[78-L] runout spirals

[Milan Milovanovic]

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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