There are several things you can do to prevent cupping when resawing:
1. Use the largest blade available to you. The wider, thicker, and stiffer the blade is, the less likely it is to cup in the cut.
2. Increase the blade tension. You can safely go a notch or two (or even three) past the indicator marks on the tensioning spring. Some bi-mateal blades will withstand many times the recommended tension for ordinary steel blades. The extra tension keeps the blade taut in the cut and helps prevent cupping.
3. Use skip-tooth blades. When cutting through a thick board (or cutting through the width of a board), each tooth is buried in the cut for a long time, raking the wood and cutting away long slivvers. These slivvers lodge in the gullets between the teeth and then are thrown free when the teeth exit the cut. If the cut is too aggresive or the stock is too thick, the slivvers will pack in the the gullets, press against the sides of the kerf, and slow the blade down in the cut. At this point, the tension is not the same along the length of the blade. It's higher where it exits the cut than where it enters it. In effect, the band saw is feeding the blade into the wood faster than it can pull it out. The blade goes slack in the cut and cups. A skip-tooth blade has wider gullets, more room for slivvers, and is less likely to cup in thick stock.
4. Finally, you can use a
variable-pitch blade. This is a blade that was originally developed for the meat-packing industry, but it works like a champ for resawing. Ordinary blades have evenly-spaced teeth (a consistent pitch) and they beat out a rhythm as they contact the wood upon entering the cut. Because the blade in under tension, the rhythmic pattern of the teeth scraping the wood produces a harmonic in the blade and it begins swinging back and forth. This is the condition you see in a blade right before it cups.
A variable-pitch blade won't create a consistent rhythm, it is less likely that the blade will produce a harmonic vibration, and it rarely enters the requisite precondition for cupping. You can puchase a 5/8" variable-pitch blade for the Shopsmith band saw, see
http://www.shopsmith.com/ownersite/cata ... blades.htm. It's a great blade; I've used it to cut 1/16"-thick veneers from curly cherry and figured maple.
With all good wishes,