Thursday, August 19, 2010
How a vinyl disc is produced or the making of a record
Are you sitting comfortably?
It all starts with the disc recorder or "lathe" as it is often referred to, an amazing piece of equipment designed with a slowly rotating feed screw mechanism and carriage to move a cutting head across the radius of the disc. The accurately shaped cutting stylus, mounted in the head, cuts a precise spiral groove across a flat lacquer coated aluminum disc (acetate) spinning at an exact speed of 33-1/3, 45, or in the old days, 78.26 revolutions per minute, the standard phonograph operating speeds.
Next see's the cutting head installed on the lathe, this is simply a phonograph pickup in reverse, that is, feed audio in and get mechanical motion out. Other than Dits greater size, the specially shaped cutting stylus, and the feed screw mechanism which moves the head across the record to make the spiral groove, the internal workings are very similar. The recording stylus is probably the most important component of the recording process, and was probably first used by Edison in 1877.
Diamond is not a good material for a cutting stylus, but is excellent as a reproducing stylus. Home cutting styli were commonly made of a steel alloy because it was inexpensive to manufacture but most cutting styli for professional use are made of corundum, better known as sapphire which will outlast a diamond and produce superior recordings. Since those early recordings on wax, recording blanks have been called by various names including instantaneous discs, lacquers, acetates, soft-cuts and others. The most accurate is probably "lacquer" because of the fact that they are lacquer coated with a compound of cellulose nitrate, and acetate had little to do with it, although it has become a common name for a lacquer coated disc, and many professionals still use the term "acetate".
The phrase "waxing," still persists to day even though the old solid block of wax were in use until not long before World War II. Before there was no magnetic tape and the recordings had to be cut originally on huge thick blocks of warmed, essentially beeswax. The final product before "processing" became a single lacquered disk onto which the actual recording grooves were cut. different grades of "acetates" were offered by the manufacturers, distinguished by the evenness of coating and thickness of the metal itself. Simply explained, all the discs of a given grade started through the manufacturing process the same way, but subsequent inspection determined the quality level that the disk met before it was shipped out for use. Before setting off on its spiral course, everything must be pre-set and double-checked, 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. Once it's underway a cutting stylus cannot be stopped without ruining the disk! 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.
It this point the vacuum pump is started, tape players are cued to the beginning of the recording, the cutting turntable set rolling and now the stylus is carefully lowered to the record surface. First, the fast beginning lead-in spiral is cut, the tape playback is started a turn or two after the spiral has ceased and the audio feed to the disc recorder is enabled. 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. 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 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 and is visually examined very closely for flaws... once made the master is never played. for moving, the masters are bolted by their center holes into a complicated box of separations that keep the actual surfaces from touching, the lacquer is extremely delicate and easily scratched.
There are only minor differences between records, other than the most obvious of size and speed, from 7" 45 rpm through to the 12" 33 rpm. 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 than with the old larger groove, and for a while after the first LP's in 1948 it was reported throughout the industry that small groove cutting was all but impossible. After months of experimenting the cutting of small grooves became less hassle and no more trouble in this area than the wider groove process. With minor adjustments to stylus size and depth of cut any record type could be cut on the same equipment. Producing a metal press that will actually mold records from shellac or vinyl is a multiple plating process.
Depositing metal upon metal by means of an electric current that transfers metal through a plating solution directly to the actual surface being plated. At this point record making is surrounded by tanks. Rows and rows of containers filled with multi coloured liquids, some steaming, some sloshing about, as objects are swished through the depths. To make an actual metal impression the lacquer must either flow on the metal and let it harden or plate it on cold. The first process obviously being impossible (lacquer is a soft, highly inflammable plastic!), some form of plating is the only answer. But how do you plate metal onto a non-metal? A number of methods have been used. The oldest, when master records were cut into wax blocks, was to apply an extremely thin coating of graphite, a form of carbon that we know as pencil lead, which conducts electricity. To this coating, thin enough not to disturb the record groove shape unduly, one could actually plate metal, which would take on the shape of the record grooves. When enough metal had been backed up on the plating, it was an easy matter to strip it from the wax and the graphite, leaving a mold of metal. Three ways are used to get the first microscopic layer of metal onto the lacquer. Silver spray is the newest and trickiest and also the silver pan bath is still used, similar in its chemistry; it takes longer, and is not as accurate . Lacquers are treated in a different way, to give metal coatings at first only a molecule or so thick.
The most dazzling to watch involves silver nitrate and a simple spray gun. The lacquer surface is "sensitized" by being dipped into a solution of stannous chloride which is washed off in a water spray, leaving a very thin coating. Silver nitrate solution is sprayed at the disk and the black becomes a mirror of silver in seconds. Silver has been deposited in an extremely thin layer by chemical (replacement) action, the stannous chloride acting as a catalyst to promote the process. The newly silvered disk is washed and moves on to its next treatment. The next objective is to build up a solid metal backing on the thin silver coat. This may be confusing, since this "backing" is actually being deposited on the front of the original disk. Remember, that we are making a negative mold, its surface now of silver, in direct contact with the lacquer surface and facing away from us as we look at the record. We are really looking at the silver from the rear, and we are about to add more metal to that rear in order to stiffen it. The original record will eventually be stripped away, leaving the other side of the silver, the facing-down side, as the mold. The beginning of the build-up of the metal backing support, a layer of very fine-grained and delicate copper or sometimes nickel, is laid down slowly on the silver surface just produced. It's fine-grained in order so not to disturb the tiny groove patterns and to hold them accurately in place.
