Plate thickness/material recommendation?

[flabbergast]

I'm thinking about making a small board for ALPS switches, and I've got a plate design conundrum: From what I read, ALPS switches should use a 1.2mm thick plate. Now I'd like to use aluminium for the plate material instead of steel (personal preference for the keyboard feel).

For the case, I would just like to use another metal plate, attached to the top plate by standoffs - "handwiring-style". I do not particularly want the bottom plate to be aluminium as well, although it would be nice; this time mainly for weight. This one can also be thicker, I'm thinking 1.5mm minimum.

I do plan on making a PCB for this. This means that theoretically I can design it more-less the way usual 60% keyboards are, namely the top plate would just have large holes, and only the PCB would be attached to the bottom plate, via standoffs. However this approach has a few problems in my setup, namely that the bottom plate does not have support fins, and I don't think I can find enough space on the layout to make big 5mm holes in the top plate (i.e. the space between normally spaced switches is not big enough, and there aren't sufficiently many large spaces at all the places I would like to place the standoffs).

So - do you think having a 1.2mm alu top plate attached to the bottom plate via 5 standoffs would be strong enough for this? The layout/size is this (the holes are currently 2.8mm; the vertical distance between rows is 6.25mm; the horizontal between 1u switches is 3.45mm):

Other thoughts/recommendations? Thanks!

[Matt_]

I do plan on making a PCB for this. This means that theoretically I can design it more-less the way usual 60% keyboards are, namely the top plate would just have large holes, and only the PCB would be attached to the bottom plate, via standoffs.

If you mean like this:



it looks like the most straightforward way to do it, but I am not sure I understand what prevents you from doing this. Are Alps switchs so wide that you cannot fit a hole for a 4 mm screw head between two of them? BTW, here is how they do on a typical (MX) 60%:



As long as switches are held by the four corners it should be okay to have one side missing, even with 1.2 mm alu. If there really is not enough space between columns, it should be safer to place screws between rows as you did. The locations you chose may work, but I would shift them so that holes do not eat into switch corners, perhaps more like this:

[flabbergast]

Yes, the first picture of yours is exactly what I meant (nice pic!).

Yep, the ALPS are too wide - there's only 3.45mm between the switch holes horizontally, even less between the actual switches because they have "wings" that latch onto the plate on all 4 sides (well at least the matias switches that I can check right now do). It might work vertically (there's 6.25mm space). I would need about 5mm holes, right?

The thing I was afraid of is whether 5 screws+standoffs like you draw would be enough support for the PCB. I thought that Cherry keyboards built like this have "fins" built into the bottom case, i.e. horizontal bars, so that the PCB actually sits on those, and not just on the few standoffs for screws.

EDIT: It occured to me to check how does planck do it, and Jack apparently went with the first option I described: the standoffs are between the top and the bottom plates, and the PCB just "hangs" on the switches. It's visible on his photos. But the planck has 1.5mm steel plate...

[Matt_]

Yes, 5 mm holes would be about right for M2 screws (the head diameter is slightly under 4 mm).

I think it's okay for the PCB to just rest on standoffs. I suspect that fins on the bottom of cases are more for rigidity than support (you would have to make sure that they won't interfere with components under the PCB). Typical 6°% boards have six standoffs arranged in an uneven pattern:



You could add a sixth one in the center to be sure it's more stable:



Not sure if that would be necessary but if you have enough space, it wouldn't hurt either

edit : Jack's solution works as well, you would have smaller holes in the top plates but bigger ones in the PCB. Not sure there would be a big difference regarding rigidity. Also you would have to make sure that screw heads are low enough so as not to interfere with pressed keycaps.

[flabbergast]

The screws interfering with the keycaps is not a problem (I'm looking at some right now; and also I built a planck some time ago and that wasn't an issue).

It's again a question of sufficient support/strength: I'm afraid that 1.2mm alu plate might bend/tear around the standoffs and/or edges if someone presses the keys hard enough.

[Matt_]

I frankly doubt that 1.2 mm alu would tear around the standoffs, unless perhaps you bang your keyboard unreasonably hard — and then you'll probably break something else before breaking the plate. It would feel a bit more springy than 1.5 mm alu and even more than steel (especially near the edges), but I guess that's the reason why you chose alu in the first place.

I have a few sheets of alu on hand, but unfortunately not in 1.2 mm thickness. 1.0 mm feels a bit too light/flexible for a plate, but I can't even see it tearing as you describe.

[flabbergast]

Thanks! Well I guess I'll just have to try

Yes, I prefer alu because it's less stiff than steel - I've had an infinity with the bent steel plate, and that was way too stiff for me, my fingers were hurting. I guess also the fact that the sheet was bent contributed to the stiffness though. I have now a keyboard with matias click switches and 1.5mm steel plate and it's OK (but it's clear that the switches are not completely latched onto the plate, 1.5mm is too thick).

[Matt_]

Maybe 1.2 mm steel would be a safe middle ground? Stronger than 1.2 mm aluminum, but probably less stiff than 1.5 mm steel. Also keep in mind that there are several grades of alu and steel, and that some are harder than others, which may come into play. Check what your plate cutter can provide you with.

In any case the Planck construction should be the best solution for you. Smaller holes and better plate support.