[IC] sorbothane (ULTRA-soft polyurethane) landing pads!

[mkawa]

Folks,

Ever since Ray suggested this in the dampening mat thread: http://geekhack.org/index.php?topic=53792.msg1218289#new

I've been talking with a sorbothane app engineer about the possibility of making small landing pads out of 30 OO sorbothane.

1) what is sorbothane?

sorbothane is a an extremely soft, almost gel-like polymer elastomer

http://en.wikipedia.org/wiki/Sorbothane

it is unusual in that it is extremely soft, but has _excellent_ material memory, which means that although it deforms significantly when compressed, it nearly always returns to its original shape as long as the compressive load was not absolutely gigantic.

2) how would it be different from silicone rubber or natural rubber as a landing pad?

well, for one, it is very difficult to make a rubber that isn't actually a messy liquid gel at shore durometers down to 30 OO. here's a quick reference of what shore durometer means, as a rule of thumb:



notice that 30 OO is very close to ye olde gummy bear. yes, a sorbothane landing pad is a lot like putting a very thin gummy bear in your keycaps (but less delicious, i will admit).

3) how much will this cost?

i am currently working on shape, cost and other logistics. however, i am convinced that this item can be made, and it actually feels quite comfortable once you get the geometry, thickness and hardness right. i have samples i have been playing with and what is interesting is that, given the right geometry, you barely lose any key travel. the sorbothane deforms on a hard keypress until it is of negligible thickness and then it pops right back when you release the key.

4) what are the advantages?

it's really the same as any other landing pad, but softer. the idea is that instead of hitting a steel plate and pcb assembly when you bottom your keys out, you hit a very very soft gummy bear that acts almost like a helper spring; this "bottom out helper spring" makes your landing soft, but more importantly, it will react to continued pressing by pushing back very lightly instead of immediately squishing to minimum thickness like silicone or natural rubber.

5) great! i'm sold! let's make these!

unfortunately, there is a problem. the smallest standard size part that sorbothane, the only manufacturer of this material, makes is a 0.5x0.5x0.1" square. i've taken some of these, poked holes in the middle and at this size they are _far_ too large for landing pads. i have been talking to them about tooling up a new tiny mold (won't work), cutting via waterjet (too expensive), and various other things. at the moment, the manufacturing technique they feel is most likely to work is die-cutting large thin sheets. however, we very rarely have items die-cut on GH, and short of moz's die-cutters in india, we don't really have any access with good, inexpensive die-cutting.

6) how can i help?

if you know someone with a very small inexpensive waterjet setup or a die cutting press that will churn out landing-pad sized shapes (from my experiments i'm thinking somewhere around a 0.35" square with a simple pin-hole in the middle. this would work well with the 0.1" material i have samples of. 1mm thin material could be a more traditional 0.4 or 0.45" square, or even a more standard 5/8" OD 3/32" ID o-ring).

that said, i have no idea how popular o-rings and landing pads are these days. i suspect these would be killer with clears or high spring rate blacks, and the thinner material would be perfect for very low spring rate linear switches, like red with 40g-ish springs.

i suspect that they would also feel pretty darn good on topre boards, since the low spring rates on topre switches make bottoming out much more likely.

[riotonthebay]

I'm intrigued.

[SpAmRaY]

Yes please!

[FrostyToast]

Will these feel more mushy or mushier compared to rubber o-rings?

[CK Briefs]

I'm so down! How would this compare to memory foam though?

[mkawa]

memory foam and sorbothane are in the same family of visco-elastic polyurethanes. the major difference is that sorbothane has been formulated use this property to absorb energy and memory foam is constantly being reformulated to get rid of it as quickly as possible (mattress so warm yerrrgh)

as such, sorbothane is about an order of magnitude denser than memory foam. a memory foam o-ring would be largely air (so much so that i suspect it's very difficult if not impossible to cut most memory foam formulations into shapes that small).

[CK Briefs]

So basically, it's not super duper firm, yet it absorbs a lot more energy (in this case, from bottoming out)?
I've never used landing pads or o-rings, so I haven't had a chance to experience softer bottoming out.

[keymaster]

I'm very interested. O-rings are fine but they drastically alter the bottom-out feel. Would these sorbothane landing pads have less of an impact in terms of feel?

