 Often a jig is hardened; for a jig borer this requires the material to be bored first and then hardened, which may introduce distortion.The jig grinder was developed as a machine with the precision of the jig borer, but capable of working materials in their hardened state.Before the jig borer was developed, hole center location had been accomplished either with layout (either quickly-but-imprecisely or painstakingly-and-precisely) or with drill jigs (themselves made with painstaking-and-precise layout).