DoN,

thanks for the reply...
the cutter cuts one full tooth, plus parts of the 2 teeth either side
of it. It's not "threaded" like a true hob, so gearing isn't used, but
the profile is a rack profile - thereby allowing the same cutter to be
used for all tooth counts.

There is a good article describing the parallel hob in Model mechanics
- may 1979 by Rex Tingey and i've seen it around more recently as
well.

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



On Jun 27, 1:15*pm, "DoN. Nichols" wrote:
On 2012-06-27, Des Bromilow wrote:


* * * * O.K. *What diameter hob? *How hardened? *And is this truly a
hob? *(Looks like an Acme thread which has been interrupted, and
requires being geared to the workpiece at the proper ratio for the
number of teeth desired on the workpiece.

* * * * If you mean a single path multi toothed cutter like a
conventional milling cutter, this is a gear tooth cutter, not a hob, and
is easier to use. *You need only the ability to turn it at the right
speed, and an indexing head to position the workpiece at the proper
number of locations for the teeth. *(However, these are made in sets,
and which one is used from the set is a function of how many teeth you
are cutting. *A true hob will cut the right shape for all pitches, while
the gear tooth cutter will only cut a range of teeth to a close
approximation of the needed shape. *The one for the smallest gear
(unlikely for a bull gear) covers only two or three tooth counts. *The
opposite extreme cuts something like from 180 teeth to a straight rack
gear.