As the G#-mechanism is simplest to illustrate the general working of my switch mechanisms, I will use it here. I take the example of the mechanism built for the tenor.
|The block slides between two the sheets of the switch (a bit hard to see). The block sits on the spindle of an excenter. The excenter takes care of the regulation: to close the two keys exactly simultaneously.
In the ideal situation, the hinge of the switch in rest is perfectly in line with the hinge of the driver. In the case of the G#-mechanism in an average modern lay out, this is indeed possible. Also, and again ideally, the spindle, the hinge and the fingertip are in a straight line.
Next, the hinge of the switch only has to make only about half the movement of the keycup, otherwise the fingertip of the switch would make excess sway compared to the key, resulting in a bumpy feeling when operating the mechanism. This 'half the movement' necessitates that the hinge of the G#-lever is moved to a place further away from the hinges of the B and Bb spatulas. Also, the movement of the finger of the switch can be regulated by the amount of length of the excenter chosen on the driver (you cannot see this, but the driver has a slit to pass the bolt through).
The sway of the switchlever also has to be limited. Now, in the case of the G#-mechanism, both upper and lower limits are already given, but in the case of the open-key mechs for keys nrs. 3 and 5, this limitation of movement requires some extra attention.
This G# does not offer any added fingering possibilities, but could do so if we would split the mechanism of key nr. 12 in two parts along the green and purple lines, separating the functions of the third finger left hand to the driver from a hypothetical «petit-fingering» for the second finger to the key cup itself – which would in this case produce a P-fingering for Ab (!).
|This is essentially what I did in the added «petit-fingering» for Eb for the second finger right hand in both the tenor and soprano saxophones.
The touchpiece for the third finger is linked directly to the driver only, taking key nr. 6 along in its movement (not unlike the mechanism for alternative Eb in the 20s Bueschers and Conns). Next, this driver operates key nr. 5 via the switch and the hinge of the switch in its turn is operated by the D#-touchpiece.
Similarly in the soprano, the function of the pushing down the touchpiece of the fourth finger right hand was separated from key nr. 4 and directly connected to the driver only, allowing for an added Db-touchpiece which is now linked to key nr. 4. The linkage between keys nr 2 and 3 makes that you can play directly from the new Db to low-B or to low-Bb with the fourth finger left hand only.
The conventional C#-spatula operates the hinge of the switch and here fingering remains as it is.
I hope you now better understand how it works. The open key mechanisms for keys nrs. 3 and 5 (both in the curved and the straight instruments) are rather more complicated to make than for key nr. 11 (which does require a bridge to relocate its hinge, though) and for the curved instruments require some adaptations, though they are essentially similar.