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Bore Sizing (Ballizing)

A process commonly used for removing slight taper and improving the tolerance of through holes in zinc alloy diecastings. It involves forcing a polished tungsten carbide ball all the way through the hole. No material is removed, giving the advantage of no swarf production. When the section thickness around the hole is not too widely divergent the diameter produced is at least as consistent as could be produced by a reaming operation, but with superior surface finish and the cost is much lower. (Ballizing cannot however improve the straightness or alignment of holes in the way that a reaming operation would.)

Note that the hole diameter produced is slightly smaller than the diameter of the ball. The exact ball diameter required to achieve the target hole diameter depends to some degree on component design and is therefore determined by experiment. Subsequent to the ballizing operation the material around the hole is internally stressed and the diameter will subsequently shrink slightly. The amount and speed of this shrinkage depends on a number of factors, but is not usually problematical unless the maximum size of a mating component is too close to the minimum diameter of the hole.