plate materials

[Rider87]

Hi, I would like to talk about this again.
No one told about vibrations generated after click, this is something that I don't like and I think that mounting plate can damping or inrease, depending of material and thickness used.
So for my next project (with blue alps) I would like to use a soft metal to mounting plate, in this case Tin-lead for soft solder (60%Sn 40%Pb). What do you think about this? god idea?

Regards!

[Findecanor]

I believe that for sound what matters most is how the PCB and plate are mounted inside the case.

[codemonkeymike]

Isn't Tin and Lead alloys what are used for organ pipes? The alloy is meant to be extra resonant, so maybe not the best choice. If you want something soft and affordable you could do Acrylic or PCB material.

[mhinsch]

I'm using a 1mm aluminium plate for my current (and first) build. It's wobbly as hell but luckily I planned in plenty of standoffs. When they are properly attached to the switch and bottom (2mm alu) plate the keyboard feels very solid and I can detect no vibrations or resonance. For further dampening and stabilizations and to attach the frame I will also put some rubber bumpers between the plates - that should really take care of it. So, to sum up - with proper structural support I think you won't hear the material of the mounting plate.

[Rider87]

I believe that for sound what matters most is how the PCB and plate are mounted inside the case.

Yes, I'm sure that it's very important. In this case plate and case would be a single piece made by casting, 3mm thick, without pcb, wired by hand.
Something like this:

Isn't Tin and Lead alloys what are used for organ pipes? The alloy is meant to be extra resonant, so maybe not the best choice. If you want something soft and affordable you could do Acrylic or PCB material.

An interesting answer, however I am not sure that is the reason. For example, I know that indium-tin alloys are used specifically for damping (but I do not have access to them).Damping materials have different attenuation to different frequencies, this may have something to do with his use for musical instruments, maybe they are tring to damp specific frequencies. Realiy I don't know...

Another thing that I am sure is that when I hit two bars of SnPb I can clearly feel that propagation of the vibration is remarkably lower than any other metal I have had in my hands.

I'm using a 1mm aluminium plate for my current (and first) build. It's wobbly as hell but luckily I planned in plenty of standoffs. When they are properly attached to the switch and bottom (2mm alu) plate the keyboard feels very solid and I can detect no vibrations or resonance. For further dampening and stabilizations and to attach the frame I will also put some rubber bumpers between the plates - that should really take care of it. So, to sum up - with proper structural support I think you won't hear the material of the mounting plate.

Yes, probably isn't necessary be so complicated, a good construction should be enough.

However, one of the reasons why I would like to try it is because I have never tried metal casting before, this could be a good moment

There are other materials that I would like to try for the cushioning, aramid or flax fiber whit cork core material are materials specialized for damping in composite material aplication, so it should be better than PCB (fiber glass), or carbon fiber (if you are looking damping)

[Rider87]

Here first test:
Really a test to probe manufacture viability, with this thickness and size it wouldn't be right to do compilations with other materials.




About manofacture, it's probably too complex to develop a full keyboard ...

[ag123]

hi just like to bounce this thread with a question.
i think steel and aluminium plates are good as they fit those 1.5 mm snap-fit grooves on cherry and/or gateron switches.
however, steel / aluminium other than being rather expensive also requires high power industrial lasers that metal fabrication shops uses.
there are a lot of shops with low power laser cutters suitable to cut acrylic, but as acrylic is much less stiff than steel / aluminium, has any one has much success using acrylic plates of 4-5mm thickness for a friction fit of those switches?

i'm thinking of making a plate based keyboard without the pcb hence this plate is the key to hold the keys together.
it would be a disappointment if after spending the $ getting the switches etc & it turns out with keys that comes loose easily from the plate. i'd not want to use glue but short of that i'm not sure how i can hold the keys to the plate other than friction fit

thanks in adfvance
cheers

[zool]

Sure you can, but you have to stack or find a sheet that is the thickness of the switch to the pcb, otherwise the pcb can move about, and you don't want to put too much pressure on the sides of the switches as that can change the characteristics of the switch itself.

I'll also point out standard FR4 pcb materiel is the right thickness for a plate. and you can get them made cheap enough or cut with low cost tools.

[Findecanor]

however, steel / aluminium other than being rather expensive also requires high power industrial lasers that metal fabrication shops uses.

Plates in DIY kits are often milled, and with small milling bits to get tight corners.
However, you don't always need that precision. You can go up in corner radius if you modify the shape of the hole.

I believe larger product runs are stamped / broached. For these there is a larger initial cost for the tooling but in total a smaller cost per plate because of volume.

[ag123]

on re-thinking i think there is a mod to secure the keys to a thick (e.g. 4-5mm) acrylic plate which is possibly lose fitting, it is to use something to secure the central post to the plate, but this would require a mod, or some kind of fixing pins that can be used at the central post to secure to the plate, do such pins exists and can be bought on ebay etc?
short of that may be to drill some holes on the central post and perhaps run a rather thick wire through it but the thickness of the acrylic would need to flush to about level with the base of the switch

the idea is to just have the acrylic plate to hold the keys in place, no pcb below, the connections are plain wires and can be routed to say a small mcu board running say some kind of arduino setup

while searching around the web i stumbled into
http://thume.ca/2014/09/08/creating-a-k ... -hardware/
a good attempt with acrylic:

After adjusting for the kerf I had to figure out how tight I wanted the switch holes. Here are the results of my testing, measured against the Cherry width spec of 19.05mm with calipers:

-0.15mm : Very loose fit, some play, can't pull keycap without pulling out switch.
Keyboard made like this would fall apart easily if it didn't have a PCB.
-0.10mm : Same as -0.15mm maybe imperceptibly tighter
0.00mm : Cherry Spec. Holds switches to be very robust without a PCB. Almost zero play.
Still not tight enough to pull a keycap without pulling out switch.
+0.05mm : Very nice solid fit. Can pull a keycap off without pulling switch.
+0.10mm : Quite tight without stressing switch.
Can easily pull keycap off without feeling switch move.
Takes effort to pop out.
I'm going to use this for my board since it won't have a PCB.

