Assuming that you want the boards flat and the edges square, your gonna need a plainer and a joiner. Find a woodshop. 48" X 13" is a LOT of hardwood to try to sand. Squaring without a joiner is darn near impossible.If you really wanna do it yourself. Delta makes a 13" plainer for about $400 (or less). Good joiners can run as much. If your in the U.S., hit 'www.pricegrabber.com' and look for reconditioned ones. Although most of the plainers I saw were for 12 1/2".