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 to the exact size and shape required in a large slotting machine. All the machines in the frame shop are very large, the bed of the slotting machine being at least 50 ft. long, and the machine has three or four tools working at once. Eight or ten frames are placed one on top of the other, and all are slotted together at one operation, the top frame only having been marked off, and the proper outline drawn upon it. The next operation is to mark off and drill all the bolt and rivet holes, of which there will be from 300 to 400 according to the size and type of engine. The holes for bolts and cold rivets are drilled ¹⁄₁₆ in. less than the finished diameter, so that they can be reamered or “rose-bitted” out by the erectors when fitting up the cylinders, stays, and brackets to them. About four or five frames are drilled together in one batch, of which the top one is