With proper technique you should be able to have crisp shorelines without the need for any filing right from the start. The three students that are presently in my framebuilding class were able to do this (have perfect shorelines) on their first frame they brazed together this last Thursday. It is also one of the hardest things about brazing to get the hang of at first.
Good shorelines begins with a close fit between the lug and the tube. If there are gaps caused by using a lug with a different angle, a loose fit, or carelessly wiggling the tubes into the lugs during assembly, it is necessary to close them up before brazing. If you don't do this then the silver will likely shrink away from the gap as it cools. It looks ugly and says to everyone that you are a beginner.
Second, you need someplace for the extra silver to go. On the head lugs it would be the head tube sticking beyond the lugs and on the seat lug it would be the extra seat tube length poking above the seat lug. I call this tubing sticking out beyond the lugs the "dumping ground" where excess silver can go and be cut off later. It isn't so much about melting the perfect amount of silver (so as not put the tiniest too much on) but rather knowing how to get it to this extra tubing to be cut off later.
Third, I ran my torch over the shoreline after an area has been filled to see if there are any gaps or extra silver. If I am doing a down tube lug, I fill the down tube part first and direct any extra out onto the head tube. After filling that part, I run my flame over the down tube shorelines to see that they are perfect. Any extra is directed in a channel I create to get it onto the head tube. Once I have filled all the area of the head tube, I again run my torch over the head tube shorelines directing any extra towards the front band. It is this part of the lug that accepts the extra silver and, if there is too much total, it will be easy to flow it from the top of the band to the bottom – where it will be cut off latter (the “dumping ground”). The Curt Goodrich technique is to flow any extra from the other lug areas onto this front band and what little extra needs to be added, do it from the area to be cut off so that the perfect amount is used without a drop of waste.
What students have a hard time doing at first is matching the speed of moving the torch with the speed at which the silver will melt and flow when cleaning shorelines. It is not just the speed they have have to keep track of but also the distance, direction (angle) and accuracy of the position of the flame. Everyone seems to have a tendency of going too slow at first and too fast at the end. Good brazing technique depends on reading the indicators at the joint and responding naturally to them without having to think of what you are doing.
Actually there is a lot more information then this brief outline provides on how to braze lugs. I have 8 pages of techniques in my framebuilding class manual and I talk about a lot more in class. And of course an instructor proving feedback while brazing is the best and fastest way to learn. Frankly I want my students to have a competitive knowledge advantage over other beginners and do good work right from the start. Poorly made stuff can hang around a long time to represent what you do.
Doug Fattic
Niles, Michigan