In response to Mark Buckland's posting regarding disc restoration
[180120 MMDigest], particularly the application of heat to the
centre, I also had read of this method somewhere along the line,
and though it went against the grain for what I understand,
I gave it a go (24.5 Polyphon).

I should have known better.  The raised area of a disc is caused
by radial stress, be it through incorrect height of the drive dog on
a smaller machine, or centre post on a larger, and or it's relative
position to the pressure arm.

When heat (even gentle) is applied to the central area of the disc,
it expands rapidly.  As the heat travels through the steel, expansion
at the point of stress produces a variable where the steel has been
work hardened.  In the case of the disc I was attempting to flatten,
the raised centre (lifted due to stress mentioned) lost its temper,
distorted considerably and _popped up_ like a perfect little dome,
rendering the disc useless.

At this moment I am working on a batch of 26.5 Monopol discs that
are tired, to say the least, but thankfully are salvageable.  There
is a consistent distortion around the periphery where the drive holes
are located, brought about by incorrect roller pressure, that's an
easy fix.  I have a pair of flat-faced long-nose pliers I use as a
hand vise, and I press the affected area.  It's a 5-minute job and
perform a second run, pulling the disc through the closed pliers to
smooth out any ripples.

There is also distortion on this batch of discs at the point of contact
with the first roller on the pressure arm nearest the centre post.  As
this stress line radiates, it affects the first six linear runs of bass
projections, so the disc needs flattening back into a useable manner.

With the disc face down on a flat surface, use a broad-tipped flat
screwdriver to press out the distortion.  Care must be taken not to
tap the end of the screwdriver or definite punch marks and further
damage will ensue, especially on softer discs.  It's advisable to
grind a broad flat on an old screwdriver especially for this purpose.
The rule is 'press, don't punch!'

When we come to the light, non-radial creases that have occurred
through carelessness at some point, the following method applies from
my own experience with discs for large upright players.

Take the disc between thumb and forefingers of each hand and give it
a light wobble-board type flexing.  Spin it by 90 degrees and repeat.
With a little practice, you soon get the knack wherein you can 'feel'
the stress line.  Due to a difference in the flex, your hands will soon
to engage the optimum position.

A gentle but exaggerated wobble and/or distortion of the disc in the
opposite direction to the distortion will improve the imperfection and
hopefully the smooth operation of the disc.  There will still be a mark
on the disc, put you will feel the stress being dissipated and a visual
improvement, will soon become apparent.  The bigger the arc, the less
pronounced the distortion, the easier to ease it out.

Smaller creases closer to the periphery can also be removed by feel,
manipulating outstretched fingers to support the disc on the radial
outside of the crease.  With disc facing down and thumbs on the inside
periphery, the weight of the disc bears down on the point of stress.
A gentle shake as the disc bears down and an increase in pressure with
the thumb can relieve the distortion sufficiently to bring the disc
back into serviceable condition.

This method does not work for concentric radial stress rings.  The
method is also a little 'hit and miss' but with the ratio something
like 70:30 in favour, to my reasoning, it's worth it.  The misses are
more likely, the thinner the gauge of disc material.

While all this may now be as clear as mud, I suggest to anyone with
a pile of damaged old discs to take a fresh look, flex them, move them,
feel them and play with them; they are never going to be mint, but who
cares if they can be played and enjoyed once more.  If you have a disc
that you just know is unlikely to play again, practice your technique.

On closing, it always pays to finish off with a little detailing.
To avoid any extraneous noise remove even a light dusting of red rust
with a soft wire brush that you might use on suede shoes, and 0000
gauge steel wool on the flat, with extra care where the drive holes
are located, so they pass with ease over the dishing rollers.

While I always take care to preserve as much of the transfer detail as
possible, I have found that others before me have scratched titles on
the rear in the Stop/Start position, when the transfer is in danger of
being lost.  Having neither time nor inclination to restore the discs
to pristine aesthetic order, I use an indelible felt marker pen.

A product called "Wood Silk," a wood polish without water or silicone,
is worth its weight in gold -- use it on both dishing and pressure
rollers, the flat of the disc and the drive area of the projection
side.  The quality of operation is vastly improved.  It works a treat
on the case as well.

Mark Singleton

 [ The complete name seems to be "Aristowax Wood Silk Advanced Aerosol
 [ Fine Furniture Polish with Beeswax No Silicone"  -- Robbie