I want to make a printing fram about 24' x 36". I have made an 8x10 and a 12x18, with the usual split back, but my concern is the pressure spring, I used old band saw blades. For this I will need something a little more robust I think. I saw something a long time ago in an old photo showing a large printing frame that used what looked like wooden wedges and strips of wood to hold the back inplace. any suggestions?