From years of experience grinding tools and job shop machinist.
The basics are to dress a radius on a grinding wheel, then spin the tool and press it to the grinding wheel.
A simple radius is the easiest way...you can even make your own tool to swing a single point diamond dresser to create the radius.
A toolpost grinder might work....a surface grinder is what we used in shops where we had one, a tool and cutter grinder when I worked in a tool and cutter grind shop. I'd probably rough turn, flute, heat treat, then spin the form on.
Once you have your form you can black it up with a sharpie and back it off to a hair land, most shops I have worked in had one of these...
https://portal-images.azureedge.net/...pg?w=540&h=360
The tool could be held in a vee block and the angle set (7 degree primary usually) and you work at it carefully by hand until just a hair of the original form remains. Thinking out loud here I bet a small belt sander could be carefully used the same way.
For ease of getting the form clear around to the pilot, I might make the pilot fit into a hole through the center, so you can remove it to create and sharpen the tool, then slide it in later.
Any helix greatly complicates things...straight flute will be easiest.
There was a grinder type made that was perfect for all of this stuff.
http://img0112.popscreencdn.com/1622...grinder-w-.jpg
They are floating around out there in the world in a variety of types and sizes, the "deckel" was a tool used to make molds I think...the grinder shown is made to create a D type cutter, single lip, but many had indexing to address multiple flutes