Dan Bailey is a Minneapolis frame builder whose shop is called Pallas Athena Custom Bicycles and he’s been walking us through the construction of custom a cyclocross frame. Here’s Step 2.
Tacked and tinned: Once everything is prepped and ready, the seat tube and bottom bracket shell go into the fixture and are tacked and “tinned”… an internal fillet is formed by using heat and capillary action to pull molten bronze to the inside of the joint. Once that’s done, and the flux has been soaked off, the next step is to mock everything up in the fixture. At this time, I figure out where the down tube intersects the BB shell, and mark it off.
Vent hole: The seat tube/BB combo comes out of the fixture long enough to drill a vent hole. In this case, a 1/2″ will do nicely. I could have gone slightly larger, but chose to be a little conservative. Once that was done, everything went back into the fixture for a final fit-up.
Flux: If everything looks good at this point, it all gets coated with flux (inside and out), and then the rest of the front triangle is tacked and tinned. Of course, I didn’t manage to get pictures after this was done because I was pretty exhausted and needed a beer and some Battlefield 3 time before I called it an evening.
Raw Fillet: At all the joints, you then build your fillets—ideally neat little piles of brass encircling the joint. The cleaner these are, the easier they are to finish. The one shown above isn’t too bad. The bike then goes into the soak tank to remove all the flux (which turns into a water-soluble glass during the brazing process).
Then the real fun begins—cleaning these fillets. It’s a tedious process, and is interrupted by the need to go in from time to time and fill in pinholes or low spots with a bit of silver. The worse you are at laying down the bronze, the more money you’re going to have to spend on silver, filling in your mistakes. The tools here are generally a round file, strips of sandpaper, and if you’re brave — a dynafile, which can do horrible things to your frame if you don’t do a good job of controlling it. In the end, your fillet should look something like this:
Alignment: Once you’ve done this to all the fillets on the front triangle, the next step is to check the alignment of the front triangle and cold-set as necessary. In this case, we were dead-on straight—second frame in a row that’s happened—and didn’t need to make any major adjustments.
Back in the fixture: With that, we go back into the fixture for the next step: the rear triangle.
Dan Bailey is the owner of Pallas Athena Custom Bicycles and is still very much a rookie builder. When not obsessing over bikes, he makes his living in marketing, and spends whatever free time he can with his wife and son.
Previously: Athena Bikes: Build Process Step 1