I'm going to be using a layered acrylic case for the custom keyboard I'm designing. Trying to decide on a mounting plate thickness. Here is what I understand so far.
Thicker Acrylic Plate:
This is sturdier.
The switches are held in place by friction.
If hand wiring, Hot glue is recommended to hold switches in place. (I don't know if this is necessary with a PCB)
Questions:
Will a reinforcement layer on top of the 1.5mm switch plate work? It might need to accommodate the keycaps, not just the switch holes.
Does the decision affect overall case thickness? It seems like that extra support layer under the 1.5mm plate will leave less room for wiring and require thicker spacers. (hence the first question)
Is it difficult to get the switches glued to exactly the same height?
I am considering a price difference of <$20 between the two methods to be negligible. (i.e. hot glue, extra laser time, etc)
Here's the layout for which I am building the case.
(Attachment Link)
I haven't tried using 1.5mm acrylic, only 3mm Acrlylic. It flexes enough as it is, I can't imagine 1.5mm holding up very well. I think your layered approach will ultimately work out ok, but you'll obviously have to bond the plates together fairly consistently to gain the benefits.
Here's a crappy picture of what 3mm acrlyic looks like from the side:
There is about 1.7mm between the bottom of the acrylic and the top of the PCB.
You have ~3.2mm between the switches - that's a pretty narrow strip of acrylic.
With a key depressed, you have probably ~2mm clearance from the top of the plate, to the bottom of the cap. I'm not sure if that will be true with all caps.
So, theoretically you could build a 1.5mm plate with an additional 1.5mm layer both above and below that plate for a total 4.5mm thickness. That would probably be quite nice.
If you're going to try that, I suggest doing a trial run on something simpler (and even smaller) than what you have there. There is quite a bit of flex in
my 59% board using 3mm acrylic. It's not bad for typing, but when inserting the switches and putting on the caps, I had to brace the PCB underneath with my other hand.