Topic: Brazing

[1976Thunder]

Ok just bought a house and got engaged. So I am broke and top it off my wielder has gone to the big arc in the sky last week. I am starting a cafe 77 550K soon. Has any one used brazing for there builds how strong is it and where are the no,no's. Thanks Jeff

[Spikeybike]

i wouldn't , it may work, and it may hold , but tensile strength of brazing is far lower than actually welding
 
thats your life in your hands, do you really want to take that chance

[1976Thunder]

I was hoping just to use it for seat brackets tank things like that. Any frame work I think I will just farm out.

[Spikeybike]

I was hoping just to use it for seat brackets tank things like that. Any frame work I think I will just farm out.

i see , well as long as it's nothing structural it should hold,

[1976Thunder]

Do you think it would hold to the vibration and temp changes?

[Spikeybike]

it all depends on what its holding :

 3 brackets on side covers -no problem

 2 brackets on full gas tank- not so sure

and so on

i wouldn't worry about temp changes

[1976Thunder]

Thanks that's what I needed to know.

[Spikeybike]

anytime 

[Gregorymoto]

If you are talking about oxyacetylene welding, you can do what need to do. But you need to be good at it and know how to set up your joint.
How you set up the joint is everything in oxyacetylene welding.

I don't want to be completely contradictory but most early motorcycle frames where oxyacetylene welded, HD, BSA, and the good old Bultaco.
You just have to be good.

As far as welding tabs for your tank and stuff that will not kill you if it cracks and falls off, go for it. Just do a bunch of welds on some scrap that is the same thickness as the material you working with and bench test it using a vice and a hammer, vicegrips, or what ever you can find to stress the hell out of the weld.

I oxyacetylene welded on my kick stand 15 years ago and it is still there. You just need to practice.
Good Luck to you.

[Spikeybike]

oxyacetylene welding and brazing are different.   brazing is similar to soldering  (only way hotter)

[Gregorymoto]

Brazing is when you join two dissimilar metals together to the joint, and start adding new dissimilar metals.

If you take to peaces of steal and melt them together neatly that is welding.

I know.

[Gregorymoto]

It sounds like he wants to weld not braze.

[Gregorymoto]

I should have put out the definition first.

[kghost]

None of ya can spell "weild" or steal" ....

I'm not letting ya near my bikes.

[Gregorymoto]

Ya i know my written skill is in math not English, and I'm half white trash knuckle drager. So cut me some slack

[kghost]

BTW brazing is the joining of two parts by use of a non ferrous filler.

The filler works by capillary action when heated and interacts with the base metal. Example: silver brazing.

Brazed joints are usually about 1/3 the strength of traditional joints.

Braze welding on the other hand involves brass or bronze. It does not use capillary action.

Brass has a strength close to mild steel.



Oxyacetylene is welding. One type anyways.

Still the perferred type in aircraft structures as it anneals the joint as it welds.


Wether its brazing or welding really depends on who you talk to but specifically the temperature at which the joining occurs.

[Gregorymoto]

ya i know i read the book more than once,
 You can braze with oxyac.

 I'm guessing the guy was talking about using MAP gas or something, i just automatically assumed he was using oxyacetylene brazing, why not weld it i thought.

Guess i should have thought it over a bit.

[kghost]

Well it sure was ambiguous.

I'm thinking he was gonna use butane or something (propane etc).

I guess if he had an oxy fuel set up...I'd scratch my head as you did....wondering why he just didn't weld it

I've seen good results with silver solder and some of it can be tough as nails....

Some of the old bikes were brazed together with brass/bronze.

I sure wouldn't wanna ride down the freeway on something brazed together tho.

Thats just me...

[Gregorymoto]

Ow man have you ever been on a bultaco. I had one and knocked and kick the hell out of it on trails and small jumps and it had the hell kicked out of it before i bought it. That dirt bike was a dream as far as handling and frame strength, never a crack or bend.

Take care

[kghost]

Right on. 

Happy Saint Patties

[Jinxracing]

Simple definitions as far as I've been taught...

Brazing: Joining two or more pieces of material together with a filler material that does NOT fuse with the base metal.
Welding: Joining two or more pieces of material together with a filler material that DOES fuse with the base metal.

That's why people compare brazing to soldering...it doesn't actually melt the base metal like welding does.

As far as the strength of a brazed joint vs. a welded joint, I've been told over and over again by my bicycle and motorcycle frame-building uncle that a properly designed and executed brazed joint is as strong, if not stronger than, a welded joint. "Why are modern frames welded instead of brazed then?" you may ask. From what I've observed watching the old fella brazing tubing together, brazing takes more of a "touch" than welding does and would be much more difficult to automate with robotic equipment. Plus, brazing is just plain hard to do.  On the upside, supposedly brazing will not screw with the heat-treat on CroMo tubing since it's done at a lower temperature than welding.

