Z Axis on the knee

This has been done many time before so I can't see the problem.
Here in the UK in the late 80's the bigger knee mills had 4 axis control
of the bed. X,Y,Z were the usual axis moves and W was designated to the
knee. Most also had A and B rotary moves.
Among the makers who offered this were Matchmaker, Acton and Beaver.
It's main use was not so much for increased Z hight as most of these had a
full 8" movement anyway, but tool changing.
Imagine doing a mould for a saucepan. You have the tool at full reach in
the bottom and need to change tools. Even at full retract the tool changer
will hit the mould so at tool change time the W would drop the knee, swap
tools and then raise it back up to where it needed to be for the next tool.

I am just scrapping a big Acton that had just this arrangement on it. Ball
screw on the knee and a big Superior 1100 oz in motor, no gas assist,
nothing else and this baby weighs in at 3.5 ton. The knee and bed assembly
is heavier than a complete Bridgy.

John S.
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Regards

John Stevenson
Nottingham, England