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Slimming the classic Trangia
Boiling away on the left is a lightened Trangia. The frying pan/pot lid has been replaced with a flattened heavy aluminium foil pie dish. One pot has been left at home, and that incredible brass meths burner lives in a new housing that packs flat into a fraction of the space. This slimming campaign has cut the total weight from 861 grams to 440 grams. If you prepare haute cuisine camped in gale force winds I suggest you stick with the original, but if camp cooking is mostly reheating, plus warming water for washing, the modified device does a good job. The new stove does need screening for gale-force cooking, but unlike the original can be pegged-down to reduce kicking accidents at night. I will try and explain how the new stove housing fits together, and then go into the construction in detail. If you are able, or willing to learn, to tap threads, and can use tinsnips, drills, files and a hacksaw there is no advanced metalworking, but some slow, careful work is required. I built the first (and only) slimmed Trangia in a full day and a half.
Taking off the cooking pot shows the familiar burner. It drops as before through a hole in a flat plate, but this time the flat plate has four legs to stand on. The legs continue above the plate, and four rectangular aluminium pieces drop onto the extended legs to form the square flame housing. The threaded ends to the extended legs are the right length and spacing to correctly locate the cooking pot on the housing and stop it sliding around. The flame housing rests on the four legs with a deliberate clearance between the bottom edge and the flat plate to admit air for the flame while optimising wind resistance. A similar gap is provided between the top of the flame housing and the cooking pot to let combustion products out. This gap is made with four short stubs each in the middle of a housing plate, and the pot rests on these stubs. The only modification to the Trangia as supplied is to take the combined low speed restrictor and snuffer provided, and drill out the rivet fixing so the snuffing disc can be removed. The new housing is too small for the opened snuffing disc to remain, so a small light (washed) aluminium cat-food can is carried to use as a snuffer.
One of the advantages of the new housing is that you can look in between the cooking pot and the housing corners to see what the flame is doing. A normal Trangia with the low speed restrictor installed starts so very slowly, but later seems to be boiling your pot much more vigorously than you might expect. You can now see the flame does start out very small, but as the heat warms the burner pot the evaporation rate of the meths and the consequent flame height both increase. By the time one-third of the burner fuel has been used the flame stabilises. There is an efficient transfer of heat from the flame to the entire underside of the pot, but no wasted heat can be felt flowing up the cooking pot sides. I have run the burner, with restrictor fitted, starting over-full with meths, and boiling water continuously until the burner is empty. There is no sign of flame 'runaway' or overheating of the burner pot. Outside in fairly windy conditions and about 12 degrees Celsius, the flame housing was just over 100 deg C, and I would guess the burner plate was at about 55 or 60 deg C.
The normal Trangia housing shrouds the sides of the cooking pot as well, allowing the 'fireball' from a full-throttle burner to be fully utilised. With some misgivings I ran the burner from over-full to empty, boiling water as before, at full-throttle with the restrictor removed. The water boiled much faster, as you would expect, but flames were coming out of the housing and wrapping round the pot much like many camp stoves with the wick turned up. The aluminium flame housing plates, with the flames in contact for a good deal of the time, ran sufficiently hotter to clear some of the light soot layer that had deposited on them during the long restrictor run. When the run was over the cool housing plates were still shiny, the short pot supports were fine, and there was no sign of bending or distortion. The flame housing plates at full-throttle obviously get hot, but there is enough flame around the area to warn you that touching them would be stupid. The burner plate was 'quickly touchable' which puts its peak temperature at around 80 deg C, or almost exactly the boiling point of meths. This temperature is well within the permissible range for the two nylon peg-down loops mounted on the burner plate.
With some surprise then, I can use my modified stove at full-throttle provided there is fuel available to deal with the increased thirst. Just looking at the stove running like this would suggest the original Trangia housing wastes less of the heat, but I have not done measurements. The ability to hot-run like this has very little to do with the brilliance of my design, and much to do with a very clever Trangia burner.
This is the cat-food tin snuffer. It lives over the burner cap when packed, so does not waste space. The increased height makes it easier to use than the original snuffer/restrictor, since it keeps your fingers farther away from the hot bits. The flame housing is air-spaced from the flat plate holding the burner, so the flat plate runs at a significantly lower temperature than the flame housing.
