Weld vs braze

[GearsforBrains]

I own a hand made Italian bicycle, all brazed. Why would they braze rather than weld?

Hi there Pro. Just so you know where i am coming from, I co worker of mine owns and operates his own small BMX freestyle bicycle company by the name of Bickhouse Bikes seen here. http://www.brickhousebikes.com/

I visited his shop down in Watsonville CA and where he shares floor space with a rode and cyclocross bike builder by the name of Rick. Rick owns Hunter bikes that you can check out here http://www.huntercycles.com/mainpage.html

While checking out the shop i noticed some of Ricks frames in his Jig. They too like your bike had brazed frames. When i asked my friend why Rick chooses to braze his frames, without lugs, and if they were weaker than the TIG welded frames i was used to seeing he let me in on a little debate going on in the bike world.

It turns out some frame builders prefer to braze because they believe that since the brazed joint has a larger profile than a small TIG welded joint, the load on the joint is spread out over a larger area and is thus stronger. Do i know if thats true? Nope. I am just passing on what was told to me. If you are familiar with cyclocross then you know its pretty tough on equipment. The very well made and brazed frames i have seen from Hunter are plenty strong.

[lwill]

I have had the luck to work with and learn from a very skilled weld that has welded on everything from aluminum foil to parts for the "Tokomak"(sp?) reactor at Livermore Labs and tryed to soak in as much info as possible.
I just saw this tread and hope you don't mind me throwing out a bunch of tid bits, and feel free to correct me if I get it wrong. I agree with alot that has already been said, but here is my 2-bits.

I too learned with a stick welder, and if you are good and have the right rods, they have a lot of advantages. They make rods to arc weld different types of steel under different conditions and even some types of Al. They can weld crappy, dirty metal (even galvanized, USE A RESPARATOR!) and have huge capacities for things like structural steel in buldings where conditions are not ideal. Also good for general repair like on farm / earth moving equipment. With a little practice sheet metal (22 ga+) is do-able, but be ready to fill holes. A good point is the rod is the only consumable. No gas, or tips to wear out. Down side is generaly ugly welds and spatter.

The first time I got my hands on a MIG, I fell in love! I also have a small Lincoln and have used it on steel (good), stainless (fair), and some AL (did the job), both with gas and flux core. It has its uses, but is not cut out for anything too big. Not enough power and to low a duty cycle (over heats). Still a great protable 110v machine. MIG is VERY easy, point and shoot. I think a trained monkey could MIG if his fur didn't catch on fire! If you have the money and power to run it, definately go for a bigger machine, once you get the hang of welding at higher settings, the control and quality of weld will blow away the smaller toy machines. We also have Miller 250's at our shop, very good welder for the money. Spatter is controlable with proper settings and practice. There are a few more consumables, and use the right gas for the type of metal. I beleave the 1/8" rating is for single pass. It is possible to use on thicker metal in multiple passes, but strength may suffer.

When I finaly moved up to TIG, I was in love all over again (sorry MIG) With the proper electrode and gas you can weld almost anything! (it is even possible to use it to braze with and heat objects)
My welder freind has told me stories of even welding dissimilar metals together (copper and stainless) TIG is like gas oxy/aceteline welding, torch in one hand creating a puddle, and filler rod in the other. It is very much like an electric torch more than a welder. There are diffent types of TIG, you need AC for AL and DC for steel, also different gas / gas mixes, and different tungstun electrodes. The thing with TIG, especialy AL is CLEAN metal, there is no flux or spattering to clean the gunk out of the bead and it will ruin a weld, gotta grind ALL the slag from a plasma cut. The killer for TIG is cost, our last Miller Sycrowave was will in the $1000's, but is ROCKS! TIG takes a LOT of practice, alot of my welds still look like crap because I rush to much but they still beat everything else hands down. Take your time and a good looking weld makes you feel like a real stud.

On braizing, it has it's uses. It can be used to join dissimalar metals. It will not eat into the base metal and weaken it.(heat stress is a different matter) It is in fact the best way to repair cast iron, because melting the base cast iron ruins it's crystal structure. A lot of bike frames are made like copper pipe fittings with the tubes slipping into a flange on the hub, etc. and are very thin wall. With this type of engagement, the metal parts are taking the all the strain and braizing acts more like a glue to keep them together giving a stronger joint than a butt weld ever would on that thin of a material. Braizing rod has a tensile streangth compairable to some steels and is less brittle. Also some exotic alloy's used in frames don't weld well.

If you can braize, or gas weld you can definatly MIG, and probably TIG with some practice.

Sorry, if I rambled on, but I have learned alot from Phil's posts and his site and wanted to share the the few nuggets I have. Thanks Phil.

Last point my welder friend taught me - "Prep is everything. A good welder grinds before he welds, not after."