[mkawa]

what do you mean by feel?

you can think of a sorbothane pad as a spring with a reasonably high spring rate. that's what i meant by helper spring. so, let's say you have a 40g/mm coil spring in your switch and a landing pad that's 2.5mm thick at rest. key travel is 4mm. for the first 1.5mm, the force needed to push the key down is a constant 40g. at 2.5mm from bottom, the spring rate will initially jump to about 100g (this is very back of the envelope from numbers i threw around with the app engineer), and for the next 1.5mm of travel, the rate will climb from 100g/mm to about 500g/mm until it asymptotically approaches infinity. that's the major difference between sorbothane and silicone rubber or rubber landing pads. they tend to deform very little (the deformation is what's causing the effective spring rate to change), and hence don't have this progressive feel at bottom-out.

now, 2.5mm is the thickest we might go. i have played around with the 2.5mm material and it's ok if you seriously slam your keys down. it will progressively stop your finger without a jarring sort of feel (this is what my understanding of o-rings and landing pads are supposed to do). the other possibility is 1mm thick material, which has the same hardness properties, but is much thinner, so the spring rate will climb that much faster (from 100g to 500g in 1mm instead of 2, but the tradeoff is that you get more space in whcih the very soft coil spring is the only resistance).

interestingly, non-progressive helper springs are often used to soften bump-stop hits (basically the same as bottoming out, but in a car suspension. most of the time, the large spring dominates, but when the large spring on your strut or damper is completely compressed, the helper spring takes over with a higher spring rate. it's a binary progressive compound spring basically.

[infiniti]

What color will the sorbothane landing pads be?

I'm just thinking of how these will work with LEDs and backlight keycaps.

[mkawa]

sorbothane only comes in black, and it's DENSE. 80lbs/ft3. you are not going to be able to see an LED through this. that said, if we diecut, we can cut around the led-sped, or you can manually punch a hole out with a pin and fit your led in there.

[damorgue]

I was under the impression that once Sorbothane has been deformed, it will retain that shape quite well. In our case, it would mean that it would be slow to recover and that the second key press on the same key will land on a far more depressed piece of Sorbothane. Key presses are sort of frequent so I don't think it will be very suitable for this application but I will keep track of your testing.

[mkawa]

it's a non-newtonian material like most visco-elastics. the deformation recovery rate and ultimate compression set depend on the shape factor of the material. check out the design guide: http://www.sorbothane.com/Sorbothane-Design-Guide101409.pdf

short answer: you can up the natural frequency by varying the geometry of the part, IF that's what you want. it is visco-elastic, but at such small sizes, the shape factor and other geometric design guidelines can flip with very small change in one dimension.

[infiniti]

sorbothane only comes in black, and it's DENSE. 80lbs/ft3. you are not going to be able to see an LED through this. that said, if we diecut, we can cut around the led-sped, or you can manually punch a hole out with a pin and fit your led in there.

Ah...I'll stick to clear/translucent white o-rings on my backlight keyboard but I'm still interested to try these out.  I'm still trying to wrap my mind around the feel you described. )

[MOZ]

Interested.

[Latin00032]

Interested

[nexus]

Interested.

[JayKthnx]

quite interested.

[mkawa]

found a die-cutter. prices look reasonable. going to have some samples cut and probably make a small experimental run

[JayKthnx]

let me know if you need a beta tester!

[Tarzan]

I'm curious if this material would be suitable for the "trampoline mod."  It sure sounds like it'd dampen the key impact, perhaps in conjunction with lengths of o-ring inside the stem...

[mkawa]

i actually have no idea what the trampoline mod is. checking that thread out..

[mkawa]

oobly's little rubber die spring is a helper spring that's internal to the stem housing. the problem with combining the two is that rubbers are basically all on the shore A scale and we're looking at putting 30 or 40 OO material on the keys here that engage at basically the same place that the 50-60A rubber would be engaging. the rubber die spring is going to _dominate_ the spring force.

another way to think about it that utilizes a keyboard analogy is thinking about the spring force of the rubber domes in a topre switch vs the spring force of the coil spring. the coil spring is literally only there to increase the decrease the capacitance of the assembly. the spring constant of the coil spring is an order of magnitude smaller than the spring force of the rubber dome.

note that this is a conscious design decision on tokyo press kogyo's part. they could tune the conductors below the spring to allow for much beefier springs, but they prefer that the switch have the force curve that the domes give. coil springs, especially the nested spring types they use, tend to be high force and digressive when used as actual springs, whereas domes are low force and progressive until they give way (due to air entrapment).

