Things have been busy! Getting bikes out and working on other ones as well as a couple of side projects.
I took some photos in the shop this morning and figured I would do a little process post for those who are curious. I used to do these a lot and I think they are fun.
I designed these rings to look cool, but their main purpose is to beef up one of the most stressed interfaces on the frame. There are options for pre-made head tubes that are externally butted, but they are costly, inefficient to make, weigh more and most importantly only come in certain sizes. These rings allow me to make a strong interface for the frame and fork in any size I want, to perfectly match the rider's dimensions.
Here are the rings to start. They are made out of 4130 steel, the same material as all of my steel frames. The internal diameter is machined with 0.015" of clearance, just enough for a slip fit over the head tube stock and the silver solder to form a strong bond.
The head tube is rough cut with a hacksaw, about 5mm longer than needed. The edge does not need to be perfect now, because it will be faced down after the ring is attached.
Next the parts are cleaned and ready for flux.
I use high-temp flux for silver brazing, which comes in a paste form as seen about. When metal is hot it becomes susceptible to contaminants that exist in the atmosphere. When the flux is heated, it melts and turns into a clear "glass" that protects the metal from contamination and helps the silver flow. In TIG welding we use an inert gas, argon, to perform the same job.
I heat the tube and ring evenly, feeding the silver in on the outside edge that will be faced off, and pulling the silver through the joint with the heat from my oxy-acetylene torch. you can see how the flux has turned clear. The shore line is the line of silver (lighter color) that has pulled through. The nice consistent line seen above means no clean up work, which is what I like to see!
The flux is soaked off with a little bit of warm water, then the headtube gets hit with some scotch-brite to make it nice and shiny!
After that I put the tube in the lathe to turn off the excess tube and to face the edge which will be used as a reference in my frame fixture.
A couple of vent holes, and this headtube is ready to be attached to a frame!
Hope you enjoyed looking through that. New blog post on Colton's 29+ is coming up soon.
Thanks for looking!