Welding

• http://www.keenjunk.com/_junkyard/jp0004_2.htm
  
  

• IHPVA welding info.

• Rick Horwitz's Welding page

• Frame Building

• Bronze Welding for Lugless Bicycle Frames

• Structural Failures - Are Welds and bends incompatible?

• From: Giles Puckett giles@research.canon.com.au
  Subject: Brazing flame
  Qn: Can someone describe what a good flame for brazing looks and sounds like?
  Ans: Confessions of a self taught frame builder.
  Assuming you're talking about oxy-acetylene here.
  The chemistry varies from oxidising (too much O2) through neutral to reducing (too much acetylene). For most brasses you want neutral to slightly reducing, but oxidising will give a bit higher temperature if the parts are thick.
  Note the small light-blue flame cone inside the main flame, it's usually about 1/8" - 1/4" long.
  Oxidising flame - light blue cone is small, the flame roars, and in extreme cases it goes out with a loud snap!
  Reducing flame - light blue bit is longer, and there is a darker cone around it. In extreme cases it goes orange (like when you start the torch up with no O2 at all).
  Neutral - with a reducing flame, turn up the O2 until the darker cone just clears and you have a light blue cone inside a clear dark blue flame.
  The flame should be pretty quiet.

Qn: What size tip is recommended for doing general frame work?
Ans: Sorry, can't remember the number, but it's a pretty small one. Oxy-acetylene flames are VERY hot, so you can easily overheat the tubes and weaken them.

A related tip: the brass will go to hotter parts of the joint - keep the flame slightly ahead of where you want the next bit of brass to go, and keep the job turned so the brass doesn't all flow down hill if you're doing fillet brazing (with no lugs)
I've also found it useful, when brazing two pieces of different weights, to turn the flame to heat the thick piece more, and even to shade the thin piece with the rod for a few seconds to stop it overheating while the thick piece warms up.
Practice makes perfect yes, but brass is quite forgiving - you always know when your joint is good and when it isn't.

• From: Matt Houle
  To many brazers don't understand the importance of vent holes. Let's say, for example, that you are brazing the top tube to the seat tube, and you have already brazed the top tube to the head tube. While heating everything up to get to brazing temp., you are also heating up the air inside the top tube. You need a vent hole (at least one) to allow the heated (and expanded) air to escape. If you don't, it will be difficult to complete brazing the two tubes together properly. This is because the air will keep trying to push its way through your brass or silver as the filler cools. This isn't a problem with Tig welding, because the joint cools to below the melting point quicker.
  Earlier, I said at least one vent hole. Be sure to use two vent holes (water bottle bosses only count as one) if you want any water that gets inside to be able to drain properly.
  

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Thursday, 29 January 2009