You can obtain D cutter material from some of the suppliers of cutter steel.
I've used the cobalt steel D material for some cutters of the larger sizes
that I used to work with when making plastic injection molds. This makes
the making of a single lip cutter easy.
Just turn the tip part to the diameter you want and taper if desired to the
shape you need. Then put the cutter on the cutter grinder or other grinding
tool that you may have available and grind the majority of the back of the D
down a thou or so and lead that smaller diameter right up to the cutting lip
with a straight section from the inner diameter to the point of the cutting
edge. If you're doing a rounded cutter, you want to do this all the way to
the bottom of the cutter. If you have a flat bottom cutter, you want to do
a few (two-three) degree angle on the cutter bottom so that the cutting lip
is the lowest point on the cutter and the rest of the bottom is a gentle
slope up from the bottom and there is relief behind the cutting tip.

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