A Clearly Superior Router Subbase
This reader-submitted router sub-base has several advantages that give it superior flexibility. Its tabbed design lets it pop in and out of a table from the top with ease while preventing the router from spinning in the table. The clear acrylic sub-base gives you an unobstructed view for handheld work.
My shop-made router table has one big advantage over other tables— I don't have to remove the subbase when changing between freehand work and table work. That's because the 1/4" clear acrylic subbase I made for handheld use also sits securely in a 3/8" rabbet 1/4" deep in the router table opening.
Make the base plate 1" larger in diameter than the router base, and add a tab at least 1/2" wider on all sides than the side handles, as shown. (This tab makes it possible to insert the router from above and keeps the router itself from spinning.) When mounting the base plate, be sure to align the tab directly underneath one of the handles. To install the router in the table, drop the uncovered handle through the handle opening, and then spin the router 180° to align the base plate. Secure the router in place with short lengths of rubber hose jammed between the handles and the underside of the table.
— Robert Martin, Picture Butte, Alberta