Once the four sides that make up the flame housing have been left to cool for a minute or two and lifted off, the four upper legs can be seen. The upper legs have the visible lengths of screw thread, and also each has a shorter invisible length of screw thread that is pushed through the hole in the flat plate and hand-screwed into the lower leg. Cooker assembly is thus a matter of screwing four upper legs into the lower legs through the flat plate, and then dropping the four housing plates on top so the upper screw threads go through the hole pair on each housing plate. Assembly is both quick, and easily possible by feel in the dark.
There is a very minor modification to the Trangia cooking pot handle. Two small lumps of aluminium are cut off the very end of the larger (top) part of the handle and show as the 'rough bits' in the photo. This mod allows the handle to be reversed so the hand is holding the end usually used to pick up the cooking pot. The two handle ends can then be brought together to pick up the heavy foil cooking pot cover by the rim. You can always knock this light top off, or whip it off by hand trying to avoid the steam, but if you are keeping a regular eye on cooking pot contents this is much safer and easier. You save a whole gram in aluminium weight as well!
This close-up of one of the four cooker legs concludes the description. The longer upper leg threaded section is pushed through one of the flame housing plates at the left end, but at the right end the hollow threaded lower leg is still in packed position screwed onto the shorter thread of the upper leg.
Since the slimming process finished, the now unused portions of the Trangia have gathered dust at home. If I need to use them again, I will also have to include the cat-food can snuffer since the disc has been removed from the burner restrictor. One of the least-loved habits of the original Trangia is that of melting its way down into the snow during winter cooking. I have made 'snow legs' for the modified cooker, and will add these to the account as soon as they have been field tested. As I write, a decent snowfall is shaping up on the mountains.
Disclaimer:
These modifications have not been submitted to, or authorised by, the makers of the Trangia. Breck Bowles, and Breck Bowles Development, disclaim liability for accidents arising during the manufacture or use of this modified Trangia cooker. As with any modifications to any mass-produced device, the person modifying the device must personally accept any risks involved.
Construction details
The actual Trangia modified was a 'classic Trangia' bought new between fifteen and twenty years ago. Both large and small models were sold at the time, and I have one of each. I bought the small one after finding it impossible to make space for the large one in my camp gear. The flame housing sizes are quoted for the small one. Trangia cooking pots come in stacked sets of two. The stacked set for the small cooker comprises inner and outer pots. The outer pot (wider and shorter than the inner pot) has an internal rim diameter of 136 millimetres, a height of 70 millimetres and an external base diameter of roughly 118 millimetres. The inner or outer pot will each fit on the flame housing with dimensions as given, but of course there is a little more slack space with the inner pot. All dimensions will be given in millimetres (mm) and there are 25.4 mm to the inch.
Customising
It is likely that either you will want the modified cooker to take a non-standard cooking pot, or the dimensions of a modern Trangia, if such a device exists, have altered. There is no alternative, if you are customising, to understanding how and why the cooking pot fits on the flame housing. As you can see from the water-boiling photo, the threaded upper ends of the support legs come right up the side of the cooking pot, with only a mm or two clearance between them and the pot side. If these high ends are not used, the pot will stand on the flame housing as on a normal gas stove. Any sideways knock with a foot will cause the pot to slide off, tip over and no doubt scald the foot as well as losing the dinner. The high ends and close fit are thus essential for safety, and combined with pegging down the stove will avoid many common camp cooking accidents.
The high ends stick out 22 mm from the upper support legs, but the effective height is reduced by about 3 mm for the combined thickness of the overlapping flame housing plates, and 4 mm for the short pot support stubs. The net height is thus 15 mm, and this is the figure to use in your clearance tests. On a sheet of paper draw a circle with a compass, with the centre clearly marked, a little larger than the base of your cooking pot. Stand the pot centrally within the circle, then slide up a vertical 15mm high matchstick until it nearly touches the side of the pot. Mark on the paper the base of the matchstick, then remove the pot and draw a straight line through the centre of the circle and your matchstick mark, extending it on the opposite side of the circle to the matchstick. Put the pot carefully back on the paper and slide the matchstick up to the pot again along the line you have drawn on the opposite side of the circle. When it nearly touches again, mark the position again. The two marked points on opposite sides of the pot are the same distance apart as your support legs should be when the job is finished. Draw another line through the centre of the circle at right angles to the first extending on both sides of the circle, replace the pot and mark the matchstick contact locations for this line. This should give you four points which when joined up should make a square. If it is too far out, do it all again. If this method does not appeal, and you have a six inch vernier calliper and know how to drive it, you can do a diagonal clearance measurement in thirty seconds.
