Yet another beamspring refurb (5251)

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09 Mar 2019, 20:00

Rattling in the sense, that the switches don't sit tight and can be wiggled around: Yes, that is fixed now.
If you mean rattling in terms of sound: Sound was pretty much unchanged by the restauration.


10 Mar 2019, 01:32

Beamspring switches have the most play of any switches. You can rotate keytops like 5 degrees when they sit. You can press a 7U beamspring spacebar about 90% of its length with no stabilizer bar.


15 Mar 2019, 23:15

SneakyRobb wrote:
27 Feb 2019, 21:22
So I am now in the not sure what the keycaps are made of camp. I am waiting to hear back from the IBM archives guy. IBM developed acrylic injected keycaps in 1967 but I am fairly certain they are the clear relegendable ones on displaywriters, model f/ and pingmasters.

I tried the acetone on one black with white legend beamspring key and it sort of did something to the black outerplastic. No colour came off though onto the cloth. I could easily scrape off the slight discoloration and make it shiny again though on the black part so I don't know if it just has a laquer on it and the acetone did something to that laquer.

On the white plastic doubleshot inside of the same key, the acetone did nothing.

So the blackpart could be ABS although I have found no references to ABS being used in any manuals. It does say to never clean beamspring keycaps with alcohol of methyl chloride. This doesn't help much as we are not trying to tell the difference between pbt and abs. Most solvents will melt many candidates pretty equally. Also pbt wasnt really used until the 1970s.

The candidates I have been searching for are abs, acrylic, bakelite, polyimide, melamine, and other formaldehyde plastics. They could also be some variant of polycarbonate.

As for the PEI logo, I believe it is some kind of internal mold marking possibly a subdivision of ibm another company or an outdated material code. Most of the keys have mold marks like M-15 which is probably the specific mold to trace issues. The PEI mark doesn't look like those at all. From what I can tell Polyetherimide wasn't invented until the early 80s.

IBM did update their two-shot injection molding process in the early 80s for replacement keycaps, but it seems more likely they would have just used ABS. As well for some reason they decided to shoot the outer part of the key first then the insert. Perhaps there was some plastic bonding reason for this. Or maybe just nicer legends.

I do know that earlier IBM electric type writers had cellulose and bakelite keycaps that had laquer finishes. So I will wait for the archives guy to see if he has anything.
So the IBM archives guy Max got back to me and the IBM Archives can't find any reference to what type of plastic was used in the beamspring keys.

I may contact the original factory workers.

Through my own research I am now confident enough to say I don't know what they are. (Science!)

From what I have learned they are most likely one of several things. It is likely a thermoplastic. The list is too much, but basically short of me sending a key away for testing, which I am doing. It is likely ABS, Polycarbonate, POM, Melamine, Nylon, PVC, or other thermoset. Narrows it down right?

"Hi Robb,

I've searched the collection and found no indication of the specific plastic IBM used for the manufacturing of the key caps. I looked in the field engineering manuals, maintenance manuals, as well as the IBM Lexington News from that time frame but I did not see anything about the key caps. The same goes for the color. It most of the PR for these typewriters and computers, IBM uses standard language such as "gray" or "red." I think it is safe to assume that they used a specific type of gray or a specific type of red, it is just not mentioned what type.

As you know, it is possible that this info will turn up somewhere, so I will keep an eye out and let you know if I find anything!


Reference Desk
IBM Corporate Archives
2455 South Rd
Bldg 04-02 Room CSC12
Poughkeepsie, NY 12601


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17 Mar 2019, 08:21

Many thanks for the check - wonderful

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