Framebuilding with Dave Bohm: Days 1 and 2

There’s no need to bore you with details of my flight and shuttle bus ride to get to Dave’s workshop and my home for the next two weeks, so I’ll cut straight to the first day of class.

Dave greeted Cooper my classmate and me at 8:00 Monday morning. We spent nearly all day listening to Dave talk about the essential knowledge framebuilders should have before they start cutting steel and lighting a torch. We touched on the metallurgical properties of the different bicycle frame materials, from steel to titanium to aluminum. Dave discussed the concepts of tensile strength, yield, and elongation and how they play a roll in designing and using bicycle tubing. He also talked about how different tube wall thicknesses and tube diameters can affect ride quality.

Although I was familiar with some of the concepts, it was beneficial to jog my memory and to take that knowledge and apply it to the tubing choices Cooper and I were asked to make for our own bike frames.

But before we could get too far in our tube choices, Dave provided some information and his opinions about front end geometry and how it affects handling. Front end geometry, especially the measurement known as trail, is one of the most controversial topics among bike geeks today. You have guys like über randonneur and Bicycle Quarterly producer Jan Heine, who champions a low trail figure combined with large, supple 650b tires and then you have pretty much everyone else in the bike industry continuing to use mid or high trail figures.

It’s hard to ignore Jan’s voice, even though it goes against the ideas of most in the industry. In a way that’s why I believe many people are drawn to his ideas. Since most of us haven’t had an opportunity to ride a low trail bike, we’re drawn to the idea of riding something totally different and in theory something that is superior to what we’re used to.

I admit that I’m among the small but growing crowd of Bicycle Quarterly readers who is dying to try out one of Jan’s optimized designs. But unlike many, I’ve already owned a bike with low trail and it shimmied enough that I sold it. So why would I let myself be lured back to Jan’s paradise? I have no other reason except that I want to try it again. I’m hoping that by tweaking the design to suit my weight and riding style, I’ll be able to build a wonderful new bike frame.

Day 2

On Tuesday we got to get our hands dirty. Dave spent a bit of time in the morning talking about brazing science and safety and then we we took action.

We first practiced melting bronze rod onto some steel bar stock to get a feel for how to wield the torch and rod. After a bit of practice, we moved onto brazing a piece of steel tube to the steel bar stock. We focused on building up a pool of bronze while trying to maintain a consistent width around the joined pieces.

Although I have some frames under my belt, it was nice to go over the mechanics of creating a good looking and strong connection. Once we brazed a few tubes onto our bar stock, it was time to braze tube to tube. But first we had to learn to miter a tube so it would fit accurately with its soon-to-be partner for life. We broke out some hand files and went to town. I was comfortable doing this and my mitred tube turned out pretty well.

Joining tube to tube is much harder than tube to bar stock. While the concepts are the same, it can get tricky to start brazing when your joint isn’t following a flat surface. Overall I was happy with my performance, but it was obvious that I’m nowhere near where I’d need to be to call myself a professional. Dave on the other hand laid down a fillet like a boss. Add heat, add filler, remove filler, remove heat. Bam. Do it again. Bam. He did it so fluidly. This is why I spent money to come to Tucson. It’s so much easier to learn while watching someone do it in person then to try it yourself than it is to futz around in your own garage continuing to not learn from your experience.