the four center ribs were timed to final length , 3/8 x 3/8 spruce blocks added to spar to recieve ribs . Mahogony blocks added to end ribs for outer hinge plate . I picked up a 1.5 square steel tube and some line sander paper and made a "line sander" - this worked better than expected . Both sides of stab were line sanded true with little effort. ready for skins.