[Tarzan]

oobly's little rubber die spring is a helper spring that's internal to the stem housing. the problem with combining the two is that rubbers are basically all on the shore A scale and we're looking at putting 30 or 40 OO material on the keys here that engage at basically the same place that the 50-60A rubber would be engaging. the rubber die spring is going to _dominate_ the spring force.

another way to think about it that utilizes a keyboard analogy is thinking about the spring force of the rubber domes in a topre switch vs the spring force of the coil spring. the coil spring is literally only there to increase the decrease the capacitance of the assembly. the spring constant of the coil spring is an order of magnitude smaller than the spring force of the rubber dome.

note that this is a conscious design decision on tokyo press kogyo's part. they could tune the conductors below the spring to allow for much beefier springs, but they prefer that the switch have the force curve that the domes give. coil springs, especially the nested spring types they use, tend to be high force and digressive when used as actual springs, whereas domes are low force and progressive until they give way (due to air entrapment).

It'll be an interesting comparison.  Yet another way to "tune" a keyboard to fit one's specific likes.   

[mkawa]

it will certainly be another way to tune. that said, at some point too much tuning is kind of a pathology and no longer healthy

[Proc31]

I'm interested.

[RabRhee]

Interested in this,  Sorbothane is popular stuff in hi fi circles, I replaced the front end items feet with it. It apparently has extreme sound deadening powers so may have interesting results on a keyboard. Not seen any deform permanently, but maybe theres a process to reduce that.

[mkawa]

sorbothane can't absorb longitudinal waves in air aka sound waves very well, but it is _extremely_ good at dampening vibration in denser materials. because it's non-newtonian, it never pops back after being compressed without converting some of the energy that was used to compress it into heat. this is fantastic when you're trying, for example, to isolate your speakers from your desk to avoid nasty resonances or distorting reflections.

which actually brings up a good point. it's going to have the same effect on keys. the little sample i was playing around with completely eliminated the bottom-out sound of the key i put it on while leaving the faint 'click' of an MX blue.

interesting!

re: permanent deformation; i've sat around and calculated load tolerance with the application engineer and you'd have to put a lead ingot on your keyboard and stomp on it to damage the shapes we're looking at making.

[Jrwestcoast]

I'm interested

[RabRhee]

sorbothane can't absorb longitudinal waves in air aka sound waves very well, but it is _extremely_ good at dampening vibration in denser materials....

Aye, my bad, I meant vibration deadening, sound isolation. One of the mad turntable designers claimed that his turntable had something like -85 somethings(db?) isolation, -50 from sorbothane feet and -35 from his suspension setup. its impressive stuff

.....which actually brings up a good point. it's going to have the same effect on keys. the little sample i was playing around with completely eliminated the bottom-out sound of the key i put it on while leaving the faint 'click' of an MX blue.

interesting!
...

I was hoping it would do something like that. It could produce the a click as it is intended, for those heavy handed of us who don't click without thud.

[mkawa]

because it's non-newtonian it also makes a great spring damper. if one were to put a ring on the top of the stem's major diameter but underneath the switch top housing, it would dampen the rebound of the switch in the same way that the HHKB type-s pads do (but even more effectively). that said, if you did both the helper spring on the keycap and the damper on the top of the spring, you would give up 2mm of spring travel, minimum

actually, funny story. the first thing i tried with my small samples was to just jam it into the keycap. the key still actuated, but barely. there was like 0.05mm of travel. it was kind of hilarious. very quiet though!

[geniekid]

Interested.  I've tried three different kinds of o-rings and am waiting on two incoming sets of landing pads.  All of these were <$20 for 125 dampeners, so if the price is significantly higher than 16 cents per dampener people may need more convincing.

[heedpantsnow]

I'm in, if these get produced.  I'll even pay my way on a guinea pig run. This stuff is exactly what I'm looking for.

[Zeal]

it's really the same as any other landing pad, but softer. the idea is that instead of hitting a steel plate and pcb assembly when you bottom your keys out

Correct me if I'm wrong, but I was under the impression that keycaps bottom out on the underside of the stem, and not the bottom of the plate?

