Author Topic: Model F 122-key Terminal Keyboard conversion supplement  (Read 4422 times)

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Offline fohat.digs

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Model F 122-key Terminal Keyboard conversion supplement
« on: Sun, 04 December 2011, 20:10:38 »
You should read these threads before you waste any time on my little subset.

If you are considering doing this conversion in order to get a full-size, Buckling Spring, Capacitive Switch keyboard that will connect to a 21st century motherboard, please make sure that you know what you are getting into. This is not “rocket science” or electrical engineering, or tool & die shop, but it is a project that requires some moderate time, energy, and ingenuity.

I am standing on the shoulders of the real problem-solvers like Soarer and Kishy, who pioneered and perfected this process of taking an early Reagan-era IBM Model F keyboard and bringing it up to date. Please refer to Soarer’s outstanding instructions in “XT/AT/PS2/Terminal to USB Conversion with NKRO” for the electrical juggling involved.

This article is a mere supplement to these earlier works, to help guide you through the drilling and bolting of the physical pieces of these ancient beasts.

Presumably you already have an IBM Model F keyboard, 122-key terminal type to work with. These are nothing like “space-saving” or “lightweight” models. Even IBM Model Ms seem wimpy in comparison to these steampunk behemoths. This is not to say that I like the monstrous size – my ultimate preference would be a straight, full-numpad Model M (with the slightly smaller footprint of some of the newer Unicomp ones) with capacitive switches and the “feel” of the Model F. I have a Model F AT but the layout is too problematic to allow me to enjoy using it. And the Model F XT feels even better, but the layout is even worse, so I do this to re-create the Model M configuration as best I can.

Mine are 6110347 part numbers, and I was lucky enough to find 4 in varying states of disrepair, from which I (barely) created 2 working Frankensteins from the salvaged parts. Needless to say, I ruined multiple components during the course of my quest, so it was crucial that I had spares.

Let me reiterate that this article is strictly the “shop” portion of the project, Soarer provides all electronic knowledge for this undertaking. I am making up names for some of these pieces, if there are “proper” names, please let me know.

My experience tells me that the most fragile and difficult component is the rubber mat (“mat”) that lies between the metal plate (“plate”) and the printed circuit board (“PCB”), which is affixed to another metal plate (but I have never separated these 2). Also, the top shell of the case tends to break in the lower corners.

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If the case is broken, I have had moderately good success using “JB Weld” epoxy (automotive supplies) and embedding a reinforcing bar (a bent piece of wire, mine cut from a paper clip) in a gob of epoxy on the inside. See photos of my ghetto turnbuckle/rubber band technique to hold the sides in place until they cure. JB dries to a perfect dark gray if you are planning to paint the case that color, otherwise it is pretty ugly. I think that they use metal dust as filler.

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My process was to clean and sand the metal plate to remove corrosion, and then paint it with Rustoleum. Since the first one was red, I did this one in green. I masked the plastic clips that hold the stabilizer wires, giving them one very light coat of paint on from the backside at the end.

I fabricated a new rubber mat using a green foam sheet from an art supply store. Rather than use an existing mat for a template, and risk ruining it, I taped the foam to a metal plate (I had an extra plate that was too rough to salvage, you may not be so lucky, but it should be OK) and sprayed paint to mark the mat through the holes. It worked well enough, I had to use some guesswork on the fuzzy ones.

The alignment tabs on the plastic barrels looked like a potential problem, so I used a 5/8” hole punch instead of 1/2”, which is the actual diameter of the barrels, and offset the holes to accommodate the tabs. That seemed to work well enough. The punching was a “piece of cake”, since the punch was made for leather and the foam was far less tough. One good whack with a hammer, with a block of wood below, (it had me scared in the beginning but was actually easy) it took less than 10 minutes.

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Having gotten excellent results from “bolt-modding” IBM Model Ms, I decided to throw in a few bolts here, too. The layout is far different, so you would have trouble placing more than a dozen bolts on this board, rather than the 50 or so on an M. I found that 8 was enough for me.

Having a spare printed circuit board (“PCB”) and metal plate made it a lot easier for me, since I could use the junk parts as drilling templates for each other, etc. With no spares, I recommend drilling the PCB first, then using it to drill the plate. I used a 7/64” bit (please forgive me for not researching the metric equivalents).

