. Sheet metal workers' manual; a complete, practical instruction book on the sheet metal industry, machinery and tools, and related subjects, including the oxy-acetylen welding and cutting process . dge of the seam in the vessel and aids in bendingthe seam over. Care should be exercised not to depress the upperdouble-seaming roll too hard in the first few revolutionsof the rolls, but allow pressure of the,double seaming rollson the seam to bear gradually. The double seaming machine described will operate onNo. 26 gauge iron and lighter (U. S. Standard). Thelarge machine, having a throat of 15%
. Sheet metal workers' manual; a complete, practical instruction book on the sheet metal industry, machinery and tools, and related subjects, including the oxy-acetylen welding and cutting process . dge of the seam in the vessel and aids in bendingthe seam over. Care should be exercised not to depress the upperdouble-seaming roll too hard in the first few revolutionsof the rolls, but allow pressure of the,double seaming rollson the seam to bear gradually. The double seaming machine described will operate onNo. 26 gauge iron and lighter (U. S. Standard). Thelarge machine, having a throat of 15% inches, will doubleseam work 15% inches deep, 4% inches diameter andlarger. The small machine, with a throat of 10 inches,will double seam work 10 inches deep, 3 inches diameterand larger. Machines of the same type are manufactured for powerdrive and heavy capacity. SHEET METAL WORKING MACHINERY 109 ELBOW MACHINERY In making a pipe elbow the blank is first cut from pat-tern, and if the elbow is to have a lock seam in the throat,the longitudinal edges of the blank are edged prepara-tory to grooving or seam closing on the folding blank with the lock edges is then formed and rolled. Figure 70.—Curved Elbow Shears. into a cylinder with the forming machine, and the corre-sponding edges are locked together and the seam madetight with the grooving machine. In the case of the riv-eted elbow it is held together with rivets. In some shops the elbow blank is cut from pattern withthe hand snip or the bench shears, but in a shop wheremany of the same kind of elbows are manufactured a more 110 SHEET METAL WORKERS MANUAL rapid means of cutting elbow blanks is used, namely, apress and dies, or the curved shears. Curved Elbow Shears.—This machine (Figure 70)resembles the squaring shears (Figure 1) and is oper-ated in the same manner, but in place of having straightcutting blades, curved blades and blocks are fitted. Ac-cording to the blades used the curved shears will cut elbow
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