-"Des Bromilow" wrote
-The drill rod (silver steel in my neck of the woods) will be machined
-up, and then hardened and tempered as best I can in a home workshop.

-I'll see if I can scare up some cast iron for the bull wheel, or
-default to mild steel if I can't obtain it.
-thanks,
-Des

You could make one (or 2?) from aluminum and then risk the cutter on a
free-machining steel. I bought some "1018 CRS Shafting" from a bearing
dealer that machines quite easily, nearly like 12L14.
This stuff, without the key slot:
http://www.keystonemfg.com/trukeyoverview.php/

In my experience the "water anneal" makes flame-cut hot rolled steel
machine well. Heat red, cool until color disappears, quench. I don't
bother to do it unless the metal had hard spots and the first cut left
a rough finish.

Scrap hydraulic cylinder rod also machines well, after removing the
outer case. I got some short rod stock cut-offs from a local cylinder
manufacturer's scrap bin. Compare Nitralloy's machinability to low and
medium carbon steels:
http://www.a-i-t.com/machinability-rating-chart

Here's a similar method with a single-point rack shaped cutter ground
from a lathe bit, which cuts slower than a hob but was quick to make
accurately on my surface grinder and can spin at HSS instead of carbon
steel speed.
https://picasaweb.google.com/KB1DAL/...10370886636434
The teeth are ragged because the cutting force overpowers the index's
weak small-diameter spindle lock.

I roughed out the blank with a faster-cutting standard gear cutter:
https://picasaweb.google.com/KB1DAL/...10360947850418

jsw