On 2010-07-28, Brian Lawson wrote:
On Wed, 28 Jul 2010 08:20:15 -0500, Ignoramus6705
wrote:

On 2010-07-28, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus8984 fired this volley in
:

I need to copy a sprocket from an old motorcycle for a friend of
mine. It has a conical hub.


My first two questions would be: "Is the hub conical simply as a
casting/forging expediency?", and (if it's tapered on the i.d.) "could I
cut that with a tapered reamer instead of milling the hole?"

No, it is tapered so that the sprocket would lock on the hub.

It is from some old Indian motorcycle. I am not a motorcycle guy and
have no knowledge or interest in them. But my friend does. This is
perhaps a 90 year old sprocket that needs to be reproduced. I would
guess that the angle on it is not standard.

i


Hey Iggy,

In a machine/tool shop, they would probably do the "cone"as you have
done so far, leaving a few thou for finish, then on a Deckel SO (or
similar) would make a tapered carbide cutter, possibly just grind a
"D" type (or even 2 or 4 flutes) to the angle required and then use
that cutter and do the finish circular interpolation using it to give
a "finish" surface.

As this sounds like a kinda small workpiece, or at least if the "hole"
is less than 2 inches, you might even try using a smallish grinding
stone/wheel cut to the correct angle and chucked in a Dremel clamped
to the quill or spindle of the Bridgeport. A "high-speed" attachment
for a mill is a handy thing to have anyway.

I milled some cones yesterday (in wax), with a ball mill.

My procedure for milling a cone involves, first, roughing out of the
area, and second, doing many circular passes through the material. The
number of passes depends on my parameter fine_finish_zstep.

I milled a cone that was 1 inch deep, and was 1.2 inches diameter on
top and 0.6 inches at the bottom.

For fine_finish_step I picked 0.01, so my mill did 100 passes, with a
0.25" ball end mill, going 0.01" deeper every time.

The result was smooth as if it was turned on a lathe.

Roughing out was relatively quick. I had to stand by with a vacuum to
remove wax chips.

Finishing took quite a while, since I selected a slow feed
speed. About 15 minutes IIRC. It was boring (as in "not fun"), so I
went inside and watched it via the netcam.

ps....are you thinking of attending IMTS2010 at the McCormick?
http://www.imts.com/
It's on from September 13 to 18. I might go for one or two days.

Lemme know if you are interested.

If I get time to go, definitely.

i