Around five years ago, I decided that I wanted to put together a disk cutting system. I started collecting and reading all related literature I could get my paws on, from the very beginning of disk recording to the present, in the form of books, manuals, journal and magazine articles, websites, and so on.
Eventually, I located a Fairchild model 199 lathe in the USA, which seemed like a decent start for the project. It started life many decades ago (late 30's as far as I could figure out) at the Fairchild Aerial Camera Corporation in New York. Fairchild Recording came a bit later than that. It was sold to a radio station in Grand Rapids, Michigan, where it saw plenty of use until it was considered obsolete. It then spent decades in storage at the radio station, until it was eventually sold some years ago to a man in Grand Rapids who sold it to a man in Florida, who sold it to me in 2015.
S/N 769
I got the lathe in the form of the mechanical assembly in a sort of crate, with a DIY cutterhead adaptor. There was no head or electronics with it. The drive to the platter comes from a big 60 Hz synchronous hysteresis motor, coupled to a gearbox/drive unit, on top of which the platter is bolted.
The motor is suspended on springs with damping material in them, and employs a rubber flexi-coupling to transmit the drive to the gearbox. I am located on the 50 Hz side of the pond, so the first thing I did was to put together a quartz-controlled, extremely stable and precise 60 Hz supply for the motor. This, along with the two-speed gearbox, can drive the platter at 33 1/3 rpm and 78 rpm. Changing the 60 Hz line frequency up or down can also derive 45 rpm, 16 rpm, and so on. Have not implemented this yet, but it is on my to-do list. For now 33 rpm is adequate for testing and further development.
I then got myself an RCA MI-4896 magnetic monophonic cutterhead to get the project going.
It unfortunately arrived broken. The coil seemed fine, but it was evidently out of whack mechanically. This could have been shipping damage, or just someone attempting to replace a blown coil and not knowing how to put it back together properly. Moral of the story, and advice to ebay sellers: Do not assume a cutter head is in working condition just because you can measure some DC resistance in the coil with an ohm-meter! If you are not able to properly test it, then it is safer to assume it is not functional.
I took it apart and rebuilt it. All the bits were there, but it needed a careful alignment. After that it worked great. These are nice little heads if you're into the vintage sound of the early days of electric recording. Think of early blues up until the 50's or so, rock'n'roll, etc.
I had some choice of power amplifiers to try out, but needed the RIAA pre-emphasis. I built some simple passive units based on the Lipshitz and Hagerman articles.
My playback equipment and Mastering chain put out very high signal levels, while several of my power amplifiers expect a 0.7Vrms input level. The attenuation from the passive RIAA pre-emphasis circuit does a great job of matching the levels.
I built a big, heavy and beautiful wooden cabinet for the lathe, put together a heat lamp assembly and a microscope, and not having a chip suction system ready yet, I started off with impressing (embossing) on polycarbonate blanks.
Of course, to properly align the stylus with the centerline of the record, I had to make a new adapter to compensate for the drastic change in angle of cut.
Although this lathe is around 80 years old and saw heavy use in its youth, it is in remarkably good condition. This is due to the exceptional design, use of high quality materials throughout, and excellent machining. A lot of parts are made of stainless steel, which prevented corrosion during the decades in storage. There was plenty of grime that had to be carefully cleaned away, and the entire machine was in a desperate need of proper lubrication.
Then I started noting down the problems. The first serious problem was a terrible noise coming from the gearbox and the second problem was a massive platter run-out.
I started by removing the platter and realising that the noise source was inside the gearbox! Horror! No service manual there, no pictures online, nobody I could find with experience working on these gearboxes! All I knew was that it is a fairly complicated machine with helically cut gears, worm-gear drive, numerous oil seals, a gear change and a clutch. In the service manual of a similar Fairchild lathe there was mention of a ball-race step-up... The drive unit is Fairchild model 824, by the way.
Luckily, I have plenty of experience working on old machines, as I used to maintain, repair, modify and convert vintage tour vans for bands, mobile studios and so on. I also drive, maintain and repair this 1979 Bedford, which has driven me and other musicians all across Europe for several years...
So I took a deep breath and pulled it apart! I was going completely in the dark, trying to figure out the multiple adjusters, bearings, ball races, seals, etc. I was glad to see that the over-engineering extends into the gearbox and that nothing was broken or worn too bad. The problem was that one of the previous owners neglected the bothersome routine lubrication procedure and damaged some races and thrust washers. I measured them carefully, got replacements and put it back together.
I'm not good at shooting pictures while I'm working on something because I get absorbed in what I'm doing, so there's no pictures of the insides of the gearbox. The surgery went well and the noise is gone. I re-aligned the motor and rubber coupling and it runs nice and smooth.
Next up was the run-out.
The gearbox shaft was the first point of call. All good there, so the next tricky part was mounting the flange for the platter on the shaft. This flange has an unusual adjustment, with a half-circular key floating in a half-circular slot on the shaft, with an allen screw on the side to secure adjustment
I managed to get the flange aligned to the point of no visible deflection on the dial gauge in any direction.
Then came the platter, which is a 16lbs cast alloy affair. For some reason, it was not straight on the straight flange. It appears the the top face is not 100% parallel to the bottom face, causing a run-out there too. While planing the faces accurately and then cutting a new spiral on top would be an option, I decided to proceed with a different idea. Inspired by the adjustability of the platter on more modern lathes, I drilled and tapped three equidistant threaded holes for adjusters on the platter!
This did the trick and I got the run-out to +/- 0.9 mil at 16".
The rest is due to an uneven top face, so machining the platter in the future might be a good idea. Most blanks, especially plastics, exhibit far more run-out though, not sure if it is really worth the effort to improve the platter further. More soon....
Statistics: Posted by jesusfwrl — Mon Nov 23, 2015 11:47 am