Replacement Foam Mat for IBM Model F Keyboards?

[Hypersphere]

I would like to replace the foam mat that resides between the metal plates on my IBM Model F keyboards (AT, XT, and 122-key). I have some acid-free foam board in black and in white, but it is 1/8-inch thick. I saw a post on GH that recommended 1/16-inch thick "art foam". However, I am having trouble locating a source of the thinner material.

Has anyone here tried this replacement? If so, which thickness of foam should be used? Could you please indicate the exact name of the product and where it can be purchased? I am in the continental US, so a US supplier would be best for me. Thanks.

[Parak]

The problem is that the curve is quite variable from board to board. Often what will happen is that 1/32 will be sufficient for top and bottom rows, but the middle will need double or triple that. So the ideal material is something that can compress from that thickness down to 1/32 as needed, last a long time or be cheap enough to readily replace, and have enough give to close without the aid of a multi ton press.

I've yet to find something that would work while not requiring bolt mods, but I think I'm very close to a solution...

[vivalarevolución]

fohat.digs on Geekhack has done this and I have done it using his guide. His method seems to work. It seems that you have seen his post.

http://geekhack.org/index.php?topic=487 ... msg1122437

My Model F 122 actually has two switches that do not work consistently, but I think that has something to do with my poor hole cutting skills.

[Elrick]

Please excuse my suggestion here, since I have no experience in fixing a Model-F keyboard, BUT is there a way to use a sheet of silicone instead of the poor quality foam that is constantly required?

Silicone should last for many decades inside any IBM keyboard hence why isn't anyone using it by now?

[Parak]

Please excuse my suggestion here, since I have no experience in fixing a Model-F keyboard, BUT is there a way to use a sheet of silicone instead of the poor quality foam that is constantly required?

Silicone should last for many decades inside any IBM keyboard hence why isn't anyone using it by now?

You mean like this?

[Muirium]

One just like that in Kishsaver format, please!

[rindorbrot]

Make that two, please
I could use one too.

[vivalarevolución]

Where did you get that silicone material? I might give that a try on my next Model F refurb.

[Game Theory]

Though in the states I got my silicone sheet for my F AT from http://www.grainger.com/
an industrial supply company. Amazon also has some too. Be careful to pick the durometer you want.

I used leather punches to make the barrel holes and I made the notch with a smaller punch. I marked the area to punch with spray paint. I had to repaint the plate since it was fairly rusted. Used too much paint in the end. Got rid of the rust with vinegar.

IMG_20131117_193434-2.jpg (510.01 KiB) Viewed 20920 times

[Hypersphere]

Though in the states I got my silicone sheet for my F AT from http://www.grainger.com/
an industrial supply company. Amazon also has some too. Be careful to pick the durometer you want.

<snip>
Thanks for the tip. It seems that people are recommending a silicone rubber sheet rather than "art foam" or "coreboard" or other similar styrofoam products. Grainger has a very comprehensive catalog. Which specific product and thickness did you use? Thanks again.

Edit: I notice you also cautioned us to choose the desired durometer or indentation hardness. What durometer value do you recommend for a model F keyboard foam layer replacement? Thanks once more!

[Hypersphere]

Further to this, what is the purpose of the foam layer? What happens if this is omitted when you reassemble the keyboard?

[Hypersphere]

The problem is that the curve is quite variable from board to board. Often what will happen is that 1/32 will be sufficient for top and bottom rows, but the middle will need double or triple that. So the ideal material is something that can compress from that thickness down to 1/32 as needed, last a long time or be cheap enough to readily replace, and have enough give to close without the aid of a multi ton press.

I've yet to find something that would work while not requiring bolt mods, but I think I'm very close to a solution...

I just took a look at the foam layer in an XT. The thickness appears to be about 1/8 inch throughout. However, there is a small border around the edges where the two metal plates come together that looks like highly compressed foam that is nearly paper-thin. This thin material protrudes from the metal plates along the top and bottom edges.

[Parak]

Further to this, what is the purpose of the foam layer? What happens if this is omitted when you reassemble the keyboard?

