Re: [ARSCLIST] AW: [ARSCLIST] microscope for checking groove wear

["Copeland, Peter" <Peter.Copeland@xxxxx>]

Before I joined the British Library Sound Archive, I was a disc-cutting
engineer, and several thoughts come to mind.
(1) The microscope I used was supplied on a Presto disc-cutting machine.
The idea was to see the disc while it was actually on the turntable
(which is surely the best way to handle a disc record in these
circumstances)! There was a pillar on the corner of the lathe deck, and
the microscope was attached to this through a V-link so it could be
moved manually to any part of the disc surface, whilst being held at a
constant height so things were more-or-less in focus at any place.
(2) The microscope was made in 78 days, and had forty-diameter
magnification. With microgroove I found this wasn't powerful enough; but
by cannabalising two microscopes and adding an extra part, it proved
possible to make an eighty-diameter microscope.
(3) However this wasn't sufficient to show the curvature at the bottom
of the groove. As it was a near point-source of light, one saw a bright
line at the bottom of the groove. I have found the only way of
approximating this is to play the record with different-sized styli, and
listen for the characteristic sounds of "groove-bottoming."
(4) Illumination was important, and I found two methods were vital. For
the operation of examining the groove as it was being cut (mainly to
check the variable groove-pitch was sufficient for the level of
modulation), a small torch bulb in a parabolic reflector was attached to
the microscope itself, bringing light sufficient to fill the whole field
of view.
(5) But for examining damage, I recommend (a) greater magnification, and
(b) a more widely-variable source of light. I achieved the latter by
means of an "Anglepoise" lamp, which I moved all around the turntable to
show clearly what I was looking for. Individual scratches and continuous
groove-deformation could be shown this way, and a "normal" disc was also
kept nearby so that, by substituting an unworn disc, the difference(s)
became clear.
Peter Copeland 

-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:ARSCLIST@xxxxxxx] On Behalf Of Otto Striebel
Sent: 10 May 2005 16:54
To: ARSCLIST@xxxxxxxxxxxx
Subject: [ARSCLIST] AW: [ARSCLIST] microscope for checking groove wear

Hello.

I'm also interested in a microscope to check the groove diameter.
However, it shouldn't be too expensive.
Yours sincerely,
Otto Striebel
Kirchheim, Germany

-----Ursprungliche Nachricht-----
Von: Association for Recorded Sound Discussion List
[mailto:ARSCLIST@xxxxxxx]Im Auftrag von Erik Dix
Gesendet: Donnerstag, 5. Mai 2005 16:36
An: ARSCLIST@xxxxxxxxxxxx
Betreff: [ARSCLIST] microscope for checking groove wear

Hi!

Could anybody recommend a microscope for checking groove wear!
Erik Dix

Notre Dame Archives

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