How I build a frame
I started this blog with the intent to show my readers how I fabricate frames and forks. The blog has morphed a bit to become a place to update customers on progress. I will keep the progress reports coming, but I want to get back to my original plan. I have taken a lot of photos of the build process of Nathan’s bike, and I will lay them out in installments. This first installment shows the first steps of machining the tubes and prepping some of the castings.
First step is to give the new frame an identity. And not just some cold number, but a name to go with it.
Here are the materials all laid out. Tubing from left are seat stays, chain stays, down tube, seat tube, top tube, head tube. Note the markings on the main tubes. Those indicate the butt transitions where the tubes go from thick on the ends to thin in the middle. The rear dropouts and seat stay bridge are shown on the left. The lugs and BB are on the right.
The next cut makes room for where the down tube and seat tube overlap. This cut is at 90 degrees to the first cut and approximately 60 degrees to the down tube. The rotory table sets the ST/DT angle and the upright peg sets the tube perpendicular to the first cut.
This precision turned dowel is set on the fixture and the tube is butted against it. This dowel is parallel to the cutter. This keeps the miters in perfect plane with each other and helps create a straight frame.
Next is the down tube. There are 3 cuts on the down tube. One where the tube butts against the head tube, one to give it the shape of the inside of the BB shell, and a third where the seat tube and down tube overlap. What’s that you say? Didn’t we take care of that with the second cut on the seat tube? Yes, but I hate looking into the shell and seeing a piece of tubing just hanging there not doing anything. So I cut it off. And then when you look into the BB shell, all you see is a nice, clean interior.
The down tube cut length is set and the peg sets the tube perpendicular to the first cut.
And then the third cut is made.