Measure accurately the four distances between the four points. They will not be the same, but they should be close. The average distance will be your required figure for support leg spacing, and will have to be right to within about 2 mm. Before starting precise metalwork, it is worthwhile drawing an accurate square with this spacing dimension on thick flat card from a cardboard carton, or expanded polystyrene sheet. Drill or spike a hole right on each corner of the square, force a matchstick into each of the four holes, and trim them to 15 mm above the cardboard. Stand your pot (or pots) on your cardboard 'cooker' and make sure the matchsticks are all one or two mm away from the pot side. If they are not, adjust the square dimension until they are. When you have recorded the support leg spacing for your own pot or pots, remember the figures quoted subsequently for the length of each flame housing plate, and the dimensions of the flat plate that holds the burner will all have to be altered by you to fit your particular support leg spacing.
Making
The standard spacing between support leg centres is 96 mm. If you are going to vary this you will have to read and understand the 'customising' section above. Drilling, cutting and bending thin aluminium plate is pretty easy, so I will cover the making of the support legs first. Note the leg heights are standard, whether you are customising the flame housing size for a different cooking pot or not.
Look back at the enlarged support leg photo if needed. Both the upper and lower legs are made from aluminium with a tapped thread inside, and the upper leg has long threaded screws tightened into the two ends until both screws jam. The top thread is then cut off and smoothed to 22 mm length and the lower thread similarly treated to about 15 mm length. The 'engineering solution' to making the legs is to use solid aluminium rod, mount it in the lathe and drill it out to the right diameter to put in the thread-cutting tap you require. Not many of us have lathes these days, so it is easier to find some small size aluminium tubing, then find a thread-cutting tap that is a reasonable size for the internal diameter of the tube, so no hole alteration is required. Once you have cut the threads, you then find a specialist nut and bolt supplier (not your local hardware shop) who will have long setscrews available in this thread. The diameter of the finished support legs will thus vary according to what you can find, but this will not affect the running of the cooker. Large diameter support legs weigh more of course.
The tubing I found is pretty well the minimum diameter. The external diameter is 6 mm (close to 1/4 inch) and the internal diameter 3.75 mm. I found although the internal hole was really on the large side of ideal, a metric M4 tap cut enough thread to be usable. Keep in mind the only screwed-up joint has 15 mm of thread engaged, and is tightened by hand. Since the tap was taking out so little metal, I was able to use a non-taper plug tap, which wound in easily by hand while the tubing length being tapped was held in the chuck of an unpowered electric drill. I tapped both ends of the upper support length tube up to the full length of the tap. When I tightened in the long M4 setscrews, I found there was so little metal removed by the tap, that when the setscrew reached the end of the threaded depth, resistance to turning increased, but the setscrew kept on going forming its own thread in the bare tube. Locking the setscrews was accomplished by screwing them in equal amounts until they met in the middle. One was then turned hard against the end of the other, and the thread assembly locked perfectly. All that had to be done was to cut and finish the threaded ends to 22mm and 15 mm respectively. The lower legs were made from the same tubing and similarly tapped both ends. For a luxury conversion, the lower legs could well be made of larger diameter solid aluminium rod, drilled the right size (3 mm) about an inch deep from just one end, leaving the rest solid. This could be then taper and plug-tapped to form a more positive thread with a better engagement and feel. First find your lathe!
The upper and lower legs are cut a mm or two over length from whatever tubing you have found using a fine-tooth hacksaw. The tubing is filed almost to length, the ends being squared off by 'eye' at the same time. Finally the tubes are spun in an electric drill chuck and a file lightly applied to the tubing end to make it look as if it has been turned rather than hacked off. Both ends of each tube length are done in this way. All four upper legs and all four lower legs are the same length, which is 38 mm. Aim at matching the legs to a fifth or even a tenth of a mm in length, and your finished stove will always stand square on a flat table, as well as assembling easily and looking good. Once you have the eight matched lengths, cut the threads inside them as detailed above. Select four for the upper legs, and insert and cut off the threaded sections also as above. Your four support legs are completed, and will assemble as in the photo.
