[78-L] runout spirals

[Royal Pemberton]

I'd think that would be how a lot of eccentric grooves were cut, with the
disc offset.  The only mastering lathe I've ever seen, a Neumann AM 32,
actually had a latching arrangement on the underside of the turntable that
permitted offsetting it to permit cutting eccentric grooves.  (Once upon a
time, I tried to get the guy who owned the lathe to cut me a disc with an
eccentric groove at the end but he refused, citing the hassles of getting
the platter re-centred and perfectly balanced again....)

On Fri, Oct 8, 2010 at 5:40 PM, Michael Shoshani <mshoshani at sbcglobal.net>wrote:

> On Fri, 2010-10-08 at 08:53 -0700, DAVID BURNHAM wrote:
>
> > There are two possibilities - either the recording
> > stylus, after the music is finished, is activated by a cam to go through
> the
> > eccentric groove motion to create the trip groove, and then moved ahead a
> > millimetre or so and so activated again, or, the recording stylus
> disengages and
> > a separate cutter, mounted on the same assembly is brought down to
> engrave the
> > trip eccentric.
>
> I'm thinking the separate machine theory as well, but here's the kink in
> the works: the eccentric grooves on VEs are different sizes. If the dead
> wax is larger, the eccentric pair is really large, but if the dead wax
> is small, the eccentric pair shrinks. If they used a cam on one of their
> machines, it would have to be adjustable in some way.
>
> Early Capitols and I believe some early Deccas are cut with an eccentric
> runout spiral. This would indicate shifting the wax or lacquer disc
> somewhat while the spiral and locked groove were being cut, I think...
>
> MS
>
>
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