Old School Chopper Frame Fabrication - Knucklebuster

Figure 23
The slope angle of the 'ramp' should be forty degrees above horizontal (fifty degrees off vertical) and the length of the tangent
piece of straight tube should be four inches.
If you're 'off' by thirty minutes, (one half of a degree), or more, put those tubes in the scrap bin and try starting over again. In
all seriousness though you can be off by as much as one degree either way but if the bend is to tight you'll need to move the
lower rails forward slightly so the downtubes don't hit the motor's front cylinder head.
Part five
Once the forward bends are made in the lower rails its time to fit these into the upper section of the frame we've already
made. Specifically at this point we want to cut the tube miters where the uppermost portion of the down tube attaches to the
backbone.
The frames I build are based upon the old original Harley-Davidson frame design where the down tubes attach to the frame
backbone and not to the steering neck tube as you'll see on a lot of modern choppers. Figure 1 illustrates a stock Harley neck
and even though this particular neck is a casting the same design principal applies to a tube type neck.