After using the Joe's 2006 for some time, I decided I wanted a fourth axis. Since there is limited clearance under the gantry, the rotary axis would need to be outboard of the machine. I had seen a photo of a home-built machine that used a Delta woodworking lathe as the basis for the rotary axis and decided that I would try to do the same.
In order for this to work, I would have to build a new gantry for the router that would allow the carriage to travel beyond the table. Just in case I would want to build an automatic tool changer, I would build it to travel beyond both sides of the table.
I used design elements from several routers I had seen online including the Z-axis from this one. It uses two pieces of 1030 extrusion side-by-side.
Here's mine. I spaced the extrusions two inches apart to make room for the lead screw in between. This keeps it as close to the gantry as possible and gives a wide stance between the bearings that ride on the gantry.
I also used elements of Joe's 4x4 hybrid for the gantry including 2040 extrusion and v-groove bearings.
I was happy with the performance of the Dumpster lead-nuts on the original machine but upgraded to 10 pitch 5-start lead-screws on all axis to get faster rapids.
The gantry legs are MDF with a 3/16 x 1-1/2 inch steel angle stiffener bolted on. The angle also allows a place to attach the horizontal extruded beam. The lower torsion box is stock Joe 2006 but the sides have been redesigned. They are shorter and have a notch for the extrusion to rest in. They retain the use of the original skate bearings on aluminum angle.
Up and running!