Cutout profiles

[pev]

Hey all!

Long time listener, first time caller... Im having a crack at putting together a prototype layout to see how I feel about it. I'd like to test layout by using 1.5mm acrylic to make a test panel mount plate using my desktop CNC router.

I've seen a whole bunch of conversations about cutouts but both cherrys cutout and most Ive seen suggested are square cornered but of course router bits are round... I expect I'll be using a 2mm cutter smallest which means external corners would be 1mm radius round. Has anyone experimented / had success with hole shapes taking a cutter shape into account?

Thanks!

[suicidal_orange]

The switches fit tighter to the corners than a 1mm rad will allow so you'll have to drill an extra hole outside each corner to fit them in.  As long as the sides, top and bottom of the hole are tight to the switch this won't cause you any problems.

Good luck

[Leslieann]

No need to drill, you just add a little clover leaf to each corner.
Same as drilling, but  no tool swap necessary.

[pev]

Ah thanks - I guess you mean running the tool straight into the corners though? The cherry datasheet indicates that you should use 'tab' shaped edges though, do you know why this is? Looking at some switches it isnt obvious...!

[katotaka]

This is what I used in a few projects


while the relief cuts account for the router bit they also allow cherry(&clones) switches to be opened without being removed from the PCB

[Findecanor]

There is also the leaning H-shaped cutout, which I once proposed precisely for CNC-machining with thicker routing bits, while allowing a (Cherry MX) switich to be opened without removing the bottom from the plate/PCB.
Tests showed that it requires tighter tolerances than other shapes though.

Edit: katotaka beat me to it, by a few seconds.

[coarse]

no one's pointed it out yet, so let me be the one to do it

1.5mm acrylic plates shouldnt be used as is. youll need a 3mm plate below to support the switch plate

[katotaka]

last time I ordered 3mm thick CF plates with 1.5mm cutouts to clip the switches in place


the vendor uses 1.5mm bit, I left the corner as-is and just jammed the switches into the openings
note that it will shave some plastic off the corners but the switches are very secure now

[suicidal_orange]

the vendor uses 1.5mm bit, I left the corner as-is and just jammed the switches into the openings
note that it will shave some plastic off the corners but the switches are very secure now

Good to know 1.5mm just about works, though even with the smaller bit a 1.5mm acrylic plate would break before shaving the corners off a switch.

Ah thanks - I guess you mean running the tool straight into the corners though? The cherry datasheet indicates that you should use 'tab' shaped edges though, do you know why this is? Looking at some switches it isnt obvious...!

You could just run into the corners, whatever's easier.   The extra gaps at the sides of the switch on the datasheet are so you can pop the top off the switch without desoldering and removing it from the plate.  Not all MX clone switches support this so check first - no point wasting time on complicated cutouts if you don't need to.

[katotaka]

you better off incorporate some sort of certain mouse ears kind of relief cuts

and the cuts should be a tiny bit bigger than your bit, so the CAM toolpath creates a tiny U-turn instead of jamming it into the corner creating a high sideway tool load

[Leslieann]

last time I ordered 3mm thick CF plates with 1.5mm cutouts to clip the switches in place

the vendor uses 1.5mm bit, I left the corner as-is and just jammed the switches into the openings
note that it will shave some plastic off the corners but the switches are very secure now[/b]

This is bad...

For one it can distort the switch housing causing binding and fail to properly lock in place, but the other issue is carbon fiber is layered and while strong you can actually cause it to start to delaminate doing this.

It's strong but only in certain directions, this is where it's the weakest. Will it matter? Depends if it spreads and how far it goes. It's not likely to really make a difference in feel as it's still strong but it can cause weird harmonics.

[katotaka]

The corners could be potentially bad, but turned out no perceivable difference, at least for the one I'm typing on.

For the latch locking scallops, at worst the plate just partially delaminate at the cut depth around the cut, and fall back to 1.5mm stiffness for that particular area - maybe somewhere between 2 or 3 switches, who knows?

CF sheets are strongest sideways like hitting it like a knife, but it doesn't mean that it would explode on its own if attacked at the top/bottom

[pev]

no one's pointed it out yet, so let me be the one to do it

1.5mm acrylic plates shouldnt be used as is. youll need a 3mm plate below to support the switch plate

Ah good spot - yes, these are initially just for layout prototyping / testing, my plan was once I was happy with layout feel that I could get replicas laser / water cut from 1.5mm stainless using the same DXF source for actual usage. I assume that that should work OK?