Necessity is the mother of invention and I had a need. I wanted to inlay some wood in a box I was building for my wife. I felt like a router table would make it easier instead of using the portable router. I did a quick inventory and here is what I scrounged around the shop.
Old milk crate
Scrap of 1/8" plywood
Scrap wood 2" x 2"
Scrap 2" X 6"
Dry wall screws
Step 1: Cut out hole in milk crate.
Remove the base of the router. Set router on milk crate side towards the opening. Use masking tape to mark the perimeter of the router. The hole needs to be slightly larger for a clearance fit of the router. Using some sort of cutting tool such as a saber saw cut out the marked area. Check that it fits in the hole easily so you can remove it when you don't want to use your new router table.
Step 2: Cut table top to fit router.
Support router with blocks of wood inside the milk crate. Place the plywood on the milk crate to get an idea where the blade will be located on the table top. Drill a 1/2" hole for the blade to protrude. Using the hole center the base plate removed in the first step as a template. Drill the holes and countersink them to mount the router to the table top.
Step 3: Mount the router to the table top.
Use the base plate screws to mount the router to the table top. The entire unit will stiffen as we add more parts. Cut the scrap boards large enough to stiffen the top and attach the top to the milk crate using drywall screws. Countersink the holes to keep the top of the table smooth. I let the stiffeners extend past the table top as handles to move it and to extend the fence.
Step 4: Attach the top to the milk crate.
Drill pilot holes for the drywall screws at an angle through the milk crate and into the table top stiffeners. Attach the top with the drywall screws.
Step 5: Safety is first.
Cut a block of wood that will allow a spring clamp to depress the trigger. Use a power strip as a remote switch next to the router table. Cut a pusher stick or two for feeding wood whenever near the blade.
Step 6: Finish the details.
Add some parallel lines to the table top for easy fence placement. Clamp a board to the table top for a fence and clamp the milk crate to the table for extra security. Adjust the depth of the blade and make something special for a loved one.