This time, we're sure we've got it right. Only because, we couldn't have come up with a more difficult-to-implement solution! We're (slowly) removing each pad - yes, complete with linkages and springs - and fitting a pushbutton under each one.
In doing this, we're finding out quite a bit about the saxophone.
Namely that it's been badly dropped at some point during it's life, and would be unplayable as an acoustic instrument! There are four or five pads misaligned - and rings on the leather showing where the pad used to sit, and a shallower indent showing it's new resting position after the (presumed) accident.
So despite filling the body with hot glue and generally making a mess of things, at least we can be satisfied in knowing we're not ruining a perfectly good sax for this project - it was only destined for a junk shop somewhere, or an expensive repair job!
(Saxophone fitted with five pushbuttons, mounted into acrylic disks. The push buttons are the slightly clicky tactile ones and the guard has been removed to allow the pads to open more fully).
However, some pads are "normally closed" and open when you press a key (or combination of keys) rather than the simpler push-to-close type. We found that sometimes, if you release a key gently, the spring on the pad isn't always strong enough to force the pad fully closed again. Here's an example of one such pad. An extra spring was added between the pad cover and the guard, to help push the pad into it's normally-closed state, and force the pushbutton to "click closed")