a shovel, 'snow feet' are now obsolete. With the increased stability of the new version, pegging down should not be required unless, heaven forbid, you are leading a school group or similar. Light chain lengths can be dropped over the exposed leg screws when the stand is assembled, and pegged out with tent pegs, if required.

You can see the unusual stability of a flat triangular support. The cooking-pot contains water, nothing was glued together, and gravity is functioning as usual. Note if the pot-rests are in use, stability drops to more normal values.

The new stand (right) packs down much more compactly than the old stand (left), and weighs 65 grams less. The Trangia burner and a well-heated cat-food tin snuffer are also shown. The snuffer has recently been trimmed with tinsnips to a 22 millimetre depth, saving a bit more space and weight.

Where's The Catch?

The old stand required basic, if careful metalwork. The new stand requires advanced metalwork, including precision bending, and the use of a lathe to turn and bore the three legs.

Many home-made camping gear projects demonstrate that if you combine minimal skills, minimal tools and minimal effort, what you make is likely to be of minimal use to anybody. I have read plenty of projects, and have never made up one. Perhaps all projects, including this one, are simply read for entertainment and 'background'.

I am tackling this unhappy situation in two ways. I will present enough detail for a skilled metalworker to make one up for himself (the sexist bias is deliberate). There may be some Trangia enthusiasts that would like to slim their baggage, but do not have the considerable gear required to make this project. I have made up a dedicated bending jig and an accurate template, and am quite happy to make a stand as described, and post it out to you. Price will be 50 Australian dollars (one Australian dollar currently buys 64 US cents). Overseas airmail/insurance costs 15 Australian dollars. Note that the Trangia burner is not cheap. You are responsible for providing the burner, and making sure it drops into a 71 millimetre hole. If there is demand, I will get a batch of shapes water-jet cut from aluminium sheet, and begin low-level production. E-mails to breck@permaflate.com

Supply update. There has been some demand, and I can normally supply built-up units from stock now.

Burner dimensions.

As far as I know, the standard Trangia burner has a tank external diameter of just under 70 millimetres. Above the tank is the support rim, the widest part of the burner, and this has a diameter of just over 75 millimetres. The burner stand as presented has an internal hole 71 millimetres in diameter, which allows the tank to drop through, and supports the burner at the rim. If your Trangia burner differs from these dimensions, I would be very glad to know.

The rest of this section covers making a trianglya, in detail. If making one is out of the question for you, it might be worth going straight to the next section on testing, tuning and use.

Design details

The idea of three folded aluminium pieces forming a triangle when bolted together via a hole at the end of each piece, is simple. The tops of the pieces are bent outwards, both to make them rigid and to generate a support surface for the cooking-pot or frying-pan. Under the top edges are rows of half-inch holes which vent flame. The Critical Temperature for tempered aluminium sheet is about 350 degrees Celsius (centigrade) and if this is exceeded for hours at a time the sheet loses its temper and reverts to the soft state. Maximum temperature at full burner operation, of the hottest parts of this design, is not much over 200 degrees Celsius, well below the Critical Temperature. Space is left at the three ends where the pieces meet, to provide extra flame vents at the top if a large frying-pan is used, while the lower part of the space admits air. The lower folded-in sections form the required 71 millimetre hole, but the hole is made with gaps, which become three lower air vents when the burner is inserted.

If you try (or visualise) bolting three internally-folded sections together, they will only do so symmetrically if one end of each piece is 'up' and the other is 'down'. This makes for the three top faces not being flat and parallel, and the same is true for the bottom faces. This will not do. Each internally folded section is split into a 'curve' section, which is part of the burner hole, and a 'tab' section.

The view above shows two unbolted sections facing each other, so both tabs are 'left' and both curved sections are 'right'. Looking carefully at the lower left edge view of the tab, you can see it is folded about one thickness of metal higher than the rest of the section. This is what I call a 'stepped fold'. This tricky job was done by milling out a shallow slot in the folding jig to take the tab. Once this was done all the stepped folds were consistent and repeatable. When the stepped folded sections were put together, all three tabs located above the plane of the curve sections, and both the burner hole and the three top faces were now flat and parallel. A device that looks and feels right is not always as simple as it appears.

Holes (1/8 inch or 3 mm) were now put in the 'right' place at each end of the three sections and the final assembly could be test-bolted together using M3 screws. It was relatively easy by filing and fiddling to knock up an assembly that fitted correctly 'one way round', but making an assembly that was symmetrical demanded significant measurement and calculation. Unless you want to mark which ends fit together, symmetry is essential for fast use in the field. Once the symmetry problem was solved, a template was made of the profile of the sheet, and also the centre locations of each drilled hole. The template is 135 millimetres wide.

