Hi Mike,
Welcome back to the trade. You might want to ask this question and similar ones across the hall on the framebuilders list. BikeCAD is an excellent program. It will convert a tube's center to center measurement into miter edge distances. Of course its primary purpose is to replace the need to do a full scale drawing necessary to create the geometry of a frame on a drafting board. In addition, it can help you convert body measurements into frame dimensions. The formulas to do this are customizable.
I don't use either a full scale drawing or BikeCAD to design my frames. I use a design fixture somewhat common in England (but not in the States) that I think F.W. Evans either invented or at least took credit for being superior back in the 30's or 40's. I place the actual seat, seatpost and stem I'm going to use on my fixture in the position that bests suits the rider. This placement is discovered with the use of a fitting bicycle and verified by replicating it on an actual bicycle. I slide the pieces on the jig that represent the tubes into the geometry that bests holds those components for its intended use. The tube holders on the fixture make it easy to check the accuracy of miters. It can also hold the front triangle while it is spot brazed together.
I'm pretty happy because today I went to pick up 3 sets of fixtures I had laser cut out of stainless steel. I'll use them in my framebuilding classes (and sell them too). I've added a lot of bells and whistles over the years to the original concept.
If you want, I can email you the Excel spreadsheet I created that converts center to center tube lengths into miter edge lengths. You need to enter 6 dimensions. The desired tube length, head tube angle, seat tube angle, head tube diameter, top tube diameter and seat tube diameter. It will spit out both the top edge measurement and bottom edge measurement (which will be different if the angles are not parallel).
Doug Fattic Niles, Michigan USA (but got the concept for my fixture while living in the small village of Esholt, near the town of Shipley near the city of Bradford, West Yorkshire, England)
From: Michael Howard <95rivieramike@gmail.com>
I am looking to get back into the frame business and just checked out the bikecad program. Has anybody used this program and does it work well? I specifically want to know if it gives measurements, from miter edge to miter edge on top and down tubes. I'm sure it gives head tube lengths. I remember seeing an articles in Velo News about a year ago about a similar program that worked in Excel does anybody know where to find that program or any similar ones?
Mike Howard
Santa Fe Springs CA