Mike, there are multiple good ways to build a frame as well as poor ones. What method is used is probably based on the particulars of specific equipment and how someone was taught. Most likely a pro learned from a master that had already weeded out bad techniques. Like most professional builders I know (I had the great fortune of learning from a master in Yorkshire) I don’t braze a main joint in a fixture for several reasons. It restricts optimum brazing positions and doesn’t allow the frame to move freely when it expands with heat.
The goal for lug brazing is to get compete silver coverage and have all the tubes end up in the same plane. Since they can move a lot while brazing it can be challenging to finish with an aligned frame. My procedure is to braze the seat tube to the BB 1st. This serves as my alignment foundation for the rest of the frame. Then I assemble all the main tubes into one of my main triangle fixtures I have laser cut and etched in Ukraine ($1000) that lays on my alignment table. I put 2 spots on the centerline of each lug (one on each tube). After it cools I align the frame on the flat table and put 2 more spots on that down tube lug on the available centerline places still left and align again. Now I braze that joint free outside of the fixture. Because the rest of the lugs allow for a little movement I can easily realign the frame again and put 2 more spots on the next lug (making a total of 4 on one lug before brazing). I align again before fully brazing that 2nd top tube lug. This align, spot, align and braze sequence insures I end up with a frame well within a tight tolerance. I don’t pin because with my method I need the joint to have a little ability to move to compensate for brazing distortion. All of my frame building class students that have not yet developed exceptional brazing skills to reduce distortion have ended up with frames well under 1mm out of alignment with this method.
Many builders successfully pin but that requires a very accurate fixture and/or set up on an alignment table. The origins of pinning comes from the European technique of hearth brazing when the whole joint or joints got entirely up to temperature before adding the brass so of course any spots would not be able to hold the frame’s position. That is how I brazed my 1st frame at Ellis Briggs in Shipley in 1975.
My method avoids the issue of the hockey stick possibly changing angles just a little. The old method British builders usually had some kind of make shift fixture to hold the down and head tube angle when they were brazing the hockey stick to avoid that problem. The equipment I got from Johnny Berry’s shop in Manchester after he passed away had a fixture to do just that. At Raleigh’s custom shop in Ilkeston I have a picture of them brazing a 753 hockey stick with angle iron holding the tubes while the whole 3 piece assembly lays on a steel table.
One of the greatest challenges of building a frame is getting a rear wheel to exactly center. That is why I don’t braze the chain stays with the down or seat tube. Too much is happening all at once to guarantee success. I also want to be able to file the lugs 1st without the rear getting in the way. It is a bit problematic to give too much detailed instructions in a subject post on the web. For example my frame building class manual which outlines framebuilding steps is 150 pages long. And even then I provide a lot more personal instruction so everything is clear.
Doug Fattic
Niles, Michigan