For my final version I decided on the +0.1mm inset (0.3mm including accounting for the laser kerf.).

friction fitting the switches meant playing with the laser cutting kerfs to tolerances of 0.05mm
only thing would be that it may come loose after some time my guess is the polymers may yield and stretch somewhat over time.

[ag123]

hi, i'd just like to ask a different question, this time aluminium
shops with CNC routers seemed rather common to find (e.g. those who make signboards may have them)
i watched this video on using a CNC router to cut an aluminium sign
https://www.youtube.com/watch?v=x5GzCdKhxmQ

now my question is are the normal CNC routers adequate precision to cut 1.5mm aluminium sheets into (cherry) keyboard plates?

thanks in advance

[zool]

hi, i'd just like to ask a different question, this time aluminium
shops with CNC routers seemed rather common to find (e.g. those who make signboards may have them)
i watched this video on using a CNC router to cut an aluminium sign
https://www.youtube.com/watch?v=x5GzCdKhxmQ

now my question is are the normal CNC routers adequate precision to cut 1.5mm aluminium sheets into (cherry) keyboard plates?

thanks in advance

It varies so widely, but in general yes. you need to pay attention to the corner radii if you get a plate routed/milled or come back in with a file and square them off.

[pomk]

hi, i'd just like to ask a different question, this time aluminium
shops with CNC routers seemed rather common to find (e.g. those who make signboards may have them)
i watched this video on using a CNC router to cut an aluminium sign
https://www.youtube.com/watch?v=x5GzCdKhxmQ

now my question is are the normal CNC routers adequate precision to cut 1.5mm aluminium sheets into (cherry) keyboard plates?

thanks in advance

What do you mean by ’normal cnc routers’ ? Hobby routers might not have high enough repeatibility for that, but any industrial one will be easily accurate enough. A 2mm tool is small enough that you would not need any additional corner processing.

[ag123]

Thanks! as i've approached a workshop who has some 'sexy' high power laser cutters who quoted the price of cutting a metal plate that i could probably purchase a dozen quality 104-108 keys mech keyboards. hence i searched for alternatives, i'd put cnc routing as a good alternative with aluminium plates

i'm familiar with acrylic and laser cutters (many signboard builders have them, not just the specialised workshops)
and i still think laser cutting acrylic plates is a good moderate (possibly low) cost and high precision means to cut keyboard plates. it is almost 'plug and play', nearly as simple as http://builder.swillkb.com configure the plate, get the cad, send to laser cutter cut it on acrylic plate & you're set to build the keyboard

the biggest headache is that (cherry) (& clones) keyboard switches are possibly never intended to be simply mounted with thick (3-5mm) acrylic plates, and be simply used to hold the keys *without a pcb* and one may be forced to use glue (e.g. hot melt) to bond the switches to the plate that could mean it is near impossible to remove and swap defective switches. I’m still trying to find a good solution keep the switches well mounted on thick acrylic plates without glue and without pcb, effectively the plate is the keyboard.
the other thing is that acrylic plates possibly won't last as well as metal plates ,possibly giving problems rather early into routine use, but basically that's the cost - performance trade-off

on a side note there is a side benefit of using *thick* acrylic plates (but could be any other materials)
the stiffness of rectangular plate varies proportional to the cube of the thickness
https://en.wikipedia.org/wiki/List_of_s ... ts_of_area
using a thick (acrylic) plate would give a very firm keyboard on its own without a pcb despite the large and many cut outs for the keys e.g. in a full sized 104 keys keyboard

[zool]

Getting a 1.6mm 316 stainless steel plate laser cut should cost less or around $100USD.
1.6mm FR4 PCB plate can cost as little as ~$4USD per piece in small qnty(5off). quite stiff. alot stiffer than say 3mm acrylic.
CNC machined mono plate 6061T6 aluminium $250USD+. 1off

[ag123]

Thanks i found another source of laser cutting aluminium plate. The shop quoted a more reasonable price like mentioned.
Some what off-topic but may be useful

The stiffness of a plate is proportional to the young's modulus multiplied by moment of inertia of the cross section, the moment of interia is proportional to the cube of the thickness this makes for some rather interesting comparisons
https://en.wikipedia.org/wiki/Bending_stiffness
then getting the material young's modulus
https://www.engineeringtoolbox.com/youn ... d_417.html
I did some calcs / comparisons and it comes out as follows:

Code: Select all

          	E	h	Eh^3
aluminium	69	1.5	232.875
acrylic  	2.9	4	185.6
acrylic  	2.9	5	362.5

h is the thickness in mm
This sort of says that a 4mm acrylic plate is about as stiff as a 1.5mm aluminium plate
and a 5mm acrylic plate is stiffer (considerably) compared to a 1.5mm aluminium plate (despite the young's modulus of acrylic 1/20 that of aluminium) !

For large long keyboards without a pcb a thick plate would likely help
For those extemely hardcore they could possibly reinforce the bottom bending surface with carbon fibres and my guess is they may be able to make a 1.5mm acrylic plate that's as stiff as steel