To be precise, the above view should have the lower edge of the template accurately parallel to the bottom edge of the view. The photo has thus a small amount of geometric distortion, which you will have to correct for, if you want your template spot-on first time. Part of the Trangia burner is also shown.

Two of the drilled holes were made to align precisely with two machined pins which located the two halves of the bending jig together. In use an aluminium cut shape with holes drilled out is pushed onto the locating pins of one half of the bending jig, the second half of the jig is pushed on, and the jig held in a large offset vice while the top fold and the bottom stepped fold are done in one operation. The folds are the same every time, so the assembled stand is mechanically true.

The support legs

Two-part legs similar to the first version could have been used, but these had proved to be a little 'fiddly' in the field. I normally have deep reservations about devices held together with self-tapping screws, having encountered too many dreadful messes with stripped threads and/or screws aligned way off vertical. The tempered aluminium sheet is about 1.2 millimetres thick, so a small self-tapped hole was possible, but with not much margin for error.

The problem was resolved by using a truly massive (over 5mm OD) self-tapping screw thread, and forming it into the 3mm undersize hole in the tab of each section. Such an operation only generates a single-groove thread, but it is strong. The screws in the legs are only hand tightened on a half-inch diameter leg, so stripping of the thread is way beyond human strength. Forming a big thread like this into an undersize hole cannot be done by just winding a screw in - it goes all over the place. The tab had to be held down firmly on a bench drill press, while an oiled thread section firmly held in the chuck was wound down into it by hand operating the drill pulleys with the power turned off. This produced a perfect 'self-tapped' thread at right angles to the tab surface. The hole at the other end of each section was drilled out to clearance for the self-tapper, and no wider.

Support leg internals

The photo shows a completed leg, plus the self-tapping screws used inside it. Before the screw is inserted up the leg, the head must be turned down as shown so there is space for it to pass up the bore.

40 millimetre lengths of half-inch diameter aluminium bar were parted off using the lathe. Most of the inside of each length was bored out to a wall thickness of about 2 millimeters, leaving a short end section that was drilled out to allow the self-tapping thread used to 'chew' its way through the metal remaining. Long self-tappers had much of the head width removed on the lathe while still leaving the pozidriv screwdriver slot intact. Using a similar technique as threading the tab, a precision-located thread was formed inside the end of the leg before a turned-down head screw was pushed up the hollow leg and tightened. The result is machined hollow legs with immobile screw threads that nevertheless can be removed with a screwdriver in case replacement is required.

The snuffer

As with the first model, the housing body is not wide enough to take the restrictor/snuffer supplied with the Trangia burner, with the pivoting cover cap swung outwards. You must drill out the hollow rivet so the cap disc falls off. The restrictor then functions as usual, but you need to carry a snuffer in addition. The best snuffer is a small aluminium cat-food tin, of the type that holds 'tiny treats for pampered moggies'. Wash it out well and do not eat the contents. This size can fits over the burner cap and restrictor, so adds little to the bulk.

In conclusion, 65 grams more has been saved, and functionality has been improved over the first folding Trangia stand. This has however been done not by elegant, simple design, but by throwing engineering at the project. For this reason, although the new version will replace the old in my pack, I am not too pleased with it.

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Not using the snuffer

Dropping the snuffer on has always been a character-building adventure. Some customers in New Zealand wanted a system for putting the simmer ring onto the burner pot which was less risky. I laughed for a few seconds before conceding they had a point. It would have been impolite, but on e-mail no-one can hear you chuckle.

I bent up a thin aluminium strip about 0.8 mm thick or 1/32 inch. Giving it a slanted single folded back end allowed me to very easily pick up the simmer ring. Once it was on the end of the strip I could lower it over the flaring burner. It was quick and safe, and the folks in NZ were right. I now carry such a strip as a matter of course.

Once it was safe and simple to move from full flame to simmer, and back if necessary, it seemed logical to extinguish the burner from simmer rather than going full blast. I started as the following photo shows with a complex bend on the other end of the aluminium strip that could pick up the inverted screw cap of the burner, so I just slid it across the top of the fitted simmer ring to put the flame out. Picking up the screw cap edge was not simple, and neither was making the complex bend on the strip. Neither was needed. Once the flame is low, the cap can just be picked up in the fingers and slid upside-down to extinguish the burner. The new strip has made the cat-food tin snuffer superfluous.