Engineering metalwork
Most of us can draw a square on a sheet of metal, and drill four holes at the corner points of that square. It is simple to clamp the metal sheet on top of a second sheet, and drill the four holes through to make a second hole set, that perfectly aligns with the first set. A decent sheet metal engineer can take care while doing so, and produce two sets of four holes which align perfectly with each other, no matter whether the second sheet is as drilled beneath the first, rotated 90 or 180 degrees, or even flipped over. This level of precision is not learned overnight (try it yourself!) but it can be done, with an electric drill and hand tools. A well-made flame housing requires precision approaching this standard, so be prepared to work slowly and carefully. You will need a vice and something to bolt it to, a handyman square of the variety with a sliding steel rule and a cast-iron body, a metal scriber, which is often found pushed into a hole in the handyman square body, and a drilling centre punch plus a hammer to hit it. Useful extras are a one foot stainless engineering steel rule, a six inch steel engineering vernier calliper, and a magnifying glass or head-mounted flip-down magnifiers. A kindly engineer, if there are any left, will show you how to read a vernier. If you are made of money you can buy a digital vernier, but a permaflate airbed would be a better investment.
The flame housing
The four housing plates are made from thin gauge aluminium 90 degree angle extrusion. 'Standard thin' in Australia is 1.6 mm thick. The one meter length in stock was of 25 mm x 50 mm dimensions, which was generously oversized in both directions. This material is cheap, waste is allowed, and it is much easier to get the tricky holes drilled in an oversize and overlength piece. Once the holes are in the right place you can carefully cut down the excess sheet round them until you have a housing plate of the right size.
You have seen this photo before. The correct position of the hole in what will become a housing plate depends on the diameter tube you have used for the support legs, and the size of the hole is the smallest that your support leg threaded section will easily push through. The aluminium tube rests flat on the inside wide section of the angle, and the hole is drilled in the narrow section just above the wide section, so as you push the support leg forwards, the threaded section passes freely through the hole. You can drill an undersized hole and 'move it around' using a needle file until it fits. I took a drill of the right clearance for my thread section, and just free-drilled a series of guessed holes along a length of extrusion until I had one that was correctly aligned for the support leg. Once I had a 'master hole' I clamped a section of thicker 90 degree extrusion behind it, and carefully drilled through the master hole and into the thicker material, to make a drilling guide that would then allow me to drill any number of holes in the right position.
Using a drilling guide if it suits you, drill a pair of holes in the extrusion with the centres 96 mm apart. Note that if you are customising for your own cooking pot, this distance will probably not be 96 mm. After checking the centre to centre dimension on your drilled holes cut off the section with the two holes from the rest of the extension. Make a rough cut, allowing say 20 mm of length on the outside of each of the two holes for later trimming to size. Take the burrs on the rough cuts off with a file. Clamp the cut-off extrusion back to back (or mirror image) onto the next length of extrusion, making sure the edges and flats align correctly. You can now drill through the first set of two spaced holes, to make an identical set in the next length of extrusion. Cut off the next set of holes allowing extra for later trimming, and repeat twice over, always drilling through the first set you made. You will now have four extrusion sections, with identically spaced holes in each and spare metal to allow for trimming to size.
The photo shows, on careful examination, that the four housing plates are not all the same, but come in two pairs. These will be called the first pair and the second pair. The first pair drop on opposite sets of support legs first, and form two parallel sides to the flame housing. The second pair then drop on to complete the housing. In the photo the first pair are close to horizontal on the Web page, and the second pair are close to vertical. The second pair overlap the edges of the first pair, so they must be longer, and since they rest on the tops of the first pair, they must be wider than the first pair in order that the spacing between the bottom of the flame housing and the flat plate is the same on all four sides. Read the above until it makes sense.
You can also see, but not easily, that there are differences in the short stubs that support the cooking pot. Because the second pair sit on the first pair, the stubs fitted to the second pair must be shorter than the stubs fitted to the first pair in order that the tops of the four stubs are at the same level. This stops the cooking pot rocking on the two highest stubs. This difference in stub height, by the way, makes the housing easy to assemble in the dark, since the longer stubs on the first pair can be found by feel.
