Steve, are you referring to cracks across the grain on the outside of the bend or longitudinal cracks(checks) in the back at the curve? I have had osage crack across the grain while bending dramatically with dry heat. I use oil on the area I heat and bend and that helps in bends that are not too drastic. I think the oil holds the heat better, helps it penetrate the wood better and prevents scorching. I also use shellac on all newly exposed backs, no matter how well seasoned it is. The shellac is quite stable even when getting the belly very hot and has prevented any checking on the back that is caused by the heating, drying of the wood.