Solution: replacement rubber mat for IBM Model M

[Erisie]

My Model M has gone through a series of fixes, part replacements and whatnot. After a bolt mod gone wrong that cracked the barrel frame, some keys on the lower rows (N, M, Down Arrow, Num 0) began to repeat/shatter.

As a permanent hardware fix, I bought a new barrel plate from Unicomp and did the whole process again. However, the keys were still failing in the same spots. It was clear that this hadn't been a barrel frame issue (or at least, not entirely. And the springs, cable, controller board and membrane (the latter three got fresh replacements) couldn't be responsible either. By elimination, the culprit must have been the one part that didn't get replaced: the black rubber mat between the springs and the membrane. During the repair process, I saw some discoloration and wrinkling (liquid damage), but I thought the pressure of the bolts with the metal plate would make that a non-issue. I was mistaken and my keyboard was shattering once again.

The easy solution was ordering a new rubber blanket from Unicomp (part number 1403033), but paying US$20 plus shipping to my country was excessive for such an inexpensive part. I live outside the US and FedEx's rates are obscene in my country. And leaving the rubber mat out wasn't my idea of a fix either.

I had to think of a solution: some sort of rubber mat with the right length, width and thickness. A custom buckling spring project on Deskthority pointed out that the rubber blanket is 8 mil thick: 0.20 mm in metric. After looking on several websites of industrial elastomer suppliers, I stumbled with an interesting alternative:



Rubber resistance bands, like the ones used for physical therapy and Pilates. The red one (Light) that I found on a local health supplies store was 0.2 mm thick, 6 inches wide (15 cm) and 4 feet (1.5 m) long. And it was cheap enough at US$5, so it couldn't hurt to give it a shot.

Unfortunately, I did not take any pictures of the process, but let me tell you that this replacement works. The width is barely enough for a standard Model M, but it does the trick of keeping a barrier between the hammer springs and the Mylar membrane. Make sure to use the membrane to mark the holes and perforate the resistance band with a punch-and-die set, or a leather plier with a popsicle stick underneath.

[andresteare]

Hi! I kinda messed up bolt modding my M122 and I'm thinking of buying a rubber sheet from aliexpress, I would appreciate your help with a couple of questions:

- Would you describe the thickness 0.2mm as just what it's needed? in aliexpress I see options for 0.2mm and 0.3mm

- How about the sound and feeling, did the mat swap restored it?

[Erisie]

Hi! I kinda messed up bolt modding my M122 and I'm thinking of buying a rubber sheet from aliexpress, I would appreciate your help with a couple of questions:

- Would you describe the thickness 0.2mm as just what it's needed? in aliexpress I see options for 0.2mm and 0.3mm

- How about the sound and feeling, did the mat swap restored it?

First of all, apologies for replying all these months late. In case ordering a new blanket from Unicomp is too expensive, I would recommend you ordering this silicone sheet from Aliexpress and cut it to size. The difference between 0.2mm and 0.3mm is so minute and insignificant that I don't think either choice would make much of a difference. I just tried to stay around the range of the original rubber blanket.

The keyboard sounds and feels like a Model M should, but my reason for putting in a replacement is to protect the Mylar membrane from the typing.

[fohat.digs]

the original rubber blanket.

What Unicomp sells now is an extremely thin white latex blanket. I did not measure it, but it is much thinner than the original rubber one, and most people who use it are pleased.