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I opted for larger bolts, 4-40 x 1/2” with no washers (tight clearance issues) in the lower side, and 4-40 x 3/4” with washers both sides, including rubber washers, on the upper half.

Eventually, I gave up struggling with the “sliding tab force fit” or whatever they call the original way these beasts were assembled, which is tedious with the original rubber mats (thin), but far worse with a thicker, firmer pad. In exasperation, I got out my tin snips and just cut the damn things off. Now, I depend entirely on my bolts to hold them together and keep them aligned.

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The smaller Fs (XT and AT) do not exhibit this difficulty, since they are so much smaller and you do not have to force the PCB so deep into the curve. I strongly recommend that you keep the tabs on during all the aligning and drilling phases!

Now, it is simply a matter of inserting the barrels and springs and bolting it together. I must admit that I had to put mine together and take it back apart 4 times, for various issues, mostly spring-related (and I am experienced at having taken apart and re-assembled Model Fs of all 3 types (XT, AT, and 122) a minimum of 3 each, some many more, and it is always frustrating). Bolts rather than tabs DO make this job much easier.

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I sprayed the bottom of the case (shell, whatever) with black rubber “paint” and cut a piece of black felt to fit. I edged all the parts that fit together with black electrical “friction” tape, the fabric kind that is not very sticky. I stuffed extra padding into the bottom section to deaden the sound somewhat, but I did not floss the springs, this time.

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This keyboard has a light feel, nice loud ping, metallic and resonating, and compares very favorably with my “stock” model of this same board. For now, I am not going to add more bolts, but you can adjust the feel with more bolts, and/or torqueing them looser or tighter. Perhaps my concept of using rubber washers and torqueing tight is not for you.

I would not worry with fabricating a new rubber pad if I was lucky enough to get a good one, but you should be comforted to know that you can make one for yourself if you have to.

Please feel free to comment, criticize, or add to this article. It is my first serious contribution to Geekhack, and I want to create value and credibility for myself if I can.
We don’t have a conservative movement anymore. We have an infotainment complex aimed at pushing merch to morons.
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Offline Mikelittoris

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  • Location: Sweden
Looking good.
« Reply #1 on: Sat, 10 December 2011, 20:29:11 »
Great work, that keyboard looks really good. This is very inspiring for me since I've got a 122-key terminal board and a Teensy coming to Sweden next week (hopefully). I'm thinking about painting my keyboard aswell, it looks like yours still have the original texture, what kind of paint did you use? :)
IBM Model M SSK -91 (Bolt moded), Geekhack ESC, RGB modifiers and lt blue WASD cluster.
IBM Model M -95
IBM Model N2 -94
IBM Model F -85 (122-key Terminal) Using a Teensy with Soarer\'s adapter code.

Offline fohat.digs

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Model F 122-key Terminal Keyboard conversion supplement
« Reply #2 on: Sat, 10 December 2011, 21:45:15 »
I painted the case with a vinyl paint that I purchased at an automotive supply store. I think it was called "Dupl-i-color" but there will be another manufacturer in your country. It is sold as a touch-up product for interior components such as dashboards and door panels.

"Vinyl Dye" was what I really wanted, but never succeeded in finding it.

This is like a thin paint, but I feel certain that it will scratch or wear eventually. I used several very thin applications, from different angles. I cleaned the case very thoroughly with powdered laundry detergent and a rough sponge.

It does have a subtle, non-glossy texture, but the paint was a film-forming product, rather than a penetrating product.

If you have a Model F, you will probably want to paint the metal plate under the keys, since it will likey be corroded and ugly. A light bright color is very sharp.

If it is a Model M, that layer will be plastic, either beige or black depending on age.

Good luck!
We don’t have a conservative movement anymore. We have an infotainment complex aimed at pushing merch to morons.
— Peter Henlein June 15, 2024

Offline slueth

  • Posts: 577
Model F 122-key Terminal Keyboard conversion supplement
« Reply #3 on: Sat, 10 December 2011, 21:45:46 »
Do you happen to have spare feets and springs?  I would like to buy some from you.  Lost some and I want to put my model f together again.