From my understanding, these sorbothane pads will go ontop of each switch, just like normal landing pads.
Just got a crazy idea -- what kind of sound dampening would happen if you were to cut a "skeleton-plate" of sorbothane so that the bottom of each keycap hits the sorbothane plate instead? I don't think this has ever been done in keyboard modding and I would think that it would dampen every keystroke a lot more than landing pads/orings can due to the high density and surface area coverage. The sorbothane plate would work like shelf-liner in aluminum cases, except it sits ontop of the plate & pcb. It would be able to dampen sound without affecting LEDs while being easier to install!

Very interested either way. I'd be willing to be a beta tester!

[tbc]

^ trampoline mod?

put something underneath the stem so the stem never actually touches the bottom of the switch housing.

[Zeal]

^ trampoline mod?

put something underneath the stem so the stem never actually touches the bottom of the switch housing.

In a way, I can see how they're relatively the same. However, having varying heights of the sorbothane-plate would be easier to swap out vs opening each switch and carefully placing a rubber blocker.

[tbc]

hm right, my bad.  you wouldn't have to desolder so that's a pretty big step saved. i keep thinking of building boards from scratch.

how important would it be that the material is perfectly sized though?  if it's too large and wrinkles, does that actually affect travel distance?

[Zeal]

hm right, my bad.  you wouldn't have to desolder so that's a pretty big step saved. i keep thinking of building boards from scratch.

how important would it be that the material is perfectly sized though?  if it's too large and wrinkles, does that actually affect travel distance?

I don't think it would be hard to get an accurate cut. From what I've read of the material, it seems fairly flexible.
I would assume that you can take a regular SS/Aluminum plate design and add 1-2mm spacing on all 4 sides.

[mkawa]

it's really the same as any other landing pad, but softer. the idea is that instead of hitting a steel plate and pcb assembly when you bottom your keys out

Correct me if I'm wrong, but I was under the impression that keycaps bottom out on the underside of the stem, and not the bottom of the plate?

good catch. hah! what i think i meant was that instead of the _slider_ bottoming out in the switch housing, the slider will float slightly because the keycap is not allowed to fully actuate (you will lose maybe 0.5mm oif travel).

[taylordcraig]

interested.

[NG7]

interested

[mkawa]

got the 1mm sample sheet today. it looks good, but will have an entirely different feel and probably a different shape than the .1" sheet.. will probably make two small dies to try out shapes and then make two large full-sheet dies if everything goes well..

[Melvang]

I so want to try these.

[Zeal]

got the 1mm sample sheet today. it looks good, but will have an entirely different feel and probably a different shape than the .1" sheet.. will probably make two small dies to try out shapes and then make two large full-sheet dies if everything goes well..

What are your thoughts on "sorbothane plate"?

Just got a crazy idea -- what kind of sound dampening would happen if you were to cut a "skeleton-plate" of sorbothane so that the bottom of each keycap hits the sorbothane plate instead? I don't think this has ever been done in keyboard modding and I would think that it would dampen every keystroke a lot more than landing pads/orings can due to the high density and surface area coverage. The sorbothane plate would work like shelf-liner in aluminum cases, except it sits ontop of the plate & pcb. It would be able to dampen sound without affecting LEDs while being easier to install!

[Melvang]

got the 1mm sample sheet today. it looks good, but will have an entirely different feel and probably a different shape than the .1" sheet.. will probably make two small dies to try out shapes and then make two large full-sheet dies if everything goes well..

What are your thoughts on "sorbothane plate"?

Just got a crazy idea -- what kind of sound dampening would happen if you were to cut a "skeleton-plate" of sorbothane so that the bottom of each keycap hits the sorbothane plate instead? I don't think this has ever been done in keyboard modding and I would think that it would dampen every keystroke a lot more than landing pads/orings can due to the high density and surface area coverage. The sorbothane plate would work like shelf-liner in aluminum cases, except it sits ontop of the plate & pcb. It would be able to dampen sound without affecting LEDs while being easier to install!

With as soft as this stuff is I wonder if you could cut a stainless plate a touch thinner and then cut a "plate" out of this stuff to match.  And have the sorbothane "plate" sandwiched between the stainless and the cap housing.