After this, a more coarse grained metal can be piled on, although in some plants, another layer of fine grained "pre-plating" is added first. The coarse coating is desirably much faster, since at the slow fine-grain pre plating speed, it may take weeks to build up a strong enough layer of metal. One company used special rotating disk anodes that swish around close to the surface of the metal record and do the plating job to required thickness in a few hours. Other much slower systems use the usual immersion tanks with moving arms to swish the contents about. Enough metal is put on the back of the silver surface to support it rigidly. and with a quick blow of a special hammer and with a shaking of the inserting tool, the entire silver-copper mold breaks free from the lacquer, and we have a negative in metal, the back side or down-surface of the silver a mirror-image the original grooves. The lacquer is usually damaged in this separating process and cannot be used again; so the new metal negative, or "matrix", is now the only form in which the grooves exist. Being a negative, the grooves become sharp ridges with flat valleys between. This metal negative or "matrix" can now be used to stamp out actual records! Since it is now the only existing copy of the original lacquer disc, in most cases it is used to produce a "mother", a positive metal record that can actually be played for testing purposes. Playing is not this mother's destined role and instead, the mother is submitted to another plating operation much like the first, ending in another metal negative which is the desired "stamper". Since the mother, unlike the fragile lacquer original, is made of metal, it can be re-plated many times over, producing negative after negative in metal, all identical with the first.
We now have a source of negative offspring stampers, each of which can press out as many as a thousand or so actual finished records. Multiple mothers can be made from the original metal matrix so multiple identical mothers can be sent to other pressing plants or countries for their production requirements, and thus huge quantities of records can be produced in a very short time if need be, all with exactly the same quality level of the release pressings in the originating country or plant. The first step in preparing for the creation of the mother is to remove the silver that now contains the direct groove Impression.. Removing the silver coating is necessary because it would quickly oxidize and corrode in the air. Fortunately it is a molecule-thin coating, and the underlying harder metal has virtually the same sharp image as the original. A swish or two of chromic acid takes the silver away faster than it was deposited by spray in the first place. With the silver off but the groove image still "metalized" in the negative matrix, the whole plating process is repeated to re-create a new image. Before plating, a separating solution is applied to the surface, so that, though metal will plate on metal, it can be stripped off later on, otherwise the entire thing would become a useless solid metal block. Next, a hard but ultra-thin chrome surface must be plated on and next the hole in the middle, plus the stamper's rear side, which must be shaved to the right thickness to fit the press and the outside edge which must be trimmed to size. The rear surface is machined away in a lathe operation where a precision gouge scrapes a spiral track from the outside of the back, right to the inside, shaving off all the irregularities, leaving a mirror-bright flat backside. The edges trimmed, the stamper then goes to the centering machine. As soon as the master has its hole, it loses it. Another punch knocks out a larger area, usually a couple of inches in circumference from the middle to fit the center of the press. But the disk's position is exactly determined by the small hole, and so the essential information is preserved, the final hole in the record to be made in the actual pressing according to it.
After the previous steps that occur between the original recording and the final metal negative stamper disk comes the final operation of making of the actual record. The basic press structure is precisely what is needed for record making... two similar molds, both heated, mounted face to face with a hinge at the rear so that the machine opens up facing you. Enlarge these two molds to record size; to hold two record stamper disks, one below and one above (fastened in by their centers and around the edges), and you have the beginnings of a record press behind each stamper comes a sudden heat, using super-heated steam at three hundred degrees, then quick cooling by cold water, all of which must be controlled by the opening and shutting of appropriate valves - and automatically, since no human operator could maintain the exact desired cycle of hot and cold that produces the perfect record. The easiest record to make and the most common is the solid disk, of a single material all the way through, though the more complex records, such as Columbia's old laminated disk, go through the same presses. Record and label are bonded together in the pressing. The operator of a pressing machine has beside him a "hot tray" on which is placed a dozen or so rectangular blocks of material, (shellac or vinyl) about half the area and two or three times the thickness of the final record. The biscuits are softened up on the hot plate until they are of the consistency of a soggy piece of fried mush, just about movable in one piece, and no more. With the press open, first a label, then a biscuit, then another label is placed in the press, and the top lowered. The automatic system then takes over unobtrusively; steam heats and flows the plastic material into every tiny groove; at the predetermined moment it is replaced by water, and the record is instantly hardened. The record is lifted out, and the next one is ready to go in.
After coming out of the hot press the newly made record has its ragged edge neatly trimmed by a circular cutting device and then passed on for inspection. Records are rejected by visual inspection and by actual playing checks. A significant quantity are rejected - large bins of rejects, returns and cut-outs wait to be fed to the elaborate machinery that reduces these masses of unsatisfactory disks to chunks, and then to powder for recycling into more records. Visual inspection is done by workers who look closely at every disk that comes to them on conveyer belts, sorting out the rejects. The supplementary playing-out-loud of a sample record every so often catches most faults that may have developed in a stamper before it has pressed too many bad discs.
... an always interesting essay.
Posted by twogoodears at 8/19/2010 11:42:00 AM