Starting restoration of an IBM 2501 card reader for VCF 1130 system

STARTING RESTORATION OF THE VCF IBM 2501 CARD READER

The Vintage Computer Federation's InfoAge museum sent down the 2501 card reader and 1132 line printer that will work with their IBM 1130 of which I am currently wrapping up restoration. My first visual inspections suggest that the 1132 will be straightforward, just involving a ton of disassembly, frozen lubricant removal and loosening of all the myriad moving parts. The 2501 has some rust issues but still seemed feasible to be restored.

RUST IN VARIOUS LOCATIONS NEEDS TO BE REMOVED AND ADDRESSED

There was rusting on a few spots where it matters mechanically. Most importantly, there is a cylindrical rod that the output card hopper slides along as cards fill the hopper, but it is rusted and thus the slider barely can move over it. At worst case a replacement cylinder can be built, but I suspect I can knock down the rust and convert it leaving the surface good enough for operation. 

RUBBER BELTS AND OTHER PARTS SEEM IN VERY GOOD SHAPE

This reader uses several rubber drive belts to convert the motor rotation into rotation of various axles that move cards through the reader, motion both side to side and front to back. They appear to be in excellent condition, not worn and with plenty of spring left in the rubber. Other parts and wiring look undisturbed. 

TWO PLASTIC GEARS HAVE DISINTEGRATED

IBM chose to use some type of plastic, perhaps a nylon, for two gears in the machine. The rest are metal or Bakelite. The plastic gears are an outer ring that is fitted onto aluminum disks. The material chosen did not hold up well with age. Apparently key chemicals like plasticizers have evaporated with time, changing the characteristics of the material. 

What I found when I opened the 2501 was many fragments of gear teeth lying inside the machine, with just small arcs still connected to the aluminum disk for the output hopper gear. This gear turns a cam that moves the joggle plate side to side, keeping the cards separated as new cards are ejected from the reader into the hopper. 

A second gear is hooked to the outside of the CB (Circuit Breaker) wheel and drives the rollers that pull a card into the machine from the input hopper. IBM uses the term CB to mean multiple things. In this case, it means three magnetic coils that receive impulses from a permanent magnet glued to one point on the rotating aluminum disk. 

CBs are used by IBM to indicate a rotary position, either closing microswitches or in this case triggering a pulse in a coil. The speed of the 2501, at up to 1000 cards per minute, 16 2/3 rotations per second, dictates that the signals for the three coils (CB1, CB2 and CB3) are very short, in the range of 3-4 milliseconds duration and with on and off time requirements in the range of 100 microseconds. Coils with pulse shaper electronics easily achive these requirements, physical switches not so well. 

The teeth on the gear at the input hopper had turned to dust, rather than fragments, although I suspect that there are some small arcs of the teeth down inside the housing where I can't currently see. 

HELP FROM A MUSEUM IN EUROPE WHO HAVE A 2501 WITH THE SAME ISSUE

Friends at a museum in Europe who have a running 1130 system found the same gear disintegration in their 2501 reader. They created a 3D model for gear replacements and were able to achieve useful results for the input hopper gear using a 3D printer. 

Unfortunately, the output hopper gear has 211 teeth around a circumference of roughly 32 cm. The pitch between teeth is therefore about 1.5 millimeter. The precision of their 3D printer and the material used was not good enough to produce well shaped teeth spaced this closely together. The feature resolution needs to be about.1 mm, I suspect, for this to have a chance of working. 

I will see if I can find a 3D printing service that has a material and printing method that can give me a decent gear to use with the output hopper. The force of the cam moving the joggler plate back and forth won't be very high, but the teeth have to mesh well enough to turn the cam and not bind up.