Stop me if this already exists here, but so far I’ve only seen a few anemic reddit threads and one old Deskauthority one. I figured we might as well have a post about it:
I’ve wondered about the notch a fair bit. Older Cherry switches had taller ones, and older ones still had none - or instead of a notch they’d just have an ejection mark just like the circular ones usually found on the faces of stems. Here’s an image from Deskauthority of one of those:
I think you’re half right, @Backspace - but I think it’s actually the thin raised area around the edge that performs that function. It’s not super easy to see, but I believe the bumps on the inside of the cap stem here interact with those:
I think those begin too early for the notches usually seen on stems to interact with them. I don’t think all caps have these bumps, but I know at least a few do - and I’m sure most of you have experienced that snap-into-place feeling when seating some caps onto some (or even most) switches.
U4s (the silent ones) don’t have notches - but they do have raised edges and they taper. They’re widest at the top, and get more narrow towards the bottom - maybe this has a specific function, maybe it doesn’t - I honestly don’t know.
It’s not super obvious, but the silent U4 cross mount has an inverted cone thing going on.
So if its ribs and tapers that snap the caps, why the notch? I think that’s actually a recession to accommodate either a mold-ejection or sprue mark.
With that example early stem, the flash sticking out from that ejection mark will get mushed in the stem - probably not a big deal but even a little extra leftover there could cause problems for caps. Having it recessed makes that much less likely, or if it’s a sprue mark, negates the need for a trimming step.
Here’s an old Cherry of some kind with notches in two places and a taper (opposite of the U4’s) as well:
I think in the case of that switch, which apparently came from an Olympia typewriter, that bottom notch looks like it may have a retaining function, but who knows. The taller ones at the front (or sometimes back) may have as well, but I’m thinking those might just be recessed areas for ejection marks as well.
Not the best photo, but you might be able to see the mark inside the notch of this Dragonfruit stem (in a Nebula housing):
A Nebula stem (in an Azure Dragon housing) - this one has more leftover flash so it’s easier to see:
Here’s an Epomaker stem (in a Tecsee Corsa housing) with no front or back notch, but a recessed area in the top-center to accommodate an ejection or sprue mark:
But hey! Here’s a Tecsee Corsa stem (in an Epomaker / Skyloong housing) and it has a notch but no mark inside.
(Edit: forgot that photo!)
Maybe it’s there because Tecsee saw it on Cherry and other stems and figured it has a function other than shrouding flash - or maybe it does have a retention function and also just happens to be a convenient place to shroud flash.
I’m mostly speculating here - any switch sages able to weigh-in on the matter?