By James A Morikawa
In 1998 I began searching for a method of tube mitering to replace my unsatifactory hole-saw methods. I came upon the idea of using abrasive sander belts. I first heard mention on this from a very cool dude Dave Bohm (Bohemian Bicycles). I believe Dave went on to designing this own, and currently uses it. Well, in 1998 there was no such belt-miter availiable for a framebuilder, none that I knew of. It was just an idea. So, I designed, fabricated, and tested a bunch of my own.
After about 5 years of "trail and error" that idea evolved to what I have, and use today; the belt-miter pictured below. Along with it's use, evolved a personal method of mitering, and building a frame.
I now miter the majority of my tubes using my abrasive belt miter. I can miter faster, and more economically using it. There are still occasions where only the lathe or mill (with holesaws) will work, but this is rare.
Above is a typical example of a top-tube readied for mitering. There is no "feed-screw", or "crank handles". The tube is feed into the moving belt by hand pressure. The tube holding fixture slides laterally between the two guide-rails of the baseplate. The sliding surfaces are waxed for slide-lubrication, and wear prevention.
Seat-stays setup for mitering. Presently this fixture works only on seat-stays. Chain-stays are done one at a time, and I do chainstays quickly. There are various diameter rollers to accomodate the desired miter sizes. Roller diameter can also be simmed up with 2 inch wide masking tape. I can change a roller in about 1 to 2 minutes.
Here's some examples of the mitered joints I can consistanly obtain.
Wishing you an excellent day.