A good method of levelling thin metal plates, such as No. 20 wire gauge, is the following. In the illustration the plate to be set is " loose " at A B C D; to make it flat, the parts of the sheet opposite the buckled edge must be stretched with a setting hammer, used upon a large circular iron slab, known as a setter. The dotted lines upon the diagram indicate the places at which the blows are to be delivered, and a few additional blows along the centre after the buckles are drawn out will stiffen the sheet. Buckling in sheets of metal is due to impurities in the metal, to a defect in the rollers, or to unequal annealing.

Levelling Thin Metal Plates.