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 Post subject: Re: welding vs brazing
PostPosted: February 8, 2012, 1:47 pm 
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Joined: February 8, 2012, 12:35 am
Posts: 53
Location: Langdon,AB
On the topic of welding vs brazing, brazing was used for various reasons, one of which was the lack of good welders with the relatively "new" arc welding processes at the time.
Another was the amount of heat, and resulting stress at the tube joints. Brazing, which by definition means no melting of any base/parent metals, offers a much better HAZ (heat affected zone) than arc welding when we talk about alloys like 4130. The brazing method also uses a larger weld profile. While this may seem like a detriment, it serves to reduce the notch effect inherent in some tube joints. In the event of a crash, brazed joints have great ductility. A bending rather than breaking type situation. It served to give a much smoother look to the joints, and the rate of heating placed more heat into the structure at a slower rate and over a larger area. Again, helping avoid ill effects on heat-treatable alloys like 4130.
Now, NASCAR uses MIG, and NHRA TIG, and nobody uses brazing in motorsports at a pro-level. Bike frames are still made this way on a very small scale. One other reason that it works good is the reduced warping of the slower, less extreme heat applied.
I prefer TIG welding myself as I'm certified with it on 4130 and many other metals. I think MIG can work, but is a compromise in ultimate quality. For the 1018 stuff, it's fine. I'm going to build my frame from 4130, so I'll use TIG.
One thing to think about when designing your chassis on another note, is the surface area of the weldement, and notch effect. This is why I strongly encourage round tubing. A proper cope for a round tubing joint has good surface area and the stress is spread over a larger area. The differences are small, but it all adds up when things go sideways..!

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 Post subject: Re: welding vs brazing
PostPosted: April 2, 2016, 11:49 am 
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Joined: August 18, 2015, 12:41 pm
Posts: 118
Location: Seattle area (Woodinville)
The Tim Paterek CD set on building lugless bicycle frames has a good tutorial on fillet brazing.
http://www.timpaterek.com/videos_dvd.htm

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 Post subject: Re: welding vs brazing
PostPosted: April 8, 2016, 1:54 pm 
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Joined: February 9, 2016, 8:46 am
Posts: 392
Location: New Jersey
Good thread. I felt the need to chime in.
1) I am a certified welder and certified welding inspector. As with so many things in life, there is more than one "Right" way to accomplish a given task. People will tend to stay in their comfort zone, and that is fine. Each of the processes discussed above have advantages and disadvantages. What I will say is that on a very tangible level, I have tested and certified many welders over the past ten years, and one thing I can say with absolute certainty is that if you are going to be welding these chassis, if you have not had your eyes checked in a few years, do so. Probably 75% of the welders that fail a welding cert. test, do so because they cannot frankly see what they are doing properly.
2) I know this is a "locost" forum, and that welding equipment is a major investment for a hobby. I strongly encourage people to buy a name brand piece of equipment from a local distributor. Support and parts are much easier to deal with, and many distributors will even help you set up the machine for the intended purpose. That is invaluable for those that have never welded before. While the internet is a great source of information, as we all know there is also a LOT of misinformation. With respect to GMAW, or Mig, I also recommend that you clean all pieces before welding, and make a few test pieces to cut apart to make sure you are getting good penetration. Since these projects will most likely all be in short circuit mode, it is very easy to have a good looking fillet weld, and have absolutely zero penetration on one side or the other of the joint if it is not clean

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