If your support legs do not differ much from 6 mm diameter, and the plate thickness is close to 1.5 mm, the first pair of plates measure up at 104 mm long if you are not customising, and the second pair at 108 mm. Larger diameter support legs mean a bit more length is needed. Cut the housing sides to length, taking care and using your square and scriber, getting the holes symmetrical inside the trimmed lengths. It is worth leaving a mm or two extra to be removed after final assembly, since taking it off is always easier than putting it back on. If plate thickness is close to 1.5 mm, the external width of the first pair of plates is 37 mm, and the second pair 38.5 mm. These widths can be scribed on and the plates cut to size. This measurement will not change if you are customising. When the housing is assembled on the yet to be built base plate, this establishes a bottom gap all the way round of about 2 mm. It is easier to widen the gap than to narrow it.
The top width of the four housing plates is non-critical, but looks best when the holes for the support leg threads sit in the centre of the width when viewed from the top as seen in the photo. On mine this corresponds to an external width of 10 mm, but if your support legs are larger in diameter, maintaining central location will require the tops to be wider. Scribe and cut the tops to width. The short stub locations are non-critical, and I suggest these are left until after final assembly. This completes housing plate work for the moment.
The burner base plate
Aluminium sheet is available in much better tempers than the soggy stuff used for extrusion, and this allowed me to make the base from 1.2 mm sheet. The edges of the base are turned down to add rigidity, improve looks and enforce flatness in the contained sheet. Snip out or start with a considerably larger square than you need, since the critical holes will be drilled first, and then the rest of the sheet will be snipped to acccurate proportions around wherever the holes have ended up. If the sheet is not flat, thump it with a rubber mallet until it is. The hole marking method assumes all the flame housing plates have identical hole positioning and spacing.
The first move is yours. Drill one of the four corner holes in the aluminium sheet as close as possible to where you think it should go after looking at the above photo, and considering if you are customising or not. If the hole is less than 25 mm in from an edge, you may run out of metal. If your sheet is pretty small and the hole is too close to the sheet centre, you may run out of metal on the other side. Unless you are customising for a big cooking pot I would suggest a minimum sheet size of 180 mm square, and a first hole in one corner about 30 mm from each of the corner edges. The hole size is the same as the pair in each flame housing plate. Take one short setscrew of the same thread as you have used in the support legs (M4 in my case) plus a nut, and bolt down one hole of a flame housing plate onto your drilled hole. When the nut is half-tight push the plate until it runs parallel by 'eye' to the edge of the sheet. Tighten the nut, clamp near the other hole on the housing plate to hold it firmly to the sheet, and drill through the second hole into the sheet. Unscrew the holding nut and take off the plate. You should have two of the four support leg holes, as shown in the last photo, drilled in the sheet.
Scribe a line on the sheet using a steel rule between the centres of your two drilled holes, then scribe another line through the centre of one of those drilled holes at right angles to the first line. Bolt the housing plate back on to the hole with two scribed lines running through it, and swivel the plate until it is at right angles to its previous location. You should be able to see your second scribed line by looking through the second hole in the plate. When the line runs exactly through the centre of the second hole, by 'eye', tighten down the nut, clamp the plate and drill the third hole of the set through the vacant plate hole into the sheet. This gives you three holes out of four, but the last hole is more tricky. Minor deviations from a right angle are permissible for the housing, but the four hole-to- hole spacings must be the same. Repeating the right angle method will produce errors.
For the last hole, you need to make two flat strips of aluminium a little longer than the flame housing plates. Anything over an inch wide is fine, and they can be made from odd lumps of housing plate extrusion. Clamp a housing plate any old how onto the flat strip, and drill through both holes, so the size and spacing of the holes are transferred to the flat strip. Repeat to make a second hole pair on the second strip. File off any drilling burrs. Returning to the main sheet, we have three drilled holes. If you drew a line between hole 1 and hole 3, it would pass through the centre of the meths burner. These are the holes used for the next step. Bolt one hole of a strip fairly firmly into hole 1, and one hole of the second strip similarly into hole 3. You can lift the second strip above the sheet with a couple of washers if you are being exacting. Swivel the free ends of both strips until one crosses the other, and the two second holes align. Put your drill through both second holes at once and drill the fourth hole into the sheet. Check that if you swing the two strips back over the other side of the sheet, the two holes should meet precisely over sheet hole 2. Remove the strips from the sheet. You should be able to bolt a flame housing plate down between any pair of the four holes on the burner base. If they won't quite align it is probably OK, but if any are way out, give up or start again with a new sheet, checking your housing plate hole spacings as well.
