I'm seeing lots of post on other forums about using your knee for your Z.
The knee mill is not designed for it, you crank it to your desired height and lock it. That's the way it's intended.
I've never come across a job I couldn't do with 5" or 6" travel in the quill. Some jobs I have 10 tools set up. It's all
in your tool setup. You will need some extended tool holders for your shorter tools.
Unless, of course , you want to bore out your big block Chevy.
The knee mill uses an acme screw and miter gears to move that knee. When you do a peck drill cycle , you are raising havoc on those parts.
You will never get the speed that you get from your quill. Check any knee mill with some use what happens when you unlock the Knee. It will sag.
A bed mill ,where the whole head moves up and down ,has a counter weight,which is usually inside the casting, and runs on ball screws, no miter gears needed.
Wheather you add air cylinders, gas shocks, or whatever, you'll never get the speed, you get from your quill.
Compare the weight of the head on a bed mill to the weight of your knee, with saddle and table, and / or vise and part , all sitting on top an acme screw and miter gears.
I WOULDN'T do it, but , then again, it's your machine. Build it the way you want it.
besides all, Gecko doesn't make a drive big enough for a servo big enough to do it.
Ed V