CUTTING THE DISK
Once started on its spiral course, a cutting stylus cannot be stopped
without ruining the disk. Everything must be pre-set and double-checked
beforehand, from the visual selection and flatness of the disc blank, to
the condition of the sapphire cutting stylus, chip suction and all the
audio connections and settings. An appropriate size recording disc blank
is chosen... usually 14" diameter for a 12" final disc size. A silent
groove test cut is made, outside the diameter of the finished disc. This
is examined under the microscope to check for correct groove size, and
sometimes played back to ensure that the noise level is appropriately low. Sometimes discs are rejected at this stage, or even a cutting stylus might be changed, before things are ready to begin the actual recording.
The vacuum pump is started, tape players are cued to the beginning of the
recording, the cutting turntable set rolling, and, when all is ready, the
stylus is carefully lowered to the record surface, the fast beginning
lead-in spiral is cut, the tape playback is started a turn or two after the
spiral has ceased, the audio feed to the disc recorder is enabled, and the
record is on its way. Depth of cut is periodically checked through the
microscope, and of course the volume levels must be watched even though
automatic variable pitch will protect against most instances of overcutting
to adjacent grooves, there are still the odd nasty surprises that get past
the tape mastering engineers. The running time must be checked at the 1/4,
1/2 and 3/4 way through, to ensure that the disc reaches the desired end
point necessary for standardization of the finished product.
At the end of the record, after about two blank revolutions, the final
spiral lead-out groove is made, again by speeding up the lead screw of the
cutting lathe, either automatically or manually, followed by a lock groove.
In earlier times, an eccentric lock groove was added on a special machine
designed for this purpose. The master is now done, except that it must be
visually examined very closely for flaws... once made, it is NEVER played.
For moving to the processing plant, masters are bolted by their center
holes into an elaborate box with separations that keep the actual surfaces
from touching; lacquer is extremely delicate and easily scratched.
(Masters are conveniently stamped or marked for identification in this
manner with a scratching stylus, the marks appearing on every finished
SPEEDS, GROOVES AND RECORD SIZES
There are only minor differences between records, other than the most
obvious of size and speed, from 7" 45 rpm through to the 16" 33 rpm
transcriptions once used by broadcasters. The greatest differences,
however, are found in the groove sizes. Coarse groove 16" radio
transcriptions used a slightly narrower and more closely packed groove than
the average 78 "standard", but it is played at 33 rpm. The groove used for
LP's and 45's is smaller still, and much more closely packed. The problems
of groove accuracy with LP's are greater in all respects, than with the old
larger groove, and for a while after the debut of the LP in 1948, there
were dire mutterings and groanings throughout the industry that small
groove cutting was all but impossible.
After unheralded agonies of experiment and slow experience, the cutting of
small grooves became less terrifying, and ultimately, no more trouble in
this area than the old, and with minor adjustments to stylus size and depth of cut, any sort of record may be cut on the same equipment.
The record mastering engineers are usually found in the studio environment
but the plating, pressing and manufacturing of the actual record is usually
done at another location. Once the finished lacquer is in its shipping box
we enter a new world, a world of more or less mass reproduction, where the
object is the making of many from one.