Rebuilt from ground up...

First step was to build a solid steel-framed table.

Next was to level the table after marking location on the floor with red tape.

Then I moved the machine onto double layer of 3/4" plywood and "trued" the three axes.

• Squared the X and Y axes by moving one end of the gantry (with other fastened by one screw).
• Used shims to make Y axes move parallel to the platform (photo below).
• Fastened both ends of gantry to tabletop.

Added stronger 24V power supply and switch and mounted with 3-axis controller on DIN rail.

Moved the computer and monitor.  It is a bit cramped - may move computer to a separate table or stand.  

Finally, added an emergency stop switch.  The switch (left-front corner of tabletop) was a spare from repairing a table saw.  All I have to do is hit it and the motors are disconnected.  The only trouble with this is that the computer thinks the screws are turning, so the zeros need to all be reset every time the E-stop is hit.  Hopefully, I won't need to do that very often.