The bend of the top and/or bottom plates is not uniform in respect to the other, and not sufficiently precise to exactly fit barrel+pcb+mylar, which means the barrels will have a lot of wobble without some foam layer in pretty much every axis. Especially the Z axis impacts the feel and the sound, and allows for flippies to potentially slide out of their grooves. Basically, all sorts of bad, similar to what happens with Ms when they lose their rivets. The foam allows for a variable height firmness layer to press into the barrels from the top plate, making sure that they have no play regardless of where in the plate they might sit.

[Parak]

I just took a look at the foam layer in an XT. The thickness appears to be about 1/8 inch throughout. However, there is a small border around the edges where the two metal plates come together that looks like highly compressed foam that is nearly paper-thin. This thin material protrudes from the metal plates along the top and bottom edges.

The parts that you want to measure are is the fully compressed layer of foam in each row, especially middle vs top and bottom rows, subtracting the thickness of the plate itself. Usually best done with a micrometer.

[Hypersphere]

Further to this, what is the purpose of the foam layer? What happens if this is omitted when you reassemble the keyboard?

The bend of the top and/or bottom plates is not uniform in respect to the other, and not sufficiently precise to exactly fit barrel+pcb+mylar, which means the barrels will have a lot of wobble without some foam layer in pretty much every axis. Especially the Z axis impacts the feel and the sound, and allows for flippies to potentially slide out of their grooves. Basically, all sorts of bad, similar to what happens with Ms when they lose their rivets. The foam allows for a variable height firmness layer to press into the barrels from the top plate, making sure that they have no play regardless of where in the plate they might sit.

This makes me wonder about alternative approaches that might have been used in the construction of these keyboards, such as threaded barrels held in place with nuts and lock washers. With rubber washers on the other side of the plate, one could tune the keyboard using a torque wrench. I suppose this design would have been more expensive and labor intensive to build.

[Parak]

So, what I ended up doing at least for now, is using 1/32" ~50 durometer silicone. I cut the overall sheet as per above, and punched the holes, etc. Then, after closing and opening a few times, I determined that row 4 needs one more layer, and row 2 and 3 two more layers. The best way of doing that is to cut and punch an additional three row wide mat, then a two row one, but I'm too lazy at this point and simply cut thin strips (the width of the non-stem barrel portion), and overlaid them on top of each other and the overall mat. Worked well enough, and all barrels have none or negligible play once closed.

On closing and opening: it will definitely be harder, but I've learned another neat trick. First I clamped it, then wedged something with leverage, like a handle of a wrench, into the gap where the bottom plate goes from concave to straight (where the bolt holes are for case mounting). Then simply gently push towards the top plate to get it sliding open or closed, depending on which end you're using, alternating a little lengthwise. Pad against the top plate as needed if you've painted it. Be careful not to push /down/ into the top plate, but against the side only.

Of course the best way to close still is to use something like a pipe clamp or two, but opening is great using the method above.

[Hypersphere]

Interesting. Perhaps the reason foam is used is that it is highly compressible, thus adapting to the need for variable thickness from one row to the next.

[quantalume]

I'm too lazy at this point and simply cut thin strips (the width of the non-stem barrel portion), and overlaid them on top of each other and the overall mat. Worked well enough, and all barrels have none or negligible play once closed.

This is an interesting idea. Silicone sheet is expensive, so the less you use the better. They also make adhesive-backed sheets. Perhaps one could do an entire keyboard this way, i.e., affix long, narrow, adhesive-backed strips between each line of barrel holes on the inside of the top plate.

Are you happy with the 50A durometer? I was thinking something in the range of 20-40A would be better.

[Hypersphere]

Would it be feasible to use silicone or foam washers or pads on each barrel instead of a silicone or foam mat that covers the entire plate?

[Game Theory]

I think I use the 30A (or 40A). I bought both sheets at the time but cannot remember which I used.
Scale http://www.smooth-on.com/Durometer-Shor ... index.html


Don't know about the washers. How would you handle the notch? Just uses bigger ones?

[vivalarevolución]

Wcass linked to this foam as a possible replacement:

http://www.mcmaster.com/#8647k102/=s16obu

[Hypersphere]

Wcass linked to this foam as a possible replacement:

http://www.mcmaster.com/#8647k102/=s16obu

This foam looks like it might be a good approximation of the original material.

