Rubber Membrane Question [Answered]

[Tenkeyless]

Recently I foolishly purchased an IBM Model M 71G4644 from ebay. I did not realize that this was not a buckling spring keyboard, but rather a rubber dome keyboard. Being upset, I decided to take it apart and realized that I could replace the domes with a pivot plate and spring because the plastic cover has the housing for where the plate should go. The entire purpose of this keyboard is to make a Space Saver Model M, but because I'm bored and have nothing to do with my summer I figure this might be kind of neat to tack on to the process of making the Tenkeyless Model M.

Now, for my question. There is a rubber membrane that, for this keyboard model(71G4644), is used instead of the plate and springs. From what I understand, based on the repairing that this guy has done:
http://sandy55.fc2web.com/keyboard/repair_model_m.html

It would seem there is a similar rubber membrane for buckling spring models, but without the domes that you can see in the photo I took. Can I cut those domes off and use the same rubber membrane or should I replace it all together? Also, should I replace it, where could I find one?




***************** EDIT(As well as the suspected answer to my question.) *********************
Sorry it took the entire weekend and into Monday to get back to this. Welp.. good news and bad news. The good news is that the keyboard technically works and there is no squishy or dead keys as far as I could tell. The bad news is that in order to get a response sometimes I am required to hold the key down for a long time.

I suspect at least two things that could be potentially happening. It could either be that the bolt modification that I performed is not up to spec and causing the membrane to be off center and thus requiring me to apply excessive force to the keys. Or, it is the rubber sheet/blanket that prevents proper connection between the switch leads. In all honesty, I'm leaning more towards the rubber sheet/blanket because I feel fairly confident in my work even if it was a noob-time first attempt.

So, suspected answer to my original question:

Can I cut those domes off and use the same rubber membrane or should I replace it all together?

I do not think cutting the domes off and recycling the rubber sheet/blanket will work and I think the best course of action would probably be to replace it all together, however I am still in limbo on where to attain one. Any suggestions?

Also, if anyone was interested, here is the entire gallery of what I was doing from start to finish. Maybe in my documentation someone might see an error that could be corrected. http://imgur.com/a/HiFRj

Probably sometime today or tomorrow I will try tightening the bolts and/or removing the rubber sheet/blanket to see if that may potentially solve the problem.




***************** EDIT#2(Final result and conclusion.) *********************
I am now typing to you from my modified keyboard. Here's the image of the finished product:


Here's some further information on the rubber blanket that this entire thread is supposed to be about. I talked with Unicomp and apparently the rubber sheet in question is called a blanket. Also, a new one can be ordered through the Membrane Assembly by entering into the part number field with: "Blanket part number 1403033"

This is the blanket part number for a Buckling Spring Model M. Commenting on the blanket, this blanket is incredibly thin. It feels similar to that of a rubber glove. So to finally answer everything.

Can I reuse the rubber dome membrane?
 -> No, it's too thick.
Where can I get a replacement rubber sheet?
 -> Unicomp website under the Membrane Assembly using  "Blanket part number 1403033" in the product field.

And I think that covers it. Thanks everyone for your advice and help. I hope you enjoyed the little documented experiment.

[The_Ed]

It would be far easier, and most likely cheaper, to just buy a proper Model M...

[Tenkeyless]

You're probably right, but this sort of gives me an opportunity to experiment with modifications that I originally planned to do anyways. If were to cut off the domes so that the pivot plates would lay correctly do you think there would be an issue of there being a dome hole? Or what about taking out the rubber completely?

[The_Ed]

I don't think you can use that membrane as they actuate differently. (Though old IBM rubber dome membranes may be different)



So you would need to order a new proper membrane, a rubber sheet, the pivot plate and spring assemblies, and the nuts/bolts/tap for a bolt-mod AT MINIMUM.

AND you wouldn't know if the new membrane would have the same matrix as the rubber dome one, so it could thus be incompatible. In which case you'd need to teensy it too...

Go buy a proper Model M...

[Tenkeyless]

Here is a photo of the disassembled keyboard at my desk.


Going into my original project, I knew I would have to bolt modify the keyboard. As for the plates and springs, I can easily purchase those from the Unicomp website. I think they sell them for $0.20 or something like that. The membrane shouldn't act all that differently whether its done by rubber dome compression or the plate compression. Of the three sheets comprising of the membrane, the two outward sheets need to be forced to connect with each other and as far as getting this done I am not sure whether the process is different between the two actions. However, I think that the rubber sheet acts a sort of shield that protects the membrane from being worn down by the plate. My guess is that if I cut the dome out the rubber sheet, the plate would still compress the two sheets together to make connection, but I'm uncertain if the dome hole in the rubber sheet would effect connection. The force from the plate would act on the rubber, but the force from the rubber would not necessarily act uniformly on the membrane. Would that matter though? Maybe the two sheets only need to connect slightly.. hmm.. pondering.

[fohat.digs]

I sent you a PM.

I think that the rubber dome membrane is far thicker than the rubber mat in the mechanical Ms. My guess it that it would prevent the plates from coming together enough, but if you are bolt-modding you might be able to force a squeeze.

[Tenkeyless]

I sent you a PM.

I think that the rubber dome membrane is far thicker than the rubber mat in the mechanical Ms. My guess it that it would prevent the plates from coming together enough, but if you are bolt-modding you might be able to force a squeeze.

Hmm.. if it is thicker rubber material(assuming that dome holes won't effect the performance of the plates) and I can't get it to squeeze, I may actually PM you later on about your offer.

[wcass]

this should work without the rubber domes altogether; i wouldn't bother trying to reuse it. it is true that a BS model M uses a thin rubber sheet between the pivot plates and membrane, but i have heard from other M enthusiasts that it works fine without it.

if you are ordering pivot plates and springs from Unicomp, you might ask for a rubber mat too.

