On Sat, 09 Apr 2011 12:41:01 -0400, Ed Huntress wrote:

"Tim Wescott" wrote in message
...
On Sat, 09 Apr 2011 00:32:29 -0400, Ed Huntress wrote:

"Tim Wescott" wrote in message
...
On Fri, 08 Apr 2011 23:16:17 -0400, Spehro Pefhany wrote:

On Fri, 08 Apr 2011 23:08:55 -0400, Spehro Pefhany
wrote:

On Fri, 08 Apr 2011 21:38:25 -0500, the renowned Tim Wescott
wrote:

I want to make a bunch of identical molds, for 3/4" diameter model
airplane wheels.

I'm envisioning a tool that's 3/8" across, that I just sharpen up,
grit my teeth, and push into a spinning piece of aluminum to make
my desired profile.

Is this a sensible thing to consider? Is there some other way
(short of CNC machining) to easily duplicate cavities in the ends
of a bunch of aluminum tubes?

Hobbing?

P.S. Not the gear-making process, this one:

http://tinyurl.com/hobbing

Well, the cavity is cylindrically symmetrical, so I'm not sure that
"hobbing" is the right term.

It's probably been a screw machine operation since 1920, or at least
some sort of tracing operation.

Sigh -- I'm always behind the curve.

I must be dull tonight, but I can't visualize what you're doing. Are
you talking about some kind of forming in the axis of a spinning tube,
or turning the outside diameter to a profile?


Let me know if you can see this, it should explain:

http://www.hippocketaeronautics.com/...rum/index.php?
action=dlattach;topic=5869.0;attach=53766;image

Sorry, that isn't working for me. Or I don't know how to get there.

I'll wait and see what others come up with. It sounds like you want to
do some kind of form-tool operation, in which case, as someone
mentioned, the key is the length of contact for the cutting edge. I've
seen some really long ones -- the whole length of a chess piece, for
example -- performed on South Bend 10" lathes with complete success.

But I may be on the wrong track. I'll wait.

Is this better?

http://www.wescottdesign.com/temp/wheel.jpg

It's a Smithy lathe, and a form tool is what I was thinking about, except
that instead of applying it radially it'd be applied axially -- which
means that the ratio of cutting speeds from inside to outside would be
huge.

I actually sorta-kinda used a forming tool for the tire profile, then cut
the hub by hand -- I just want something that'll do a more consistent job
of it.

--
http://www.wescottdesign.com