Seat Tube Angles, Head Tube Angles, and The Down Tube in Between

If your going to go custom, then go custom. My calculations call for a 73.3 degree seat tube angle, so we shall have one.

Bolted down and secure

Now time to mark the tube with the correct butt placement. The down tube will have a thick butt of around 100mm at the head tube, and around 40 at the bottom bracket. I good practice to place the longer thicker end at the head tube, there is more bending force there than the bottom bracket.

I started with the headtube miter first.

The target was 58.8 degrees. I say 5/100ths of a degree off is a good tolerance. when built this should result in a 71.5 degree seat tube angle.

Mitered and cradling the head tube this one is done.

The other end is a little more complicated since you have to miter both the bottom bracket and the seat tube. With hand tools that oval shape is a process file, try, file more, try again, repeat.

 Getting real close here.

Now time to braze and align. 73.3 seat tube angle, 71.5 head tube angle, 550 top tube, and 66mm bottom bracket drop.