[The_Ed]

Does the membrane have 3 layers, with the rubber domes being the fourth layer? If so this may work if you buy a rubber sheet of the right thickness to put on top of the membrane. Cutting out the domes simply will not work reliably, and most likely not at all. And the pivot plates would then destroy the membrane over time as there would be no rubber in-between because of the missing domes.

Another thing on your list of needs would be BS compatible keycaps.

[Tenkeyless]

this should work without the rubber domes altogether; i wouldn't bother trying to reuse it. it is true that a BS model M uses a thin rubber sheet between the pivot plates and membrane, but i have heard from other M enthusiasts that it works fine without it.

if you are ordering pivot plates and springs from Unicomp, you might ask for a rubber mat too.

Thanks. I am going to still attempt to reuse the rubber sheet that I have just to see if it's possible. Otherwise, I may just go without the rubber altogether, but I will report back on the success or failure of the reused rubber sheet.

[fohat.digs]

this should work without the rubber domes altogether; i wouldn't bother trying to reuse it. it is true that a BS model M uses a thin rubber sheet between the pivot plates and membrane, but i have heard from other M enthusiasts that it works fine without it.

if you are ordering pivot plates and springs from Unicomp, you might ask for a rubber mat too.

The rubber mat must serve some purpose, I figured that it is a cushion to keep everything smooth. It must soften the sound, at least a little bit.

Over time, it seems like the mylar sheets would abrade themselves against bare metal.

I have heard these "rumors" but I can't recall ever seeing a realistic report or review of it.

Have any of you actually done this?

PS - I think that Unicomp's terminology for this item is "blanket"

[Tenkeyless]

So I figured I would update my progress if anyone was curious. So far I've managed to drill all the proper holes and I'm getting ready to bolt everything down after I cut off the number pad area. I plan to get to all the cutting and stuff tonight if I have some time, but I figured I would show you the holes that I started drilling and the holes I'm cutting out of this rubber blanket or sheet. I'm hoping it will work. Once everything is finished I'll let everyone know. Here's some pictures so far. I have a video, but I dunno if anyone is interested.

Here's the gallery:
http://imgur.com/a/emgBh#0

Some of the photos aren't the best quality, but it sort of shows the general idea. At any rate, I should be able to finish my tenkeyless model m by this weekend. So hopefully I can post photos later and update you about the rubber sheet/blanket/pineapple.

[fohat.digs]

Those are some mammoth holes. I use a 1/16" bit and 2mm bolts.

[Tenkeyless]

Those are some mammoth holes. I use a 1/16" bit and 2mm bolts.

Yeah, the bolts I'm using are 2mm x 8mm. The underside looks worse than the other side. I used a micrometer on my drill bit and it came to 2.23mm. I can't really explain why it looks so silly, but for my first bolt mod job I'm fairly pleased.

[Tenkeyless]

Sorry it took the entire weekend and into Monday to get back to this. Welp.. good news and bad news. The good news is that the keyboard technically works and there is no squishy or dead keys as far as I could tell. The bad news is that in order to get a response sometimes I am required to hold the key down for a long time.

I suspect at least two things that could be potentially happening. It could either be that the bolt modification that I performed is not up to spec and causing the membrane to be off center and thus requiring me to apply excessive force to the keys. Or, it is the rubber sheet/blanket that prevents proper connection between the switch leads. In all honesty, I'm leaning more towards the rubber sheet/blanket because I feel fairly confident in my work even if it was a noob-time first attempt.

So, suspected answer to my original question:

Can I cut those domes off and use the same rubber membrane or should I replace it all together?

I do not think cutting the domes off and recycling the rubber sheet/blanket will work and I think the best course of action would probably be to replace it all together, however I am still in limbo on where to attain one. Any suggestions?

Also, if anyone was interested, here is the entire gallery of what I was doing from start to finish. Maybe in my documentation someone might see an error that could be corrected. http://imgur.com/a/HiFRj

Probably sometime today or tomorrow I will try tightening the bolts and/or removing the rubber sheet/blanket to see if that may potentially solve the problem.

[fohat.digs]

I feel sure that it is the thickness that is killing you. The standard blanket on an old M is a fraction of a millimeter thick, and I understand that the new Unicomp ones are even thinner. I would guess that the rubber dome sheet is a full mm thick, if not more.

The no-cost solution is to cut one yourself out of paper or plastic.

PM me if you want the Model M carcass I told you about. It will cost a little more to ship, but you will have all the pieces for spares, or for another go at any part of it, such as the case.

[Tenkeyless]

I feel sure that it is the thickness that is killing you. The standard blanket on an old M is a fraction of a millimeter thick, and I understand that the new Unicomp ones are even thinner. I would guess that the rubber dome sheet is a full mm thick, if not more

You are absolutely correct. I am now typing to you from my modified keyboard. Here's the image of the finished product:


Here's some further information on the rubber blanket that this entire thread is supposed to be about. I talked with Unicomp and apparently the rubber sheet in question is called a blanket. Also, a new one can be ordered through the Membrane Assembly by entering into the part number field with: "Blanket part number 1403033"

This is the blanket part number for a Buckling Spring Model M. Commenting on the blanket, this blanket is incredibly thin. It feels similar to that of a rubber glove. So to finally answer everything.

Can I reuse the rubber dome membrane?
 -> No, it's too thick.
Where can I get a replacement rubber sheet?
 -> Unicomp website under the Membrane Assembly using  "Blanket part number 1403033" in the product field.

And I think that covers it. Thanks everyone for your advice and help. I hope you enjoyed the little documented experiment.