After years of using an adze, scorp, and curved-bottom plane to rough out chair seats, I came up with this router jig to quickly carve a symmetrical hollow for a nearly finished seat.

To make the jig, first equip your plunge router with guide pins made by slipping 2"-long machine screws through steel sleeves (available from home centers). If your router base doesn't already have four tapped holes, drill and tap your own or make a subbase to accommodate them.

Construct the jig base (I used 34 " MDF) to fit snugly around your chair seat blank and form the rail and carriage curves to fit snugly around your—ahem—curves. It might take some trial and error to get them just right. The depth of the curves on my rails ranges from 0" at the end of the arcs to 34 " in the middles.

Space the carriage rails to capture the router guide pins while allowing them to slide freely. Notch the bottom of the carriage so it fits snugly over the base rails but still moves front to back.

Clamp the jig base to your workbench; then double-faced-tape the seat blank in the jig, centering it on the arcs. Chuck a 12 " straight bit in your router. Then, nibbling away about 316 " in a pass, run the router side to side on the upper carriage rails. After one pass, slide the upper carriage forward for the next. It takes about 30 passes to cover the entire seat. Then lower the bit another 316 " for the next round of passes, and continue until you reach the desired depth.

The router does most of the rough sculpting work for me. All that remains is a little fine-tuning with a scraper or a power sander.
—Bob Hockema, West Lafayette, Ind.