Summing Z axis on bridgeport

Years back, when I was using Mach, I ran into the same situation. I put a servo on the knee and defined it as a separate axis. I then used custom M6 code to send the tool length offset ONLY to the knee, the quill still handled all the cutting up/down feeds. On toolchange, the knee would lower so that the final move was always up. It worked out extremely well.

If it could be done in Mach, I am sure LCNC can do something similar.

Ok the last two posts are really useful additions & I'm moving along on this now finally although its been awhile (life issues...). I'm tired of cranking the knee manually. I'd like to modify my machine to implement gmouer's method.

I measured the torque to move the knee up and it takes 7nm on my machine with the table laden with the 4th axis spindle and a vice, so I'm going to use a 12nm closed loop stepper, and run it at 3:1 with a 72t htd5 pulley on the end of the knee screw and matching 24t htd pulley on the stepper, with a 133t belt between the two.
On the knee, I was investigating the physical side , and on my interact1 series1 there's a service hatch cover & window behind to enable you to get at the knee crank gear, which is perfect for both replacing the bevel gear which rotates the screw with a pulley, and also for a belt to come out the side of the knee to mount a stepper on there. I think if i unscrew the nut at the top through this, and lock & block up the knee in its highest position, I can crank the screw down enough to put the pulley on without disassembling it all. I will investigate taking the pedestal off and replace the knee elevation screw with a ballscrew.
I read some other comment about the knee on a series1 not being designed to move often etc, so I was surprised to see the machine automatic oiler manifold feeding oil to the knee leadscrew nut and z slideways so I think it could work as a full time axis without wear.