Add a Curved Face on a Tapered Leg
The jig was built with ½” baltic-birch plywood. These particular legs required the curved face have a radius of 1 5/8″. I decided to cut the tenons and the two tapered sides before curving the face of the leg, so the jig had to be designed to accommodate these tenons.
The two guide strips have been clamped in place and the movement of the jig is snug, but smooth, between the strips. Lightly wax bottom of the jig, as well as the table’s surface.
The initial group of passes are completed with the bit 1/16" lower than the finished height, so the final surface is as chip-free as possible.
Ready to Cut
This is the starting position for the very first pass. By pushing the handle ever-so-slightly away from the user at the start of every subsequent pass, the cradle rotates the workpiece into the bit to remove a bit more material.
Make the cradle first
There are only five different parts that make up this entire jig, though you will have to make a matching set of three of those parts. Start by making the cradle base and fasten the two cradle ends at either end. The cradle ends include holes, so the cradle assembly can pivot. This hole is located exactly 1 5/8″ from the middle of the face of the leg which requires the curve. Next, fasten a long piece of plywood, or solid, to the top of the cradle base to create a handle.
The frame assembly
The frame consists of two frame rails, with two frame ends fixing the rails 4 ½” apart. The frame rails are longer than the cradle in order to improve the stability when passing the jig over the router bit. Drill the pivot holes in the frame ends so when the workpiece is secured in the jig the face to be curved is just under ½” above the router table’s surface. With both the pivot holes in the frame ends at the same height, the final curved face will be square to top of the leg. However, if a tapered curve is desired, the far pivot hole could be located a bit lower, perhaps ¼”. This would produce a leg with a curved and tapered face.
The cradle assembly is attached to the frame assembly by two pivot points, allowing the cradle to rotate freely without any play. I used screws for the pivots, but if you intend to use this jig frequently, I would recommend steel rods for longevity.
This jig is designed to pass over a 1/2″ plunge bit on a router table. With the bit extended 1/2″ above the surface of the router table, the resulting curved face on the leg will have a radius of 1 5/8″.
Two straight guide boards are clamped to the router table, centered on the bit. With the jig and router table lightly waxed, the guide boards should be adjusted so the jig glides smoothly, with no slop.
From previous experience I knew that double-sided carpet tape is sufficient to attach the workpiece to the jig’s cradle. I used a number of pieces of tape along its length. When it’s time to remove the wood a great deal of force is required, confirming the strength of the bond.
Rout the curved face
Take a leg (a test leg possibly) and attach it to the jig with tape. My jig has a notch cut into one of the cradle ends. The tenon on the end of the workpiece fits into this notch.
The other end has no alignment device, so I measured to make sure the tapered leg was centered on the jig. Raise the bit 7/16″ above the table’s surface. This first group of passes will take off the bulk of the material. The second group of passes will machine the final surface.
The actual cutting operation is counter-intuitive and requires some slow, thoughtful movements. I suggest some practice moving the jig back and forth along the router table, with the router turned off, until you’re comfortable with the movements. When viewed from above the bit rotates counter-clockwise. The work will pass by the bit to achieve a series of very light climb-cuts. In addition to reducing tear-out, this will also reduce the chance of the bit grabbing the workpiece and pulling it into the bit.
Start with the jig fully to the right of the bit. Grasp the cradle handle and pull it towards you so the leg almost clears the bit. Slide the jig to the left, preparing to feel the bit contacting the work. When the bit contacts, hold the cradle securely and continue the motion until the jig fully clears the rotating bit. Only a small amount of wood is removed with each pass.
After the pass is made, pull the handle a bit closer to yourself so the work is completely clear of the spinning bit. Now return the jig to the right-hand side. No cutting should happen during this movement. You could also remove the jig from the table to return it to the starting position.
Reverse operation midway
Repeat these two motions, right-to-left, then back to the starting position, until half of the face has been machined. The cradle handle will be vertical, and not much wood is being removed per pass at this point. In order to reduce the risk of tear-out, you need to reverse the entire process. Take the jig and place it to the left of the bit. Push the cradle handle away from you, so the leg almost clears the bit. Slowly move the jig to the right and wait for the bit to contact the work. Continue to slide the jig all the way to the right of the bit, while removing a sliver of wood. When you have finished this first pass, move the handle a little further away from you to completely clear the bit, and move the jig back to the left position and repeat. Continue until the entire face is curved. Now raise the bit 1/16″ and repeat the entire process. Keep your hands as far away from the bit as possible during all these motions. A bit of sanding will smooth the curved face.