I only took off 2 mm. The hottest point is slightly above the tip of a flame and only important when simmering. At max power output it's always hot enough to keep the vaporizing chamber working. The half roarer-half silent effect is easy to correct with a mixing tube. Start with 4 holes of 5 mm and increase by 0.5 mm until you get the desired result. Perfect air/fuel mix depends on jet and head sizes. My recommendations were based on a XGK X-G/S-G jet and a BD cap. juergen
Dikman, try brass the next time. Heat conduction differs in brass and steel. For steel you probably need to experiment more although I see you are indeed handy with a lathe so I do not see much of a problem. Ron
Ok, fitted a mixing tube with 4 x 6mm holes. Took a little while to get going, like you're all saying I suspect there's too much mass to heat up initially. Anyhow, it settled down and didn't look too bad, burning via the cap. I decided to increase the air hole size to 7.5mm, working on the principle that it should only draw in the air that it needs, as long as the holes are big enough not to cause a restriction. Fired it up again, and it looked good, burning nicely. I then stuck a saucepan of water on, to see how it heated. Started off ok, but after about 1 1/2 minutes it suddenly went into half roarer/half cap mode again! My gut feeling is that the cap is still sitting too high, but unless I grind down the fins even more (which I'm reluctant to do at the moment), it's going to require a new cap, specifically made for this burner. More thinking required! Ron, I have been contemplating using brass, but at the moment I'm using what's at hand - I'm not spending anything until I know exactly what I'm doing!! I'll probably use steel again, but next time make it considerably thinner all around.
I am sure this will work but you can test it first, get a thin washer that fits snugly on your fins touching the sides. Pop the cap on top and give it ago. Mine touches the sides, an added benefit is that when the burner cools it tightens around the cap and it wont fall off.
I reckon you're right and it would work. However, I'm part way through making a second cap, this time out of brass (from parts of an old mixer tap and plumbing fittings!). This should be closer to a BD cap in construction, with a wider base, so I'll be able to compare the two. Oh, I forgot to mention that when burning the flames tended towards yellowish at the tips, not the nice hot blue flames that you guys get in your photos (using shellite). Not enough air, do you think?
Hi dikman. First of all you should consider the following: If the air intake holes are too small you'll get mostly yellow flames. Too large and you'll get flame lift off. Yellow flames at the tips of the flames occur when running a stove without a pot. But if you get sort of a flash back WITH a mixing tube then something totally different went wrong. I suppose it's your head design. It obviously doesn't allow the gas to exhaust at higher pressure which you get with larger air intake holes. Or secondly, it could be the overall pressure from your fuel bottle. With silent heads you usually need less pressure than with a roarer. I would suggest trying the following: Get back to 5.5 mm holes and pump up to 20 strokes max for a full fuel bottle. And use a XGK X-G jet. Then you are close to my design except for the head. The best way of course would be to obtain a BD cap And don't shorten the fins any further. BD caps plus mixing tube do work even without shortening the fins. Best juergen
Thanks for the advice, juergen. You may be right about my cap design (probably are ), so as per my last post I'm in the process of making a new cap as close to the BD design as I can get it (from brass, this time).
I did my modifications step by step. First I was experimenting with jet sizes, then I tried a head from a gassie to see if/how it works. After that I switched to a standard inner/outer cap from a 111 and tried out various mixing tube dimensions. Eventually came BD caps and shorter fins. It's not difficult at all, but you need some patience and only change one parameter at a time. Best juergen
Version 2, this time out of brass. It's as close to a BD as I could get. It's a very close fit against the sides of the bell, and seems to work ok. It's pretty quiet, and certainly puts out some heat (I could see lots of heat shimmer going up around the sides of the saucepan). My original intention was to extend the inner tube closer to the jet - hence the long tube in the photo - but muggins here didn't measure the gap between the fins first, and it wouldn't fit so I had to cut it off flush!
The outer cap looks pretty good now, but the inner still has too much mass. What I can't see from the pic is the distance/clearance between inner and outer cap. The mixing tube should indeed fit between the fins Could you try to make an inner cap with less mass and solder the parts together on a base plate like Gary does? Best juergen
Based on the discolored pot supports, it looks like you got a good flame. But, it sure would be nice to see the rascal burning...... Flame! Flame! We want flame! Pleeeease? Cheers, Gary
Sorry guys, the photo isn't clear but the inner part is hollow (not a solid piece), as per BD's design. I tried it out last night as it got dark, and it looked pretty good . I'll have to try a photo in the dark sometime. It still took quite a while for it to actually start burning properly, but that is obviously due to the peculiar pre-heat system this stove uses. But I'm happy.
Ok, that looks much better now. But since you have cut the tube off flush you should use kind of a baseplate. Otherwise you get a somehow strange gas flow. Since the fins are nearly out of function with a silent head heating up the vaporizing chamber just takes as long as with an Omnifuel without heat fins. If I preheat with 2 ml of meth it then takes about 20 seconds to get the head up to working temperature. juergen
I really must learn to explain things better . Juergen, there is a baseplate on it, resting flush with the sides of the bell. The previous photo was taken before final assembly of the baseplate.
I've tried to take some flame photos, but I need to work on this a bit! The first one was with a flash (doh!) the second one I turned the flash off, but the autofocus was having issues with the flames (the rest of the photos didn't work out). I might have to try again with my other camera - it's not quite as automatic. Btw, how do you guys take such photos? Any secrets I should know?
I usually take photos in the basement, a slightly dark floor. No flash, quiet hand or tripod. That's all. juergen
Very big congratulations! That looks great! You are well on your way to BlueThumb Master Cap Builder. I hope you'll continue your experiments and building of caps. Thanks for sharing your voyage and pictures with us. Cheers, Gary
High praise indeed, coming from the acknowledged Master of the Cap . (I guess that makes me an apprentice novice, J. G. (junior grade))? Anyhow, one last thing to wrap up this little experiment. I Found a large washer that fitted nicely in the bell, and sat my original steel cap on it - lo and behold, it worked. So I desoldered the cap (again), chucked it in the lathe and took off a few thou. from the bottom, then re-soldered the bottom bit on and did likewise, thinning it down as much as I could. I then soldered the cap to the large washer, which then sat reasonably low in the bell. It takes a minute or so warming up to get up to heat, but once it's going it actually seems to work better than the brass versions, bearing in mind that it has 5 rows of holes, but with 3 gaps spaced around it, compared to the "standard" 4 rows of holes in the brass ones. It also seems to run better at simmering heat - I don't know why it should be different, but it is. So I now have 3 caps and one stove (!), but hopefully my other one should arrive soon. All in all, it's been a steep learning curve, but I'm . (What a great site).
Well, 2nd J.G. at least Simmering behavior depends on the right mix of gas/air, velocity and jet size/head design. It takes some testing to get a perfect combination working over the complete range of control. I kept jet size and head constant and only changed the air inlet holes of the mixing tube. When I had the right dimensions I worked on the head: No gaps between rows to avoid flame lift off. Then increasing the number of rows to 5 and 6. In fact it was of course Gary who provided the different head versions! 4+5 rows work perfectly without changing anything else. For a 6-row-design I need larger air intake holes. But in the end I found the 4+5 row versions to be more than sufficient in terms of power/heat output. Nevertheless, a 6-row head is just awesome at full power Best juergen
