I suppose I should delve into the layout options and pretty this up a bit. But not today, because I'm feeling pretty rubbish today and don't feel like thinking.
Well, the Mk1 air valve worked but wasn't very precise. The Mk2 didn't get a lot further. Currently on Mk3.

The MK3 is still WIP, but it will fit inside the bass end of a mini-melodeon.

The narrower slot on on the right guides the lever to stop it moving around too much. It is actually a tad too wide, but it's staying that way. The LH side allows a fixing screw, but it will be glued - the screw is just to keep it still while the glue dries. Lot easier than trying to clamp it. But it needs some tidying up first.

The other one is a spare in case I cock up the first one. As if :-) (I started with three spares...)

The lever is made, the spindle (3mm stainless rod) too. I need to make the spring, 0.55mm piano wire (some may recognise that gauge). Making it is fairly easy, fitting it to the spindle is a pig. Later.

I have marked out where to drill the bass casework. I think I can manage a 10mm hole, still deciding whether to make it round or oval.

Anyway, that's up to date. Nothing more will happen for a few days at least, partly because I'm suffering from a bug but mainly because the weather has turned cold and my garage isn't heated.