For coarse groove recording, the stylus was often mounted with a slight mechanical bias toward the center of the record. The top of the groove is supposed to measure not less than 4 mils across, for a recording to be played with a 2.5 mil stylus, and in the case of LP's played with a 1 mil stylus, no less than 2 mils across at the top. Connected to a power supply with adjustable current and metering, is used to bring the cutting stylus to a carefully controlled even temperature. The hot stylus momentarily softens the lacquer surface of the recording disc while the groove is being cut. The lacquer thus offers less resistance to the cutting process, the cut is smoother with less distortion, and the necessity for diameter equalization is virtually eliminated, being reduced to about a 2dB difference between the outside to inside of a disc.
Habits are hard to break.
More blemishes and defects produced lower quality levels that sold for less and less down to the level of the home recording user. Needless to say, for the making of commercial pressed records or radio transcriptions there was only one standard - the best that can be had for the purpose. T he mastering engineer controls all aspects of the overhead cutting mechanism, which extends from the outside edge, across the record, to the center pin, like a bridge over water, and from which the recording head with its stylus is lowered to the record surface. The spiraling grooves are cut by moving the head very slowly, across this bridge, usually by a type of screw feed. A disc recorder working upon a blank disk, has no such thing to guide it's motion, and so it must be mechanically moved by a special mechanism to cut spiral grooves.