5 pin MX footpint holes are too big and not interfacing with extra pins

[ChrisChrisLoLo]

Similar to #38, I've found that the holes in the 5 pin MX footprint are too large, particularly with the extra pins. Right now the extra pins are loose and not interfacing with the PCB, which puts all of the friction force on the main pin and the hotswap contact points. The consequence for this is that I am unable to use these footprints for gasket mount pcbs, since they require the friction force from the extra pins. This footprint may also not be suitable for plateless builds.

The diameter of the footprint in this library uses 1.75 mm, and I've confirmed with calipers that the pcb from the factory has similar if not the same diameter.

Looking at other libraries like https://github.com/daprice/keyswitches.pretty/tree/master, they seem to be using a diameter of 1.7018mm, which has worked well for my previous projects. This matches what's outlined in this schematic here, which specifies that the security pins are at most 1.7 mm (with a tolerance of down to 1.65 mm).

Could we reduce the security pin diameter down to 1.7mm for the MX footprints?

[ebastler]

Hello,

I have been using these footprints for a (very) long time now, and never had issues with loose switches (actually, some switches like Alpacas I struggled to force into PCBs with 1.75mm before).

I can not remember when and why I opted for 1.75mm over 1.7mm, but I am fairly certain it was a deliberate decision, and I am hesitant to change footprints that have proven themselves.

You say you have tested 1,70mm before and it worked fine?

[ebastler]

@MarvFPV what's your opinion on this? Can you remember why we opted for 1.75 back then? How would you proceed?

[Marbelymarble]

@MarvFPV what's your opinion on this? Can you remember why we opted for 1.75 back then? How would you proceed?

It seems we did it to match the most prominent lib at the time (ai03).
@ChrisChrisLoLo did you check with multiple different switches and manufacturers? I also have never had issues with the friction fits on my boards.
@ebastler do you think it could've been for tolerance issues with the more affordable board fabs back in the day? The MX footprints were created ~4 years ago and the lib they're based on is even older.

I'm also hesitant to change them, maybe we could gather feedback from current users? The mx footprint is a core part of the library that i wouldn't want to touch without more information.

[ChrisChrisLoLo]

Hi all, appretiate the effort looking into this.

For data, yes, I have tested 1.70mm with several switches before. Switches I've used with this dimension include ones from Gateron, Kailh, Akko, Gazzew (Outemu). I have not had tolerance issues with these switches, the hole was big enough to add additional friction to the switches, but removing or pushing the switches were not an issue. I've used fabs from PCBWay, JLCPCB, and SeeedStudio

[ebastler]

Thanks for your feedback! I checked our old chat logs and it was a deliberate decision back in the day, but I can not remember why we did it anymore.

could've been for tolerance issues with the more affordable board fabs back in the day

Might be the reason - IIRC JLC had pretty big tolerances back then.

I'd like to think about it for a bit still, but IMO it would make sense to switch. I just tested a new batch from JLC with 1.75mm holes, and switches don't sit loosely, but they also don't grip as tightly as I'd like them to indeed.