Hi all,

Not having immediate success (but by no means having tapped out
all available vendors or sources yet, either) I have not yet found
suitable gears to feed the quick change gear box on the Hendey.

I did in the course of poking through some of my boxes come
across a 3"OD x 6" long hunk of 6061-T6 aluminum (aluminium for
those across the pond).

This is where the insanity comes in:

I have two 72T 14DP gears. If I had two 36T 14DP gears, I should
in theory be able to generate all the speeds I need for my gearbox.
If I had 3 or 4, I'd even have extras for idlers. These are 14.5 deg.
pressure angle gears. I also have a 90T gear to also use for idlers.

I've studied John Stevenson's document at
http://www.metalwebnews.com/howto/gear/gear1.html

and see he never posted data there for 14.5 deg. PA gears, though a
wander through Google Groups shows that he's supplied odd numbers
here and there for individual responses. Does anyone know of a
source for similar data to his "table 2" for 14.5 PA gears?

But his technique also got me thinking:

All I really need to create approximate gears is a form tool, it
doesn't have to be one for horizontal milling, be it disk type or
fly cutter type. Why not a single lip milling cutter, aka, form
ground D-bit? Glenn Ashmore just made a simple taper one for his
grinding fixture with apparent success. Probably grind one up out
of a broken tap or drill bit, and use the ultimate reference for
tooth form, one of the tooth spaces of the existing gears. Chuck
the bit of rod in a hand-held drill, and rotate it against the
grinding wheel. Once happy with the form as compared with the
master gear, grind off half to form the cutter.

Next, drill and bore my blank for 1", and turn to 2.571 OD. Not
likely I'll hit either exact, but hopefully well enough for this
exercise. And by doing them both in one set-up, I'll not be relying
on my decrepit 3-jaw for accuracy.

Once removed, mount the blank on a 1" arbor. Will probably use one
or both of a filed keyway and/or a tapped hole for a set screw (or
even 2?). Mount 1" arbor in boring bar holder, on center line, of
my 200 series tool post. On the other end, mount keyed 72T gear to
use as an index with an improvised locating pin. Use the boring bar
clamp to resist rotation and not put too much load on the pin.
Either buy or improvise an end mill holder (4MT), and mount the cutter
in the spindle. Set the blank axis at the proper final gear depth.
Set a feed stop. Feed the blank past the cutter with the crossfeed,
increasing infeed in several passes until I reach the stop for each
tooth space, then re-index.

The big advantage of this setup would be that it does not require
either a milling machine or a milling adapter for the lathe, just the
boring bar holder, and other pieces I already have on hand.

Possible pitfalls: Running out of crossfeed distance to finish across
the gearblank faces. Not having enough room to use the 72T gear
without it hitting the saddle as I infeed. Losing index and messing
up gear spacing, either by bending the locating pin or poor clamping
or rotating the index gear or the gear blank on the arbor. Mangling
or breaking the cutter with poor selection of milling feeds or speeds.
Trying to cut without noticing the cutter has become dull (how do you
resharpen a D-bit form cutter, anyway?). Mangling my cutter beyond
repair before I get all the blanks cut. Before I get any cut. Before
I get all the tooth spaces on one gear cut. Better to risk everything
and cut all the blanks at once? Or better to risk the cutting edge
dulling and cutting one blank at a time? Maybe one to learn on, then
the rest as a group? I should at least have enough stock for two or
three tries, depending on how many gears I want to end up with.
Given that I'll be cutting aluminum and not steel or cast iron, am I
likely to have sufficient rigidity and cutter life to complete this?
Any other obvious or not-so-obvious pitfalls I'm overlooking?

And last but not least, am I likely to run into problems running
6061 gears with cast iron gears in the gearbox feed train?

So give it to me straight, guys, how insane am I to even consider
this? I note that broken drill bits are essentially free, and the
chunk of 6061 cost me maybe $3 at a flea market. Have I mentioned
yet that this would be my first project on the lathe?

Thanks in advance,
--Glenn Lyford