Framebuilders - Velonomad, MAPP help
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10-18-08, 09:12 PM
I have been digging in the archives and ran across a thread where you posted some fillets that you did using MAPP. The pictures are understandably no longer linked being from 05 and all. Would you happen to still have them?
I have a Bernz O Matic MAPP/o2 kit that I am wanting to use to do a fillet brazed frame. Any advice?
My feeling about that since I tried the MAPP route also, is that if you have O2 you can get by fine with propane, and it is cleaner. If you are trying to get by, as is barely possible, without O2, then MAPP is better, you will not get proper brazed joints, but they may well be good enough. You can do it with propane if you have enough torches... I have seen production facilities that are set up that way Multiple head, hearth type set-ups, and brass donuts and flux in the tubes. Without O2 I used silver.
The normal quibble against those O2 kits is that the O2 cost mounts up. But really, if you just want to do one, I don't see the problem. Particularly since you already have the O2 set... If you are trying to get into framebuilding I would hold off till you can justify the right kit. I bet some of the "real" rigs will come up for sale pretty regularly on ebay and craigslist in the current environment. I'm not too sure what perfection looks like since every system has it's flaws. OA is good but it is almost too hot, you just need to figure out the system you have.
10-19-08, 02:34 AM
Yeah, I may or may not have access to an OA set up... I need to make a call. If I can I will use that. I hear you loud and clear on the 1lb bottles of o2 that stuff doesn't last long. When using only MAPP, what do you mean by not proper brazed joint?
Ultimately I want to build multiple frames, and maybe build for others (I can dream right) I will have an OA or OP set up in the future, but for now with my students buget I will have to make due with what is available to me.
Thanks for your input, you have answered my questions in the past and as alway you are very helpful.
10-19-08, 01:12 PM
I can't imagine using MAPP. I tried to silver braze some thin bandsaw blade material with MAPP, and I didn't have enough heat. You want too much heat, not too little.
10-19-08, 02:40 PM
I have silver brazed on cable stops with o2 MAPP it does work and it really doesnt take long to get think bike tubes glowing (read, to hot for silver.)
10-19-08, 05:13 PM
Sorry, I didn't notice the O2 part until I responded twice. I don't see any problem, it should be plenty hot enough.
10-19-08, 06:00 PM
The pictures you are asking about are on another computer which is buried in a warehouse for the next few months.
The mapp/oxygen setup with the 1lb bottles has poor pressure regulation. not too big of a deal when working with .09 wall 4130 tubes. but when you get into thin wall, heat treated tubing like 853 you can easily ruin a tubeset. Secondly those 1lb oxygen bottles don't last more than a few minutes, last I looked they were about $8 each.
I still use a Benzonmatic (mapp) for lugged construction but only to piss off people who claim it can't be done right. I built two fillet brazed frames a few years ago using a Benzonmatic but it wasn't easy. I also have the benefit of 25 years experience brazing. You will have a shorter learning curve and better results if you use a proper Oxy/acetylene ( or Oxy/propane) setup.
Small Oxy/acetylene setups with tanks can be found for under $300 new and I have seen used ones with tanks for under $100. some tool rental places will rent them to you.
10-19-08, 07:47 PM
Interesting. It will be Thanksgiving break before I can really start practicing and then Christmas hopefully I will have a frame to show for all the questions I have asked over the years. Thanks for the info everybody.
"not proper brazed joint?"
I don't mean it will fall apart. And I am speaking here of plain MAPP, no O2. I noticed that the colder processes would require a much longer run up time, parts will get really hot, and sometimes flux will go off, with the risk of impurities. It's like welding, the harder you hit it the better it will go, even though/because in either case too much heat would be bad. So when doing joints some of them maybe because of how they dealt with the heat, I would touch with silver, and the silver would go in there without effort. But in other cases it would be more of a struggle, getting the joint to sufficient heat all at once. I went to MAPP, and I went back to propane. I have OP, and TIG, etc... But I am still interested in what could work etc... MAPP was hotter and seemed easier to work with. Propane seemed to keep the flux cleaner.
The reality is that any number of knives have been forged, and some even forge welded with nothing more than a single burner propane torch. One could certainly do bandsaw blades with silver. I was just reading an old article about Mercian, where they didn't like OA because it could be too hot and dangerous. Well that obviously isn't true either, but Mercian had a way of doing it in propane.
I looked it up and OM is very nearly as hot as OA, so the results should be similar. OP is about 1000F cooler, and while OM is only about 300 degrees cooler.
10-21-08, 03:10 PM
I used a bernzomatic mapp/O2 torch to install 2 downtube cable stops, fill in 2 dents, and add a pair of waterbottle bosses.
It works fine. O2 bottles are very expensive since they only last 5-7 minutes. Mapp lasts 20-25 minutes, or 3-4 O2 bottles worth. Temperature-wise this gets you close to an OA rig - at much higher cost per minute of work.
Bernzomatic also sells a torch that uses mapp and atmospheric O2 - it's obviously less expensive, burns cooler without the rich oxidizer source, but will still melt brass/bronze brazing rod - so it will work as well, but not as hot/fast.
Bernzo rig probably would work even better if you're using silver braze. I wasn't due to cost, plus added convenience of berno brass/bronze/nickel brazing rods 2 feet from the torch display at Home Depot.
The Bernzo rigs are ok for small jobs, where you can't justify added cost of an OA rig. I would not want to undertake a big job with one due to the time requirement of the process. I'd find an OA rig if I were to attempt an entire frame, which I probably won't - I can almost always find a used frame cheaper than diy.
"but will still melt brass/bronze brazing rod - so it will work as well, but not as hot/fast."
What the heat has to do is heat the object being brazed hot enough that a rod brought in contact with the object either melts to form a fillet, or wicks in with lugs. Heat sufficient to melt the brass rod is not the key. Though it could be the level required in a particular case. Once one has the hang of it one can help the rod to melt with the torch, but only if the object is hot enough. In the case of thin walls, and thickish rods there may not be the heat required in the metal to melt the rod, so it has to be balanced. The heat required to braze a BB is greater than that to braze a rack tube.
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