Let's see... it's been a long time and I always do it with CAD now. You
are esentially slicing through a cylinder at an angle. That is an
elipse if memory serves. It's a parabol if you slice through a cone.

Anyway, it will take someone with good geometry skills or a CAD system
to lay out the elipse. Then you want to plot points along the elipse on
a grid, mayb 6"x6" or 3"x3" so you can transfer it to a layout table.

If you could give me the radius and angle of rise, I might be able to
get a few minutes in front of the CAD system and bang out a layout for
you.