how to build this part

Hello,
First, I'm not a mechanical engineer, just some other kind (EE), with a
one-time mechanical problem. I need to find a way to make a steel cone,
with a thin wall section, like in a funnel. The problem is that the size
at the small end is too small for any sheet metal roller I have ever
seen, else this would be easy.
The cone is destined to go on the tapered end of a crankshaft driving a
generator, which is direct coupled to the tapered shaft. I need to
adjust the spacing between the engine and generator housing so that the
far end of the generator's rotor shaft is in the right place. Currently
tightening the long bolt through the rotor pulls the outer support
bearing partly out of the end housing supporting it, and misaligns the
brushes/rotor. I considered machining the housing on the engine, but
numbers are not working out. It looks like there would be a "break
through" of some thin casting sections if I cut out .100" to move the
generator into correct "Z" depth.
So, anyone have a suggestion for how to make said thin funnel shape?
wall thickness needs to be .010", very tight tolerance, as the taper is
1-to-5 on the shafts.
TIA,
Bill
ps: hi-tech approaches are not economically feasible..