XYZW 4th axis?

[Todd Zuercher]

We have some old Digital Tool routers with 4 axis. X, Y and two Zs (Z and W). We use these machines to do a lot of 2 1/2-D v-groove carving/engraving. Most things we will use both vertical axis simultaniously to double production. I need a way to make the W slave to the Z during a run, but still be independent, for jogging, setting depth, homing ect. In other words read the z command in the g-code file as both a z command and a w command. I would like to have the ability to turn this on and off perhaps with a custom M-code.

I've tried playing with gantrykins some, but I don't think it is going to work for this.

I also need to figure out how to set up Axis for xyzw, or make xyza not think a is rotary.