[Zeal]

got the 1mm sample sheet today. it looks good, but will have an entirely different feel and probably a different shape than the .1" sheet.. will probably make two small dies to try out shapes and then make two large full-sheet dies if everything goes well..

What are your thoughts on "sorbothane plate"?

Just got a crazy idea -- what kind of sound dampening would happen if you were to cut a "skeleton-plate" of sorbothane so that the bottom of each keycap hits the sorbothane plate instead? I don't think this has ever been done in keyboard modding and I would think that it would dampen every keystroke a lot more than landing pads/orings can due to the high density and surface area coverage. The sorbothane plate would work like shelf-liner in aluminum cases, except it sits ontop of the plate & pcb. It would be able to dampen sound without affecting LEDs while being easier to install!

With as soft as this stuff is I wonder if you could cut a stainless plate a touch thinner and then cut a "plate" out of this stuff to match.  And have the sorbothane "plate" sandwiched between the stainless and the cap housing.

But then you wouldn't be able to have variable sorbothane plates (EZ swap) in thickness without desoldering. I wonder what the difference in feel would be having it placed on a plate vs sandwiched in between plate+switch.

[mkawa]

one would go about making that sheet differently than o-rings or square pads, and it would have to be specific to the plate design. also i'm not really sure what it gets you that o-rings don't..

[Lengradde]

Very interested.

[mkawa]

learned some interesting stuff about designing for sorbothane. couple drawings going back to the board.. the 1mm thick is going to take some creativity..

[jacobolus]

I’m curious whether sorbothane landing pads will work for Alps switches, and if so whether their effect is pleasant. So I bought a couple sheets of 1mm sorbothane from ebay. We'll see what can be done with the stuff cutting out shapes w/ a utility knife, in a few days.

[Melvang]

How is the friction on this stuff?  I was thinking about using this stuff under the feet on my brushed behemoth.  The one problem is there is only going to be 2 square inches at most across all 4 feet, and with as much as this thing is going to weigh.

[mkawa]

your board will actually damage 1/10" or 1mm sheeting. you're going to want much thicker sheet. all duros (30, 40, 70 OO) are sticky and readily attach to smooth surfaces via stiction. they can then be held in place with small retainers on the corners, etc. however, you might want to look at the factory-produced pedestal mount parts, which have thicknesses of 1/4" up to > 1" in cylindrical form, instead of a pad. for your application they will be not only easier to mount, but they will probably be the only way to mount your board on sorbo without damaging it via compression set.

[Merloobi]

Interested! 

[MVPness]

I'm definitely interested in this.

[mkawa]

I’m curious whether sorbothane landing pads will work for Alps switches, and if so whether their effect is pleasant. So I bought a couple sheets of 1mm sorbothane from ebay. We'll see what can be done with the stuff cutting out shapes w/ a utility knife, in a few days.

this is basically what i'm doing at the moment. sorbothane is very visco-elastic. this is like putting more resilient and way denser memory foam in your keycaps. one has to be careful in designing the solid for the load and frequency or else you're either going to damage the sorbothane and render it useless, or it's just going to feel like crap, because it's always compressed and not absorbing any of the power you're putting into the keycap (which is the whole point here)

[jacobolus]

I bought a couple sheets of 1mm sorbothane from ebay. We'll see what can be done with the stuff cutting out shapes w/ a utility knife, [...]

this is basically what i'm doing at the moment. sorbothane is very visco-elastic. this is like putting more resilient and way denser memory foam in your keycaps. one has to be careful in designing the solid for the load and frequency [...]

What kind of shape do you cut, and where do you put it? I was thinking of trying to stick it on the top of the switch housing, around the slider, so that as a keycap is depressed it hits that (instead of the keycap hitting the housing top, or the slider hitting the housing bottom). Different keycaps are shaped differently on the inside/bottom, so it may work better with some keycaps than others. I’ll have to experiment a bit.

[mkawa]

if you read the design guidelines and ask some questions, what you'll find out is that you want as much surface area as possible that can "squish out". this means a couple things i hadn't expected:

1) you don't want a hole that's a close diameter to the MX stem. you actually want to make the inner hole significantly wider than the stem.

2) you want to use jagged cuts to your advantage.