Scribe ruled lines between hole 1, and hole 3 and also between hole 2 and hole 4 on the sheet. These lines will cross in the middle of the burner hole. Punch mark this middle point for later use. Scribe lines parallel to the lines joining holes 1 and 2 etc, but about 20 mm farther out towards the edge of the sheet. These lines will define the larger square holding all the metal sheet that the burner plate will use. Tinsnips are now run along these wider lines to cut off the excess on all sides, and the sheet is now bent back flat if needed. I cut 45 degree chamfers about 20 mm long with the tinsnips, to help appearance and the bending process, on each corner, but these are not compulsory. Clamp a block of wood in the vice shorter than the sides of your square sheet, and with a hard rubber tentpeg mallet just fold down the outer 10 mm of each side. The bend can be rough and radiused, does not have to go the full 90 degrees, and I just held the sheet with one hand and tapped the edge over the block with the other. It took all of five minutes. The result is a very rigid sheet as shown in the last photo, perfectly flat inside the four bends.
Now the sheet is rigid, you can make the central hole for the burner. A clearance hole for my Trangia burner measured out at 70 mm diameter. In this case set any handy compass for 35 mm radius and locate its point in your central punch mark before drawing the circle. Pencil will show enough on aluminium, or you can use pointed dividers to scratch a circle, if you have them. Cut round just inside the circle with a coping saw, fretsaw, piercing saw, tension file or whatever else you use for curve cuts in aluminium. The hardest job is finding a tooth size fine enough to cut 1.2 mm aluminium, so I used a tension file (the Abrafile) but this is not well known outside England. Once your hole is cut you can open it out with a half-round file until it is smooth and the Trangia burner drops freely inside.
Assembly
Unscrew a lower leg from the threaded upper, push the short thread of the two available on the upper through one of the four small holes in the burner plate from the top, and screw the lower leg on again, getting used to the feel of the properly engaging thread to avoid crossing it. I have not damaged a thread yet. The lower leg is screwed on half-tight to still allow the assembled support leg to wiggle a little. Repeat for the other three legs. Stand the four-legged base on the table, select the first pair of flame housing plates and drop one on each pair of support legs. In practice one hole is dropped over a thread, and the other leg is wiggled gently until it goes into the second hole. Once the first pair is on the second pair can be dropped on to complete the flame housing. If the holes are really too tight on the threads, they can be opened up to the next drill size, but don't overdo it. If you are being thorough the lower legs can now be tightened. The short stubs have not yet been installed, but you can lower your cooking pot onto the flame housing to check the fit is about right. If you put on the first pair of housing plates and they are too long for the second pair to fit over them, trim off the excess as required. Trimming the second pair is only cosmetic, as extra length does not obstruct assembly. Remove the cooking pot. Find or beg a small aluminium cat-food tin. These USA-made 'treats for pampered moggies' are widely-available, and come in ultra-light seamless aluminium cans. A washed can makes an ideal burner snuffer. Finally if all works, drill out the rivet fixing in the Trangia snuffer/slow burning device before removing the pivoting disc. Drop the device over the burner, splash in some meths and light up. You cannot heat the cooking pot yet, so extinguish the flame a couple of minutes later with the new snuffer.
The short stubs
These cooking pot supports are non-critical as to placement. The cooking pot stands 4 mm above the second pair of flame housing plates, and 5.5 mm above the first pair, so these are the respective heights of the two sets of short stubs. My stubs are made from the same M4 setscrews as the rest of the threads in the housing. I drilled a third hole in each housing plate in the middle of each top (see snuffer photo) but made sure they were far enough out from the angle of the extrusion to allow room for the heads of the setscrews, which were pushed up from underneath. On top enough stainless steel washers were piled up (one for the second pair stub, and three for the first pair stub) to set the height, and a hex nut was tightened down on top before the excess thread length was cut off with a fine tooth junior hacksaw. If these values make your cooking pot rock, alter the offending pair of stubs.
