even with the truss rod fully loosened my neck wont bow enough. I saw a diagram in a bass book which showed a c-clamp combined with an iron bar (using shims etc to prevent damage to the neck). The notion is that with exerted pressure from the c-clamp the neck will bend before the "iron bar" does. My question is... how much pressure etc is safe to put on the neck? i dont want to crack/break it by cranking the c-clamp too much. is this solution really viable?