Large brazing tip - good idea?

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An older book on welding & brazing that I found in our local library (from early 1980s) recommends using a larger tip and a "softer" flame - a little less oxygen too - when brazing.  The author said that the idea is to have a softer flame that will "brush" the surface of the metal to heat it, and obviously not to melt the steel but still it hot enough that the bronze rod will melt.But he said he thought it was good to use the larger tip, which can have this "brush" effect when the gas pressures are run lower.  The idea is to spread the heat, but not overconcentrate it.Is this good advice in your experience?  Or does it tend to offer no advantage while tending to over-use the gases?  Thanks.
Reply:A number 5 is a good tip for welding or brazing without using too much gas. It will heat quicker.Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:A. C. Davies, who had a whole stack of college degrees advocates something quite different in his book on welding. For cast iron brazing he says to use a tip about two sizes smaller than used for welding the same thickness of steel and to use a slight excess of oxygen. For galvanized steel he says use the smallest possible size tip for the thickness of metal and a slightly oxidizing flame. For brass and bronze welding (since the rod and base metal melt at the same temperature it can be called fusion welding) a larger size tip than that for steel welding is required because of conductivity. The flame should be oxidizing  and the best flame is found by trial which I won't go into. This is directly from his book. There are some magnified picture of the brass welds made a neutral flame, insufficient excess of oxygen and an adequate excess of oxygen. The effect on porosity is pretty dramatic.His book covers about ever welding process and I've used it ever since I've been welding. Any time I ran into something that gave me trouble I would grab his book and see what his process was. I have never found any wrong information in it.Last edited by Oldtimer; 11-04-2008 at 08:19 PM.
Reply:Depends on the job and if it needs or can stand high heat.Do you have an example in mind?A heavy casting that needs a lot of heat input requires a dirty big flame; but the roaring turbulent flame is not friendly to puddle control. Sometimes on a job like that two torches are used, one for general heating and one for working the filler.On sheet metal you may not want the added heat of a slow warming soft flame either; may be better to heat fast and local, braze a little, then get out and quench with a wet rag.If you're trying to get capillary or wick type of flow, then a soft enveloping flame gently warming the entire joint is probably best.Today I had to braze the handle on a brand new ball valve. Some "Italian Job" -  the threads on the stem did not match the nut. Concern #1 on that job was to make a connection before heat got to the  valve's packing. Yah, I took the pictures Last edited by denrep; 11-04-2008 at 09:09 PM.
Reply:Thanks, Oldtimer.  I will definitely try to find Davies' book.  Sounds like a great resource.Thanks, denrep.  You wrote: "If you're trying to get capillary or wick type of flow, then a soft enveloping flame gently warming the entire joint is probably best."  Yes, this was the kind of brazing I had in mind when I wrote the question - rather than "braze welding".  I've done some of both, but I was thinking of the kind of brazing that is actually very similar to soldering copper plumbing joints with 50/50.
Reply:According to my old manual, "A slightly reducing(excessive acetylene) flame is required and care must be taken to prevent the core of the flame from coming in contact with the metal" in the brazing section.Welding Technology, 2nd edition: Giachino/Weeks/Johnson; American Technical Publishers, Homewood IL, 1973.1973?  I bought it new in 93.  maybe the school book store had bought 20 thousand copies or something.  Still a good book though.Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:Originally Posted by denrepIf you're trying to get capillary or wick type of flow, then a soft enveloping flame gently warming the entire joint is probably best.
Reply:Originally Posted by Joel_BCWell, I also wonder if a large welding tip (say, a Victor #4 or #5 which I already own) is the best for this...
Reply:Originally Posted by denrepUnless you plan on running production, the tip you have is probably good enough, as long as nearby parts can survive the flame.
Reply:oldtimer this comes as a blow-- i  remember maybe wrong that gas welding waanted an oxygen-slightly deficient flame, so not to oxidize the steel but actually keep ox away, let the acetylene use it all up...