cross posted to rcm. Thanks for letting us use the dropbox

Inspired by Anthony, here's another "How would you do it?"

A couple of years ago we got an email from a customer who wanted a =
special
part grounded. After taking one look at the pics I thought "No way!" =
The
part was impossible to grind, at least on our equipment. =20
I called the customer back and told him: "Sorry, but this is out of our
league" and quickly forgot the whole thing - or so I thought, because =
later
that day the light bulb inside my head actually began emitting light. A
flickering and shimmering glow, but still a light.

I had an idea!

http://www.metalworking.com/DropBox/ Search for "pigtail" (four files)=20


About the part:

The "pigtail" is a core for a mold, forming a helix hollow inside the
finished molded part.
The size is approx. 3" dia. at the base, the length is about 7" and
the tail is 3/4" thick. The last two inches of the tail has a taper.
The pigtail is bolted on the flange of a guide spindle, and runs inside=
a
large multi-thread bronze nut. When the core is pulled from the mold, =
the
threads provide the necessary rotating motion to unscrew the core.

So here's the deal:

The part was to be grounded on the cylindrical (white) part of the tail
roundness +- 0.0005" as it had to seal against the stripping plate.
The fillet at the base, and the tapered part should also have a "grind
quality" surface finish. Actual size was not too important.

There was a catch, though. The roundness of the tail was measured
perpendicular to the centerline of the helix, not the centerline of the =
part.

The part came from the customer hardned and pre-milled to about 0.05
oversize. Since they only had 3axis VMC, the part was milled from four =
sides
rotating the part 90 degrees each time. (I did suggest the part could be
milled to finished size, but they didn't think it was possible to achieve=
the
necessary finish/roundness.)

The grinder I used was a Jungner US-450 CNC with four axis - think of =
an
ordinary lathe, and swap X with Z & Y with X. Tool up&down =3D third =
axis [X]
Spindle =3D fourth axis [b] ) =20
=20
The Siemens 810 control only allow for three axis to move simultaneously.

To make an already too long story short; I somehow managed to solve the
task, but it did make my head hurt at times. =20

How would you have done it?

For those interested in the challenge, I'll post the solution on Monday.
(not like that spoil sport & teaser, Anthony) G =20
--=20

-JN-