Today's progress.

The old machine had a 7" by 7" work area.  The new machine will have 21" by 30", so about ten times as much area in XY plane.  The vertical travel will be greater, too (about 7" vs. 2.5" for the old machine).

Today, I'm cutting a sheet of walnut plywood for the base, then will mount the Y rails and ballscrew.  After that, will carefully keep everything square and add the gantry, which holds the X and Z rails and screws.

Some yet-to-be-resolved issues:

• Need to get new 3-axis controller, as it will just be too much hassle to borrow from the old machine.  Besides, the old machine is still quite useful.
• Need to figure out what kind of motor, chuck, etc., to do the carving.  High torque?  What voltage (steppers are 12V)?  Will probably need a separate power supply.  How to control motor speed?
• Another computer?  Maybe I can have the machines in same room, then use a 15-foot printer cable to drive the big one.  Is 15-foot cable too long for good signal / control?
• Is it time to buy Mach3 software?  So far, my programs have been less than 50 lines of code.  Can go up to 500 with free version of the software, but fully-loaded software has lots more bells and whistles.
• Run to RadioShack to replenish supply of wires, parts for switch box, E-stop switch.  Rail mounts?