3) you don't want to force the edges of the design into the edges of the inner keycap.

i've been playing around with pieces that go in the keycap as well as ones that go around the stem. there isn't a huge difference.. if the keycap internal surface is ribbed, you're just going to get a much different experience than if the keycap isn't ribbed. that's really where the difference is. this is true regardless of whether it's a stem mount or a keycap mount.

i do have an idea that may have some merit that is similar to the "trampoline" thing some people are playing around with, but haven't tried it yet. need some pin punches hmmmmmmm

[n0rvig]

if you read the design guidelines and ask some questions, what you'll find out is that you want as much surface area as possible that can "squish out". this means a couple things i hadn't expected:

[..redacted..]

i do have an idea that may have some merit that is similar to the "trampoline" thing some people are playing around with, but haven't tried it yet. need some pin punches hmmmmmmm

Yes! Keep up the crazy mad scientist sobothane research Kawa!

[mkawa]

anyone have a meat grinder or knowledge of general properties of threshing tools for soft materials?

[jacobolus]

mkawa: do you have any pictures of the shapes you’ve tried, w/ the sorbothane landing pads, ideally showing where/how you installed them, and some description of the effect?

[mkawa]

no, in fact i just tossed all my experimental parts into the trash yesterday. this followed a trip through the vitamix, in which the stuff just kind of humorously bounced around. the closest thing i've gotten to feeling reasonable is a 0.1x0.5x0.5" square with a hole in the middle and the edges sliced way down, all with craft knives and a steel probe.

the problem with this unit was that the helper spring kicked in almost immediately, as one can't make it any thinner than 2.5mm. it's ok if you're fine with almost scissor-switch like travel and then a very progressive damper at the bottom, but i wasn't personally crazy about it.

the 1mm thick material is almost impossible to design with. with thin material, what you want is really granular particles, almost like activated carbon. hence the blender experiment yesterday. this is because the guiding metric behind sorbo designs is, taking total surface area, loaded area (take one, cross-section, either top or bottom of the part) divided by unloaded area. the 1mm flat sheet, if cut straight, has 1xn mm unloaded area where n is the periphery of the part. so, if we design a standard washer with anything more than 1mm between ID and OD, our shape ratios (aforementioned guiding metric) become extremely high extremely quickly. high shape ratios are bad. low shape ratios are also bad. you ideally want between 1 and 1.3.

second problem. die cutting washers this small is extremely difficult. you're asking your diecutter for 1 thousandths tolerance basically, and that's like... most waterjets can't even do that, and your die is going to be really expensive on top of getting the die-cutter to hold the machine tolerance of the die.

a thresher that can process material and give it an average RMS diameter of like 100 mics (and we don't even care about tolerance as long as the particles are sufficiently granulated) will give you something you can place inside a switch, and the loose fill will keep the shape ratios of each particle about right. (again RMS average)

a meat grinder is a thresher with variable sized dies. you will need a strong traction motor (ie, your elbows + grease), but you should be able to machine a nice small diameter small particle die so that you can make a whole bunch of particulate matter in a few hours. that said, i have no other use of a meat grinder, and i have enough doubt that this will work to make this kind of ehhhh to me.

[jacobolus]

Hm. What if you glue a few little 1mm * 3mm * 3mm squares [or something] onto the cap bottom / switch housing top?

Edit: or better would be like a 3mm radius circle I guess (or slightly less). Then that would be top area of pi * 9mm^2, and side area of pi * 6mm^2, so that's 4/3 = ~1.3.

[mkawa]

then the entire surface becomes loaded and your shape ratio goes to infinity. das is bad.

[jacobolus]

I don’t quite follow. What are we trying to look for here? Percentage of the whole 3d shape that’s loaded? I thought you were talking about the ratio of top surface to side surfaces.

Doesn’t the amount of the load matter too?

[mkawa]

my understanding of the shape ratio is that it's a measure of compressive load to surface area, so if you have compressive stress on the object, you want to take the total area of compression (two sided) then divide by two, to be a bit more accurate. one can make the simplifying assumption though (note that shape ratio is totally a first order appx guideline) that all loaded area on one face is matched by loading on the geometrically opposite face. hence, take top of bottom.

because it's non-newtonian everywhere, then by definition there is no part of the stress/strain graph in which it can be linearly approximated, so rough guidelines are the word of the day.

and yah, the load and resonant frequency vs loading frequency are extremely important. the first of the first order calcs though is shape ratio. if your shape ratio is horrible, your design is bad and you're either not going to load the material at all and will see no benefit from it or you're going to destroy the stuff.