The following post on GH used "art foam":
http://geekhack.org/index.php?topic=37753.0

I have found a similar material called Sintra PVC board that comes in various thicknesses, including 1, 2, and 3 mm, and in sizes large enough for IBM Model F AT, XT, and 122-key keyboards:

http://www.foamboardsource.com/sintra-p ... board.html

[Hypersphere]

I think I use the 30A (or 40A). I bought both sheets at the time but cannot remember which I used.
Scale http://www.smooth-on.com/Durometer-Shor ... index.html


Don't know about the washers. How would you handle the notch? Just uses bigger ones?

I suppose it would be possible to use a punch to make a hole in a washer or pad to accommodate the barrel peg.

[vivalarevolución]

I linked that art foam thread earlier in the thread. I have it in my refurbished Model F 122, but I am not crazy about it. I wonder if that fire and weather retardant foam has a longer life. Probably, because art foam is not going to be weather retardant.

[Hypersphere]

So, what I ended up doing at least for now, is using 1/32" ~50 durometer silicone. I cut the overall sheet as per above, and punched the holes, etc. Then, after closing and opening a few times, I determined that row 4 needs one more layer, and row 2 and 3 two more layers. The best way of doing that is to cut and punch an additional three row wide mat, then a two row one, but I'm too lazy at this point and simply cut thin strips (the width of the non-stem barrel portion), and overlaid them on top of each other and the overall mat. Worked well enough, and all barrels have none or negligible play once closed.
<snip>

There are several industries that produce silicone, silicone foam, and silicone sponge materials for various applications, including electronics. One example is Stockwell Elastomerics:
http://www.stockwell.com/
After looking at some of the information on their site, I am persuaded that silicone sponge sheets could be an ideal material for an IBM Model F foam mat replacement. The sponge is available with sufficient compressibility that it should be possible to use a single layer to hold all rows of barrels in place.

[quantalume]

I've been eyeing this stuff: http://amzn.com/B004JU1VFK. One could adhere a strip beneath each row of holes, possibly two strips on top of each other near the center of the keyboard where the gap is sometimes wider. All you need is something to hold the barrel assemblies in contact with the PCB, without providing so much resistance that it becomes difficult to reassemble.

[wcass]

How i make replacement foam ...

print out my template at 100% on paper big enough to fit it (just a few cents at the office supply store).
check measurements are accurate. if too small/big, adjust scale and re-print.
stick thin double-sided tape on the back - just outside the boarder.
unroll new foam material on top so that it sticks to the tape.
use dies/mallet to punch out the holes.
use a razor to cut the slots.
use scissors to cut the boarder.

For foam material i use 1/16" neoprene. It compresses easily to .5mm and is cheap.
http://www.mcmaster.com/#8647k102/=s0yd5e

I got my die set from HF. They go on sale from time-to-time.
http://www.harborfreight.com/9-piece-ho ... -3838.html

Some folks punch a single big hole that goes around the notch. I prefer to make two punches. Ether way will work. My template for the Kishsaver is below. TBH, i have not used this specific template myself (my foam was in like-new condition) so double check the positions. I have templates for the AT and 122 also; PM me if you need one.

Pad.pdf

(36.04 KiB) Downloaded 554 times

[Muirium]

Now that's a how to! Thanks for the details, Wcass. I'll check this out when I work on an F that needs new foam. To my relief, my Kishsaver's is actually in fine shape, the only crumbling was on the exposed outside edges.

[vivalarevolución]

Wcass, have you experimented with different types of foam you can order from McMaster and found out the one you linked is the best for this application? I noticed that they have lots of options.

[wcass]

Wcass, have you experimented with different types of foam you can order from McMaster and found out the one you linked is the best for this application? I noticed that they have lots of options.

I have very little experience actually. I knew that i needed something thick enough to fill the wider spots but it needs to compress down for the tight spots. I filtered for "extra soft" or "soft" and that left me with just two options (excluding buying full rolls) - the stuff i linked to and silicone foam. The silicone was 10x as expensive, so I just went with neoprene.