The anchor points
These 'afterthoughts' have worked very well. I just bodged a hole through on the lip side of the bend about half-way down two sides of the burner plate, and inserted a partially-closed nylon 'cable tie' through each. A loop of nylon cord will do instead. The burner plate never gets above 80 deg C, so these loops will not melt out, and if they do, you want to know about it! The cable ties could be melted by a large meths spillage fire, but are replaced very easily. Wire loops would be most unpleasant and get in the way of everything. Fine metal chain would probably be the best, but life's too short. You could get extreme stability with four loops and pegs rather than two, but two are really quite adequate
Final running
With the short stubs installed, reassemble the cooker as before. Make sure the cooking pot is standing on the stubs, shortening the upwards threads on the top of the support legs if they are touching the pot and stopping it resting where it should. Put meths in the burner, the restrictor over the burner, and have some water ready in the cooking pot. Light up the burner, drop on the cooking pot with its pie-dish cover, and watch her go. Once you are confident with this, you can try a full-throttle run, but not indoors or close to your tent.
Comments
This project took much longer to photograph and write up than it did to make and test. I made it, and it simply worked first time indoors, out, and on genuine camping trips. I thought the burner might be warming a little more than it does in the normal Trangia housing, but I can find no evidence of this. This system is now part of my camp kit, and I shall be making up luxury, fully threaded support feet with the aid of an engineer and a lathe, as described in the text. With the restrictor in place over the burner, the pie dish cooking pot top can be replaced with my polypropylene breakfast cereal plate, which lifts on and off with the standard Trangia cooking pot handle. The edge of the plastic shows no sign of melting, and the improved insulation cuts the time required to boil water. I would not try this substitution running the burner at full-throttle.
Ongoing development and testing (1st August 2000)
The lightened cooker has melted snow and warmed water for washing on one trip. The aluminium lower legs were not screwing on as smoothly as they might have done, although they worked. On return I located a large supplier of brass tubing and managed to get some quarter-inch outer diameter, 1.5 mm wall thickness tube, which works out at an inner hole of 3 mm diameter. Tapping deep M4 threads in this correct dimension hole required patience and care. With a slight weight penalty I now have brass lower legs for the cooker, and these screw onto the upper legs smoothly and precisely.
I made up 'snow feet' for the cooker from 3/8 inch (about 10 mm) semi-rigid nylon compressed-air high pressure tubing. This has an internal diameter of just over 1/4 of an inch, and pushed loosely over the lower legs. Four 160 mm lengths were cut, the precise figure not being critical. This tubing comes in a roll, and the lengths were distinctly curved. I pushed the snow feet over the lower feet of the cooker, and then pushed the cooker housing and snow feet down into loose snow until the base of the meths burner was about half an inch above the snow. There was some flex in the snow feet due to the curvature of the legs, but the cooker stood extremely solidly above the snow like an offshore oil-rig on its supporting piles. I repeatedly melted snow and boiled water. The full water pot remained rock-solid during violent stirring and pushing. After much heating, not only was the cooker just where it started in the snow, but the snow that had been driven into the hollow snow feet during setting-up was unmelted. The 'snow feet' really do stop your cooker from working its way downwards. The total weight of all four snow feet is 29 grams.
On a still morning not long after dawn at about minus 10 Celsius, I had to use a dead leaf as a 'wick' to get the meths started. At full throttle (no restrictor) the stove melted snow in an exemplary fashion, and I could just shovel the snow into the cooking pot since excess dropping outside the pot did not fall into the normal large housing. I could not feel flame up the sides of the pot, and no heat was being wasted. Just out of bed at these temperatures one does not take the greatest of care. The cooker just ran, and did not threaten me once.
The only slight snag found was that if you tighten all four feet after assembly without watching the result, you may end up with a flame housing that is not square, but diamond-shaped (rhomboid). If you put a cooking pot down on this distorted housing, one pair of upper leg extensions will be too close together to let the pot down onto the support stubs, and it will rock. The answer is either to hold the housing square as you tighten the feet, or not bother to fully-tighten the feet. The cooker works just as well, and is equally stable, if the housing is left slack.
The conclusion so far I suppose, is that I may have to look for a buyer for one Trangia cooker external housing, looked after with great care for the last 25 years.
Breck Bowles
breck@permaflate.com |
