Injection molding and potential uses in the 1130 project

I have been taking training classes at my local hackerspace (Techshop San Jose) in order to make use of various machines and processes to complete parts of the project. The 1130 has a number of plastic parts that I could replicate using various methods. I have used the 3D printers to build some switch handles but when the surface has to be smooth and high gloss, additional work is needed as the printed results themselves are not satisfactory.

In addition, there are some parts that are larger, more visible and have to accommodate higher forces during operation. For example, the knobs on either side of the console printer (typewriter), which are used to roll the platen when you add paper or adjust the current typing line, are glossy, fairly large and have some knurl-like detailing around the edges.

To investigate alternatives, I signed up for some plastic fabrication courses, which included an injection molding session last night. The shop has a low end machine, which costs a mere $30,000 as it is mainly manually operated and suitable for low volumes and might be run as fast as 5 moldings per minute only if you had a crew of people and several copies of your mold. This melts the thermoplastics at temperatures up to 750 degrees F, injects them into an aluminum or steel mold at 7,000 psi while the mold is clamped together by up to 20 tons of pressure.

Further, a mold has to be milled out of aluminum (relatively inexpensive but limited to only 10-20,000 cycles of use before it is too deformed) or steel. This involves using the 3D modeling tool to design a mold and the CNC milling machine to cut it. I am up to speed on the tool, Autodesk Inventor, although the mold specific functions are new to me. However, I have a few classes to complete before I can use the Tormak CNC milling machine to fabricate my molds - these are scheduled for the last week of this month.

The typewriter knobs and some buttons that are on the faceplate of the typewriter enclosure could be produced by this process, with a glossy finish produced through polishing of my mold after the CNC mill has cut it. I would use colored ABS plastic in the medium blue color that IBM chose for the 1130. I don't see any big risks here, it will only require time and effort to yield the parts.

The internal disk drive in the 1130 has a blue plastic handle used to open and close the drive - I potentially could produce such a handle although its size exceeds the mold capacity of the injection molding machine. I would need to join several pieces together - not sure how feasible that is - but it is a possible "flourish" for the project.

Another area where I could improve the project and also help some real 1130 restorations is by producing the special Selectric type ball with the character arrangements IBM used for the 1130. There are two, ignoring various non-English variants, the normal ball and a ball used when running the APL software on the machine. My system uses the Selectric III style balls - 24 rotary positions and four tilt bands - while the 1130 uses the Selectric I ball - 22 positions and four tilt bands.

IBM manufactured the golf balls with injection molding, then coating the plastic with metal in large part because early customer reaction to the uncoated plastic versions were negative. The customers associated plastic with inexpensive (this was the early 1960s) and the price of selectric typewriters and type balls didn't seem justified for plastic parts. The metal made it appear more expensive and durable.

Selectric type element

It would require some fancy design work - the typeball is an overall spherical outline but the individual font characters have to be made with a reverse vertical curve, since the platen where the character will strike is a cylinder. The font is thus raised higher at the top and bottom, least in the middle, to correspond to the platen whose maximum diameter intercepts the middle of a character and the top and bottom are further back from the typeball.

Essentially I would have to design the font characters, turn them into 3D shapes, distort them by the curve of the platen, then orient them to the band of the typeball where that letter sits and place it at the rotational position (rotate) around the ball where it lies around the band (tilt). Once these are in place, the inside is hollowed out, the mating hole is defined for insertion onto the typewriter stem, and holes are drilled for the plastic cap, I can set up the mold to form this object.

The mold would have to be a bit complex in order to be able to release the typeball after molding. The largest diameter of the ball is one of the bands filled with font characters, but separating the upper and lower molds of a plastic part require the part to angle inwards. If it were flat at the separation, when I pulled the mold apart, the raised parts of the letter would snap off. Further, if I put the separation in the midst of a type band, the "join line" that is visible on any molded object would affect the typed characters.

I might eliminate any letters on the middle band that is where the mold would be split - but that leaves me with 72 printable positions on my 96 character Selectric III based system, while the actual 1130 ball had the ability to hold 88 characters. Unless the actual characters on the ball were 72 or less, this would not give me the ability to type everything possible on a real 1130. Further, it would then be incompatible with the restored 1130s that might want to use such a ball - they expect characters at specific tilt and rotate positions that I would have to match. The only upside is a simpler mold.

The solution to his is to make a ring shaped internal submold - called an insert, actually two half-rings, that would wrap around the middle band. This insert would have the mold image of the characters for that band, but its outer face would have the draft (narrowing as it moved deeper into each mold half) to allow the halves to separate. Once the mold is opened, the insert itself is removed leaving the spherical typeball.

This requires a bit more jockeying in Inventor, but should be as achievable as the overall typeball design. Yes, this seems like a tremendous amount of effort, given that I already have a console printer that works with a readily available Selectric III ball. But, there are a few advantages. First, by mapping the characters on the same sides of the ball as on the 1130, I would eliminate the complication and delays of the hidden shifts. Second, I some of the characters on the 1130 are not found on golfballs for typewriters - thus I can't get exactly the same typed output with the current approach. Third, the special characters used with APL are not found on typewriter golfballs and the 1130's typeball is extraordinarily rare.

Inside and outside of a Selectric I style typeball

To support APL on the console I would either need to spend a lot if I was luck enough to find one for sale, or I would need a custom manufactured one. No market exists for custom golfballs and nobody remains in business making them, thus it would need to be self-manufactured.

I am very likely to use injection molding for the typewriter knob and buttons and tab setting lever, less so for the disk drive handle or for various cosmetic touches, and somewhat unlikely to take on the very complex and risky typeball project.

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