To quote the Wikipedia page on Brazing: "Brazing is different from welding, where higher temperatures are used, the base material melts, and the filler material (if used at all) has the same composition as the base material. Given two joints with the same geometry, brazed joints are generally not as strong as welded joints although a properly designed and executed brazed joint can be stronger than the parent metal." There's that "skill" thing again. 

I'd love to have brazed joints on the parts I build, but that's a set of skills I sure don't have.  I let my buddy and his MIG welder fuse metal for me and it seems to work just fine.

[oldbiker]

Dave Kerby, a very respected frame builder in the UK built all his frames with Brazed joints with never a failure.
He taught me so I could build my own frames.
It is importamt that the joint is Physically close before making the join
and care must be taken not to overheat. (just sufficient to run the brass or bronze into the whole joint)
In one respect brazing is better than welding as it introduces less stress into the parent metal due to localised overheating.
Also despite what someone said, when I was working at the Triumph Motorcycle factory in the late 50's and early 60's all the frames were assembled with tubes brazed into the cast iron lugs.

[Steve F]

I think the key to proper brazing vs. welding is a perfect mating of the parts prior to the brazing process.  Any gaps in the joint leads to a weak joint with excess amounts of the braze filler to stand up to the stress.  I've known a fellow for a number of years that had scratch-built aircraft frames and a few other aircraft parts from chrome moly tubing and he recommended oxy acetylene WELDING over electric welding to prevent the chrome moly from cracking.  I also heard that the frame cannot be certified by the FAA if it was electric welded and not anealed afterwards in a furnace (?) just hear-say there, but it makes sense.

[crazypj]

I believe almost all Reynolds 531 frames were sif-bronze braze welded as the technology to actually weld them wasn't very good when material was developed and actual welding destroyed the properties of the Chrome-moly tube. Don't remember Rickman, et al having too many problems with frames cracking, even with Triumph motors being 'scrambled'?
PJ

[kghost]

I think the key to proper brazing vs. welding is a perfect mating of the parts prior to the brazing process.  Any gaps in the joint leads to a weak joint with excess amounts of the braze filler to stand up to the stress.  I've known a fellow for a number of years that had scratch-built aircraft frames and a few other aircraft parts from chrome moly tubing and he recommended oxy acetylene WELDING over electric welding to prevent the chrome moly from cracking.  I also heard that the frame cannot be certified by the FAA if it was electric welded and not anealed afterwards in a furnace (?) just hear-say there, but it makes sense.

Yeah you have to go over the clusters with a rosebud tip. Annealing them. Least for aircraft.

Depending on the type of brazing...some intermingling with the base metal is acheived.

Once again it all boils down to temperature. If you melt the base metal its braze welding.

As for the strength of the braze...it depends on the base metal. Some will in fact be stronger than the base...provided that the base is relatively weak to start with.

Mild steel when brazed with bronze for example.

Purpose of the lugs on some frames was to first align then transmit stress thru the tube after it was brazed.

Anyone know if the lugs on the early frames were brazed as well?

[754]

Indian & Harley frames were furnaced brazed for a long time,
but,
I think they did have the odd plug weld.

I dont think brazing a frame has any strength issues if they are slip fit joints, then brazed.

On vintage bicycle frames they are often brazed which leaves a nice clean joint, and they hold up very well.. I probably could show a dozen examples tha are 50 years old if you come to visit..

Oh and St Pattie is a burger.. not the Irish dude..kghost..

[bryanj]

Hate to dissapont but ALL the old Brits were Brazed BUT most tube joints were "socketed" (tube inside a hole) not but jointed

[Gregorymoto]

My last comment.
Well thank god all the old bike builders figured it out and did it right and thank god for modern day welding technology and Miller Electrics.

[kghost]

Amen

[mark]

Until this evening, I hadn't brazed anything in ages....

Sandblasted the heck out of my header and found one little pinhole a few inches ahead of the collector. The mig would probably just make the hole bigger. GAG!!! No O2 in the tank, either. Found that a propane plumber's torch would get the area bright red - enough to melt a puddle of silver brazing wire on there. As long as the pipe doesn't get red-hot that far down, it should stay there ok. I hope.


As for seat and tank mounts, I'd weld them. Tank repairs? That's something else entirely.

....thank god for modern day welding technology and Miller Electrics.

The Lincoln aint bad either.


Happy trails.

[1976Thunder]

Thanks guys and yes I was talking about oxyacetylene. I have a real nice set up that I use for building bicycles. I have ordered some high tensile rod. This is going to be the first bike I build and not just motor and one thing I have learned from years of doing it wrong is ask someone that knows first.