How Do I Design A Frame?
There are many considerations that go into designing a frame, far more than can be answered here. First, of course, is the rider: a custom frame will be designed around your particular leg length, torso length, arm length, and preferred riding position.
Then there is the intended use of the bike: do you want a fast-handling crit bike, or a loaded touring bike that handles smoothly descending the Alps with 50 lbs. of gear? What diameter of wheels and width of tires do you want to use? Do you need fender clearance? What size are your shoes? (Seriously: shoe size affects toe clip clearance in front and chainstay and pannier clearances in back. If you will be touring in mountain bike shoes or even boots, you may need more room than if you stick to sleek road riding shoes.)
For an amateur, a great introduction to the design and construction of a lugged steel bicycle frame is Lugged Bicycle Frame Construction, A Manual for the First Time Builder: Expanded Second Edition, by Marc-Andre Chimonas. This is an excellent introduction from an amateur builder who decided to share his experience in a self-published book. The book combines straightforward instruction with the author's personal opinions on frame issues. Take the opinions with a grain of salt, but the directions will step you through the process clearly.
Another excellent guide is now out of print, Richard Talbot's aptly named Designing and Building Your Own Frameset: An Illustrated Guide for the Amateur Bicycle Builder published by the Manet Guild. Talbot discusses both theory and practice of building a lugged steel road frame, including building your own jigs. The emphasis is on hand labor, not machine tools -- he assumes you will miter your tube joints by hand with files and scrapers, not stick the tubes in a milling machine. There's an introduction to brazing and materials, too, though it's specifically *not* a beginner's guide to brazing -- Talbot suggests looking for a local vocational school to learn how to braze, since practice is essential. The design considerations apply no matter what construction method you plan to use, so this is still a useful book for the welders out there.Here's a picture of a very simple frame jig made from plywood and angle iron, similar to what Talbot describes. I drew the frame design full-scale on a sheet of plywood, cut out gaps for brazing joints, and shimmed angle iron out from the surface to get the tubes into the same plane. This is what I built my first frame on, and it came out within a millimeter of perfectly aligned. Fancy production jigs make changing the jig setup quick and easy, but they really aren't needed for do-it-yourself scale production.
Henry James Bicycles, Inc. Henry James is a n excellent source for books, tools, supplies, and frame building parts. . His main business is making and selling beautiful cast lugs, fork crowns, and bottom brackets in both CrMo and stainless steel. He also stocks brazing supplies, his own beautiful, well-thought-out frame and fork jigs, and Tim Paterek's two-part video on fillet brazing. If you're seriously interested in building more than one bike, order Paterek's book from Henry James and ask for a price list, too.
Other Good References on Frame Design and Bike Fit
While Talbot and Paterek both tell you how to design a frame, there are many ways of sizing a frame to fit a particular person, and no one way can be taken as gospel. The following are good references for bike fit, though most do not directly address actually designing a frame.
This page written by Josh Putnam. Please feel free to email questions, comments, corrections, suggestions, etc.
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