Thought I'd share this cool way to build your own radius-sanding blocks. This is a 12" radius block. First, use a piece of MDF or plywood (whatever you have) and attach your router to one end. Mine is just as wide as the router and about 22" long. Then from the center of the router bit, mark the length of each radii you want to make. I marked my board at 9.5", 10", 12", 14", 16" and 20" so I can use this same board to make all these different radius-sanding blocks. Then drilled a 1/4" hole at each length. Make sure these holes are in the center of the board. Next take another piece of MDF and cut it to the width you want the sanding block to be, mine is 2-3/4" wide (StewMac sanding block width). Then mark the center line of the board and lines equal distance apart. Mine were 3" apart. Depending on how thick your MDF is will determine how many pieces you need to cut to make your sanding block. If you want an 8" sanding block and you're using 3/4" MDF, you'll need the board to be at least long enough to cut 11 pieces plus an extra 15". So for the 8" sanding block you'd want to start with a piece 2-3/4" wide and 48" long. Drill 1/4" holes at each of the 3" lengths starting 15" back from the edge of the board. Drill as many holes as pieces you going to cut plus an extra 5. I used a 1/4" straight cut bit in the router. Bolt the two pieces together at the 12" mark and make your first cut. Then unbolt it and move to the next hole to cut off another piece. So the bolt doesn't come loose as you pivot the router, I tighten two nuts against each other. After your pieces are cut, use double stick tape, line them up and stick them together. Then cut the block in half. Hang on to the piece you cut off w/ the convex radii...you'll use that later. Take the piece with the concave radii and glue it to a backing board. I used a piece of 1/4" MDF.