Starting material: 2" sq alum, about 8" long, symmetrically tapered to about a 1x1 sq, which my calc tells me is only about 3.6 deg (arctan 0.5/8).
Seems to me the easiest way to do this is to tilt the 4th axis on the fadal, and just face mill away. I can actually get the dimensions pretty well by just manually finagling the angle, until the cut is right.
I have to thread both ends of this leg anyway (1/4, 5/16), so I figgered I'd put a 5/16 set screw in one end, and attach a pc of 1" round, for a 5c collet.
I think I have the "handedness" of stuff such that it should tighten the material on the screw, god willing.
I'll mount the 4th axis and tailstock on a sub plate, and tilt the whole bidniss. I have ideas on how to do this, but if there are standard or particularly nifty ones, I'm all ears.
Altho I proly won't do this right away, eventually I'd like to make a 4th axis subplate with two hinged ends, such that you could make the letter "Z".
Then, with one hinge bolted down, and the other hinge end bolted to some riser block, any angle can be readily achieved.
But, if there is a quick'n'dirty way to do this in a vise, I'm all ears. The only way I can think of is to leave a lot of material on one end, for a good grip, and have 8" sticking out of the vise, and at the correct angle, with stops/risers within the vise to set the angle. But then subsequent ops won't be so easy on a trapezoid, holding-wise.