revisiting MX footprints for plate mount

[Eszett]

Hi makers!  The drill holes for the MX's stabilizing legs are, if I'm not wrong, 4.0mm in diameter (for the large middle one) and 1.7mm for the 2 smaller ones. That means ZERO tolerance and makes sense for PCB mount, as it keeps the the switches tight and firm in place. However, I'm using plate mount, and I think for plate mount it's not only unnecessary, but unfavorable to have such tight drill holes. Because, as experience shows, it's pretty uncomfortable to assemble PCB + switches + plate with such a zero tolerance. Moreover, if there is even the slightest shift of a cutout in the plate assembly will be impossible. Yes I had this case and was shocked So my proposal is to englargen the drill holes of the PCB footprints for plate mount to 2.1mm and 4.6mm. For it brings an advantage in assembly, don't you think so? Your opinion please!
 

[0100010]

If one is using PCB mount switches with a plate, maybe.  If one is using plate mount only switches and had an alignment issue, could always shave down  that large pin on the bottom of the switch and finagle the contact pins a bit.

[joey]

I think it's hard to say without actually trying. If the holes are too big, they won't grip those legs at all, and make no sense to use PCB mount switches!

[Eszett]

I think it's hard to say without actually trying. If the holes are too big, they won't grip those legs at all, and make no sense to use PCB mount switches!

Well, we don't always have the choice to choose plate mount switches, since my Gaterons are sold as PCB mount (with those two extra legs) only!
And even if the holes are too big to grip the legs, there is no problem with that. If you want to have the PCB perfectly aligned to the plate you can take one single MX footprints (out of 70 or how many you have) and make it with tight drills (4.00 mm and 1.7mm according to Cherry specs), and the rest of the footprints with loose drills. By this you have best of both worlds: perfekt alignment and easy assembly!

[Data]

I'd think it's more important to get your plate made correctly than to sacrifice functionality and go outside the Cherry spec on the PCB.

The spec is ⌀0.157 ±0.004 inches (⌀3.9878 ±0.1016mm) so there is some tolerance built-in.  Adjusting that up to ⌀0.181 (⌀4.6mm ) is removing way too much material from the hole.  That's asking for trouble.

[Eszett]

Hi Data, what kind of "functionality" or "trouble" are you talking about? The holes have no function anymore, since the plate holds the switches tight. They are just there to give way for the legs ... The only minor "downside" is, that larger holes take abit more space for routing traces on PCB, but that isn't really an issue, since we are talking about tiny fractions of a millimeter ..

[Data]

Functionality is holding the switch in place, upright and square.  Plates are great for holding switches but mating them properly with a PCB really helps to reinforce their position & orientation.  There's also some friction from the switch peg that, along with the solder joints, helps to hold the PCB and support it as it hangs below the switch plate -- this is doubly true with PCB-mount switches. 

If you're designing PCBs exclusively for plate-mounted switches then you can eliminate the smaller side holes completely and enlarge the center hole all you want.  The important part is the solder joints, and you don't have a lot of wiggle room there.  If your goal is to add some cushion to the PCB to account for variations in plate design (which is how I'm reading your OP) then I'd say you're doing it wrong.  Stay within the spec if you need to add a little wiggle room, but concentrate on making plates that are sized correctly and this won't be a problem.

Enlarging the two smaller side holes for PCB-mount switches outside the Cherry spec effectively negates the whole point of PCB-mounting them.  That's a bad design choice.

[Eszett]

Functionality is holding the switch in place, upright and square.  Plates are great for holding switches but mating them properly with a PCB really helps to reinforce their position & orientation.

As said, the plate holds them in places, so there is no need to hold them by the PCB's drills. The solder joints are sufficient. The problem with this is that assembly isn't going to be much fun with drills of zero tolerance.

There's also some friction from the switch peg that, along with the solder joints, helps to hold the PCB and support it as it hangs below the switch plate

  I think the solder joints are sufficient to do the job..

If you're designing PCBs exclusively for plate-mounted switches then you can eliminate the smaller side holes completely and enlarge the center hole all you want.

Gaterons are AFAIK only sold as pcb mounts, so I can't eliminate the smaller drills.

Stay within the spec if you need to add a little wiggle room, but concentrate on making plates that are sized correctly and this won't be a problem.

Well, in an ideal world yes, but **** happens, and misalignment will shoot the whole batch.

[CPTBadAss]

I think it'd be cool to see you prototype it. Maybe you could buy some Enabler PCBs and drill the holes out to see if they work as you intend.

[Data]

AFAIK Gaterons (which I use) aren't sold as plate mount, so I have to keep all the drill holes. And having PCB mount switches with plate is a irregular situation, that is why I'm proposing these "irregular measures".

I don't think you're following this through.

What if someone decides to use your PCB without a plate?  He needs properly-sized holes to friction hold his switches, but you've gone and made them too large.

The PCB-mount pegs can be clipped off the switch housing for plate-mount implementation.  I had to do it on one of my Phantom builds.  It's not a big deal.

I don't want to come off like I'm ****ting on your thread.  I went through a similar situation a while back so I've thought about this quite a bit.  My conclusion was a bit different from yours.  I'll shut up now.

[Eszett]

What if someone decides to use your PCB without a plate?

Well, my keyboard is designed for plate only.

The PCB-mount pegs can be clipped off the switch housing for plate-mount implementation.  I had to do it on one of my Phantom builds.  It's not a big deal.

It may be no big deal if you assemble one single keyboard. But for assembly of 20-30 keyboards (as a small scale production) this is an immense work, since I have to clip them off and sand the remaining bumps afterwards too..

[Eszett]

An example. My plates here are with cutouts (MX&Alps compatible) from swills plate builder. When plugged in, the MX switches whiggle slightly on the horizontal axis by approx. 0.5 mm. Each single switch may be abit off and misaligned. So with drill holes of almost zero tolerance the consequence is that the PCB doesn't fit right away, but only with some time of fiddling around .. definitely not much fun. So my idea was to prevent any trouble that may occur due to misalignments of whatever reason.

Data, no emotions, just speak up whatever you like. 

[pomk]

Typically when you receive misaligned parts you get a total refund or new parts, making the issue quite moot IMO. Or if you find some manufacurer that does not give such quarantee, I would stay away from them completely. User error is also possible of course, but those are typically scaling issues or in 0.25U steps, both of which wont be fixed with this small changes. What about universal cut-outs and your design? I feel that you might end up with misaligned switches unless you take extra care when assembling.

[joey]

Gaterons are AFAIK only sold as pcb mounts, so I can't eliminate the smaller drills.

They are actually sold as plate mount too (e.g https://mechanicalkeyboards.com/shop/index.php?l=product_detail&p=1638)

[Eszett]

They are actually sold as plate mount too (e.g https://mechanicalkeyboards.com/shop/index.php?l=product_detail&p=1638)

Didn't know, thanks for correction!