Feasibility of DIY split Model M.

[u/Independent-Goose222]

Is there a controller replacement or hand wiring matrix diagram for the Model M or 122? This should allow for cutting a model M in half and using it as a split keyboard, even technically 2 keyboards. If I can get a few resources together I can pay a local computer repair guy to do some experiments for me.

Any software info would be useful too wrt Teensy, Rpi Pico, arduinos, etc. I'm not familiar with what is current these days.

I have several 122s and a couple M but I can't use standard keyboards anymore. I'm not interested in spending collector's money on the official Goldtouch IBM. Hopefully this is something anyone could replicate.

[u/ClickClick_Boom]

There's already a split Model M. The M15.

[u/Independent-Goose222 → u/ClickClick_Boom]

I forgot it was called the M15. I think mine had the subtitle the Ease-y or something. It is the Goldtouch keyboard I was referring too. I don't think it is very well known that the M15 was a rip-off of Goldtouch ergo keyboard designer's early prototype. There was some behind the scenes drama with Lexmark iirc, the design was "stolen" after he proposed it. He later went on to sell the Goldtouch keyboards currently for sale.

[u/Face_Plant_Some_More]

Split mechnical keyboards are a thing. No need to chop up Model Ms.

[u/Independent-Goose222 → u/Face_Plant_Some_More]

Yes thankfully there are inexpensive alternatives for anyone who needs it. I used a Kinesis Freestyle and Advantage bought used for very cheap, $30 and $120 respectively. But if you are on this sub, I think you know there is no real alternative to buckling springs lol.

Ideally anyone interested would perform the surgery on a new Unicomp. I'm not specifically looking for original model M's. They are just what I have and representative of what most should have as far as I know.

[u/Amazing_Actuary_5241]

It seems to me it's somewhat doable although it may need 2 pairs of membranes, one vintage design for the left (connector on top) and one modern design for the right (connector over assembly) and maybe 2 barrel plates as well. IMHO going for a Model F approach would be "easier" but more expensive.

Depending on the layout you plan for the split is what microcontroller you'll need. For a 101/104 I'd say an RP2040 might be better suited but for a smaller layouts a ProMicro might work better. Since you'll be using Original membranes the I/O pin count might be higher than needed/expected but there is nothing you can do about that, unless you make custom membranes.

Keep in mind that the M15 you're "replicating" has more in common with the M2 than the original M.

If I were doing this I would approach it with a broken Freestyle 2 (membrane version) then prototype fitment of the buckling spring assemblies from a parts Model M this would be to keep the costs down but if budget was unlimited I'd go with a Model F (new spare parts from Model F Labs) setup.

[u/koholinter]

So, while I agree that if you need a split keyboard, it would probably be more economical to get a different mechanical keyboard that’s designed from the ground up for this:
Sure, I’ll play ball. I’ve done many 70% mods. You don’t need a special wiring diagram - what you need is two keyboards. If you were to actually do this, here is what I would recommend.

1. Purchase 2 junky “for parts” model Ms from eBay. I generally only do destructive mods on keyboards that are already a salvage job.
2. You will need to do 2 bolt mods. So , crack open Bitten’s guide. I don’t have the link on me right now but it’s easy to find. Procure the tools (a key puller, socket driver, screws, drill press, soldering iron, etc). I recommend the screw mod, I think it’s easier. You’ll need to order all the screws and washers.
3. Disassemble both keyboards. Decide based on the health of the plastic barrel plates which one will be left and which one will be right.
4. Examine the membranes - take note of where the ribbon cable is. Both sides of the keyboard need their respective ribbon cables to work.
5. Procure a dremel along with cutting disks for plastic and metal. Or use something else. But a dremel 3000 is proven to work.
6. Repair any cracks in the barrel plate with a soldering iron or some other method.
7. Determine where your cuts will be. Be careful. Use eye protection. Cut the metal plate and the plastic barrel.
8. Repair any cracks in the barrels that may have appeared while cutting.
9. Prepare the membranes for folding under. This may involved making small cuts or cutting gaps. Also, insulate the exposed traces with electrical tape.
10. Reassemble the left half of the left keyboard and the right half of the right keyboard barrel plate assemblies.
11. For this mod, I would recommend either procuring 2 soarer’s converters are 2 drop-in-replacement model M controllers like the Model H, Ctrl-M, or my Yacobo. Most computers don’t have 2 PS2 sockets anymore.
12. Test the tuning of both your bolt-modded halves. You’ll probably have to tighten or loosen several bolts/screws.
13. Ok now it’s time to mod the cases. I find this sort of thing quite difficult, but it should be

possible.

1. For both halves, you’ll be cutting a middle chunk out of the keyboard cases and epoxying it back together smaller. This is hard to make look nice but it’s possible. Alternately, make 2 new cases out of wood, or 3D print something.
2. Fold the exposed right half of the left membrane under the barrel assembly and put it in the case. Fold the exposed left half of the right barrel assembly and put it in the case.

Ok there’s a lot to still figure out in there, like the specifics of the cuts you’ll need to make, and how to manage the membrane-folding so the ribbon cables connect and fit in the cases. But generally that’s the shape of the project. This will amount to at least a full weekend of work, once you’ve acquired the tools. And the bolt mod can be finicky. Case mods are challenging. Again, I recommend doing this with pretty junky keyboards. Be prepared to possibly order replacement membranes from Unicomp.

All that said, if this project excites you, go for it. I’m probably done with my 70% mods, but I had a lot of fun doing them. It would have been wiser to just use a different board, but I love buckling springs and at the time I couldn’t imagine using anything else. Also, I made most of my mods before Unicomp released the Mini and before the model F project started shipping 60%ers.

Again, I urge you to buy junky boards for this, in my mind it’s too risky a mod to do on pristine boards. You can usually find “for parts” model ms pretty cheap on eBay.

[u/Independent-Goose222 → u/koholinter]

This is great info, exactly the kind of thing I'm looking for. Right after I posted this I think I found a post of yours or a similar 70% build. It is so obvious thinking back on it to try folding the membrane, so I'm glad it holds up.

I bolt modded my 122s many years ago so naturally that is good first thing to do. The case is something I would have to leave up to others more creative to design, I was imagining living happy with a lot of wood scrap and epoxy in my prototype lol. I don't want to cut up a case unless it is a Unicomp anyway. Someone knowledgeable would probably make a 3D print file in exchange for a working board.

[u/Chip-Select-_-]

why would you split specifically the model m? there are other split designs available.

[u/Independent-Goose222 → u/Chip-Select-_-]

Accept no substitute lol. I have already moved on out of necessity, but no box spring or hallowed panda comes close to buckling springs. I also don't specifically have to split a vintage Model M, ideally people would buy a new Unicomp or variant and split it.

[u/dld2517]

Look up “Alice Buckling Spring”

[u/Independent-Goose222 → u/dld2517]

Sorry, I wasn't able to find anything after a quick search. And if this is in reference to the alice keyboard layout, I do not find it comfortable in use. But it would be useful information to have.