In a shop where pipe work is done, and there is no press for bending, or rolls for curving, long lengths of pipes or trough-ing, one of the most useful arrangements to have is a bench fitted up for bending as shown in Fig. 41. The bench must be a fairly strong one, and be rigidly fixed to the wall. Along its front edge should be firmly screwed a bar of stout angle-iron, say 2 1/2 in. or 3 in. Two heavy screw-cramps with large fly-nuts, to fasten to the bench as seen in sketch, will be required. These should be sufficiently long to have two or three holes in the flat part that fits under the bench, so as to be adjustable by drawing in or out.
The sketch shows the bending of a rectangular pipe. A bar of flat iron about 3 in. by 1 1/2 in. is resting on the cramps, and when the sheet is inserted between this and the edge of bench, the cramps are screwed up and the sheet thus firmly held. It is now pulled over, and a sharp edge formed by beating down with a mallet or dresser. Each corner is thus treated in this way, the pipe being then grooved or riveted up. In stronger sheet a batten of wood is sometimes used by drawing along the edge and beating down with a heavy mallet or hammer. This avoids hammer or mallet-marks on the sheet.
In round pipes or half-round gutters it will, of course, be necessary to have a round mandrel to beat the sheet over, and to assist the leverage two battens of timber are nailed together in the form of a cross, and used as in the sketch. Two large eye-bolts are fixed near the edge of bench, and through these a bar or mandrel passed and secured. This bar simply acts as fulcrum, under which the end of the wooden cross is placed, and so enabling pressure to be put upon the edge of sheet.
In heavy work it will make the mandrel more solid to place props under each screw-cramp.
With different-shaped mandrels and some scheming and dodging quite a variety of work can be done on a bench of this description. With a strong bench and a stout mandrel, work up to 1/8 in. plate can be done in this way, and for short lengths up to 3-16 in. thick.
In fixing up a bench of this kind it is advisable to see that no leg is placed in between the two screw-cramps, as in some jobs where it is necessary to bend the plate under the bench a leg would be in the way.