I have recently been considering getting some brazing equipment so that I could make repairs to frames that have minor failures, rather than sending out to a frame builder for this service. Having taken UBI’s lugged frame building class a few years back, I had a general idea of what I might need, but didn’t want to go any further until I re-familiarized myself with the topic of brazing.
I found Marc-Andre Chimonas’ book, Lugged Bicycle Frame Construction, on the evil empire (Amazon) website, with what appeared to be some favorable and thoughtful reviews by actual readers. When the book arrived, I immediately delved into it and have now read if not studied much of the book.
It is written with a dry, understated wit, with an emphasis on the science of frame building. There are numerous zingers in the text, hidden amongst the tables and formulas. Consequently, I thoroughly enjoyed reading it. The author is a physician (which he describes as his “day job”), a writer (of both technical manuals and fiction), and a frame builder.
After reading just the first few chapters, I began to seriously question the idea that anyone can take a frame building class that lasts only two weeks, and from which an actual frame is produced. Whether that frame is safe to ride may be another thing altogether. My own frame has several flaws that can probably be corrected, but more on that later.
The book is logically organized and takes the reader through introductory concepts such as nomenclature, frame geometry, measurement and sizing protocols and includes helpful tables for determining angles and lengths for different sized riders. He naturally recommends smaller wheels for smaller frames, and there is a good discussion of toe overlap and bottom bracket height. He states his opinions about frame geometry as if they were facts, and that may irritate some readers, but I found it refreshing. For instance, recommended BB height is 25 cm for pretty much all types of normal road riding. This is a lot lower than you will find in production bikes.
Another interesting concept that I found both helpful and puzzling was the idea of controlling the variables in frame building. He differentiates between “operator controlled” variables and “outcome” variables. Outcome variables are the result of the frame builders operator controlled variables. But, he describes outcome variables to include BB drop and toe overlap, which in my mind are operator controlled. At any rate, what is clear is that frame design is a highly complex undertaking, and one that is aided by software. He recommends using excel and offers a link to a useful frame design spreadsheet, which is available on the author’s website.
There is a quick trigonometry and metallurgy review (which the author calls optional), and then the theory turns into fabrication as the author goes through chapters on frame parts, tools, mitering, torches, brazing technique, and lug modification. Again, the author doesn’t hesitate to state his recommendations, even down to a specific brand or manufacturer of a particular tool. For me, someone who didn’t take shop class in high school, the specific advice is extremely helpful.
After digesting many of the chapters, I decided to drag out the frame I completed 2 years ago but never finished filing or painting.
I built this frame for myself, designed around a 650b wheel size. I wanted enough front-center distance to allow for fenders and decent sized tires. The book uses a formula to determine an ideal length. I plugged my numbers into his formula and found that I won’t have toe overlap with this frame, so that is a relief. I did have to use a longer than usual (for me) top tube length to get this much front center distance (combined of course with all the other measurements). That means I’ll use a short reach stem when I eventually build the bike up.
One of the things that troubles me about my frame is that it was built so hastily and with so little actual knowledge. Well, after reading the brazing chapter I think I have reason to be concerned. I remember having a lot of trouble sanding enough material off the top of my fork blades, and off the inside of the fork crown so that the legs could be inserted without a lot of force. After hours of filing, I still wasn’t happy, but ran out of time so just brazed the fork legs into the crown even though the fit was tight. This is definitely a no-n0 – there needs to be enough room for the silver to flow into the joint.
Here are some other details of the frame I built. Using this book as a resource, I will be able to correct the other two (known) mistakes on the frame. I may decide, however to build a new fork. And, I now know what kind of equipment to purchase and how to use it safely, so I am looking forward to being able to do my own small repairs.