[78-L] runout spirals

[Michael Biel]

From: Royal Pemberton <ampex354 at gmail.com>


> No, those are called drive pin holes, and served only to
> prevent slippage of discs while cutting.

If you tried cutting a lead out circle with the disc in a driving hole
you will find that the swing of the eccentric is HUGE!!!!  Plus the
cutting of eccentric lead outs predates the use of lacquers by well over
a decade.  And modern lacquers no longer have the driving holes because
modern lathes use vacuum suction to hold the disc to the turntable.

Mike Biel  mbiel at mbiel.com  


On Sat, Oct 9, 2010 at 5:05 AM, Milan Milovanovic <
milanpmilovanovic4 at gmail.com> wrote:

> Are those eccentric grooves were cut by placing lacquer in those additional
> holes (1 or 3 of them) used for stabilizing locking blanks onto lathe mat
> when cutting? You can put cutting needle anywhere then and make just one
> simple revolution, and voila...
>
> Just a thought...
>
>
> ----- Original Message -----
> From: "Royal Pemberton" <ampex354 at gmail.com>
> To: "78-L Mail List" <78-l at klickitat.78online.com>
> Sent: Friday, October 08, 2010 7:06 PM
> Subject: Re: [78-L] runout spirals
>
>
> > 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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