deskthority

I know the reason behind PCB mounting pins - they are meant to keep the switches aligned so that they don't wobble during assembly. But are those really necessary? If the holes for the switch contacts and the large 4mm cetral hole for a MX switch are drilled with reasonably tight tolerances, shouldn't that be enough to properly align the switches? That way you could avoid the PCB/plate mounting confusion and simply always use plate mounted switches.

Has anyone tried this?

The reason I'm asking this is the M9 switch that 7bit is selling for 0.10EUR a pop. It's a plate mounted switch and doesn't even have the central 4mm plastic pin. But the contact pins are very far apart (~12.5mm), and that should be enough to align the switch if the holes on the PCB are just wide enough to fit the contact pins. They should align the switch with enough accuracy.

Cherry MX's electrical pins are flat, so they are quite loose. The mounting pins are made to friction-fit into the circular holes in the PCB. A switch without them has a larger risk of falling off.
I don't think it is just about assembly but about adding stability overall, prevent the switches from being twisted and as both pins are on the same side of the centre, also about preventing the switch from being overturned with the legs being bent.
That said, I have had a keyboard with no plate but switches without mounting pins, and it worked OK.

Cherry's pretty smart about handling off-axis key presses. (Especially compared to Alps.) MX switches behave themselves quite well when subjected to really nasty, sloppy typing. The mounting system design is probably another piece of that same puzzle: belt and braces.

I splitted a space bar in four with no mounting pins in two switches and it works well. As said, the central plot is really important and do a part of the job so I wont risk this lazy PCB mount with M9 or Alps.

Yes, I think I'll stick with the MX for a while longer.

Thanks for the replies!

the mx pins are flat and rather sharp. If the hole is small enough the pins "cut" their way in and the switch doesn't come off even if the PCB is turned outside down. That being said I did that on cherry mx blue and they have at least a the central plastic bit. I have no clue about M9.