On Quilters Cache is a pattern for a 24" carpenter's wheel. Each square or hst is 3" finished. If you follow the directions but make each square 2" finished, then you will have a 16 1/2" carpenters wheel(unfinished). I would add a 2 3/4" x 16 1/2" strip to top and bottom, and a 21" x 14 1/4" strip to each side. This will give you a panel of 21" x 28". If you make the wheel the size of the panel, parts of it will be lost in the curve of the pillow top and bottom. The site is
http://www.quilterscache.com/C/Carpe...heelBlock.html
Good luck!! Ann