> (NOTE: I got this as direct mail from John. It was apparently addressed
> to pwcs!phile@hoosier.cs.utah.edu. I did not get the one he sent to
> british-cars@autox.team.net nor any of my mail from any mailing list.
Actually, I didn't send it to the list, since this "Is so! Is NOT!" stuff
might be boring to some...
> > > > Gears are easy - you can cut them on most lathes, without any CNC.
> > > > Cams, cranks, & so on are much tougher.
> I wrote > >
> > > You can cut gear BLANKS on a regular lathe.
> > > To cut the teeth, you need a hob.
> John R. Lupien writes >
> > I made a nice straight-cut gear on a lathe, it really was easy.
> > Cutting the blank is the hardest part. To cut the teeth, you use
> > this many-toothed rotary cutting device that clamps onto the
> > screw thread drive. They have both straight-cut and helical
> > tools for this, I think, though I have only used the straight-cut
> > version.
> That is a hob. According to my dictionary: "A cutting tool used for
> cutting the teeth of worm wheels or gear wheels."
It's not a hob. I looked it up in my machine tool catalog, and it's
called a gear-cutter ("involute", I think). And the piece is rotating,
too - not just the tool. It's one of the coolest things to watch running,
short of the multi-tool CNC machines. The cutter and the gear blank
rotate, and the cutter moves sideways, making contact with the blank
at the edge. Each tooth of the cutter makes a small cut each time around,
until it is fully engaged and just chopping its way through. Finally the
tool comes out the other side, and you have a complete gear in about the
same time it would take to cut one tooth on a mill.
> "Most lathes" are not going to have a hob attachment. Where were you
> working that had one of these? I have never seen a hob attachment on a
> regular lathe, but then, I have only worked in about 5 shops and seen a
> maybe 50 while working in machine-tool sales.
That was 2.86 lab at MIT - and the lathes were really quite regular. They
had one fancy one that was basically the top-of-the-line not-quite-cnc,
but us student types didn't get to use it. The rest of the lathes were
pretty basic - I didn't notice anything that wasn't on the lathes in
the 2.76 lab (which was all really "run-of-the-mill").
> I can envision cutting straight-cut gears on a lathe by cutting each tooth
> with the lathe spindle not turning.
Sounds like a minor nightmare.
--
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John R. Lupien
lupienj@wal.hp.com
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