[jacobolus]

Did you try cutting shapes out of the 1mm stuff, and using them for landing pads? What was the result? [Or were your tests all inside the switch / with the 2.5mm sheets?]

[mkawa]

i cut a bit of 1mm off and put it in various places but was generally unimpressed by by attempts. the other thing is that some keys are ribbed internally, and actually underload the material. with the 2.5mm, this didn't matter, the sorbo would fill the key regardless. with the 1mm you had a choice between very little springiness and absolutely no springiness :|

[mkawa]

so, i don't see a way to get a pad into the space between the switcha and keycap. there just isn't enough room. however, a pcb mounted board with a large patterned pad that had isolated hemispheres until each key would work quite well.

[mkawa]

if someone is really interested in making this happen, has a copy of illustrator and can draw up a DWG with it against a phantom and gh60 board, i'm willing to make some prototypes. i have a pretty good idea of how to design for the material now, but the upshot is that you need to to take a relatively thick sheet and waterjet cut it so that it sits behind a (preferably pcb-mount) board's pcb. the non-conservative spring-like action will then happen between pcb and case. basically, you'll get very little resistance from the sorbothane as you press down on the keys, but when you bottom out, you will get a large helper spring effect both pushing back on your finger and absorbing the impact of your finger on the bottom of the switch. further, when you release the keyswitch, the sorbothane (with an appropriate amount of preload) will dampen any resonances in the switch/pcb/plate assembly. it will work especially well with PCB mounted switches and with switches plated in aluminum. some careful tuning will need to be done with regard to disc size under each switch, and switch thickness, however, but the effect should be quite interesting, certainly not like any switch-feel modifier people have used to date..

[jacobolus]

What have you actually tried here, mkawa? I’m a bit skeptical that putting something below the pcb (as compared to under the keycap or inside the switch) is going to have a huge impact on tactile feel, though I could definitely see it cutting out the noise.

In about 2 months, once I get back from a trip, I’m planning to join the SF TechShop and try CNC cutting some combined case/plates out of wood, to use with direct wiring. The idea is: take a solid piece of wood, as thick as you’d typically have for plate + pcb + the space in between, and then cut out the shape of the switch, such that it sits on top of a thin bit of wood at the bottom with a couple small holes for the leads, and the whole bottom half of the switch fits snugly encased (the exact 3-D shape to cut out needs to be figured out for each type of switch).

I’m curious if, in such a setup, a bit of sorbothane between the wooden shelf (standing in for a PCB) and the switch would have a useful effect here on noise/vibration damping. Then again, maybe there won’t be so much resonance in the wood slab to begin with.

[mkawa]

hardwood's going to be pretty dead as it is, but it definitely depends on thickness, finish, grain, etc.

done correctly, sorbothane can make things _extremely_ dead as far as vibration is concerned, and it can act as a spring when needed. the problem is that the spring constant (over its tiny tiny linear range) is due to the "bulging" of the material. you're displacing very dense, gel-like polyurethane, then, because it has very strong memory (unlike most polyurethanes), it pushes back. this means that very thin samples of material are pretty much useless, because they can't bulge. it also means you can't just put a mat down under something to dampen vibration unless that mat is much more of a cube than pretty much any mat is. i've worked with quite a bit of sorbothane bulk material. some of it has been effective, some of it has been damaged by me, and some of it has been for applications you normally wouldn't even consider offhand.

for the switches, i tried pretty much every variation on an o-ring or pad with a hole in it that i could think of. again, cubes work great, but they're huge, and cut stroke down to miniscule amounts. at 30 OO with room to bulge, there's still some travel from the spring action of the sorbo, but it was not something that i think anyone would like to type on. however, if you look at the keyboard assembly globally, which has impact frequency and location, things get a lot easier to manage. want room to bulge as a helper spring? make an appropriate series of cuts. want to just dampen? make a different series of cuts.

again, to design parts out of sorbo, you need do a fair amount of thinking about its spatial geometry both stressed and unstressed. the situation inside a keycap or switch is pretty much terrible. outside, things get a lot better.