<DATA MISSING tif no.16,17>
keep the centre-punch mark to one side (not the inside) of the centre of the bend. Take a heat on the other mark and repeat the procedure (Fig .50). Take care with this second bend to direct the hammer blows correctly on to the bend already made; this will become easy after a little practice. Some slight unwanted bending usually occurs in the legs of the U and across the end, but this can be corrected later (Figs .52, 53, 54 and 55).
Take a heat in the centre of the U and twist the legs out of line with each other. Check again that the ends fit correctly in the hole gauge, correcting with a rasp while the piece is hot or with a file if it is allowed to cool. This will remove any slight increase in diameter caused by hammering on the ends. This final check is important as these ends must fit snugly in the hole gauge; too loose a fit will not allow enough material for the full depth of thread. After slow cooling, these ends are threaded using hand-held die stocks and dies (Fig .51). Reheat the end of the U and twist back to the correct shape, set the sides parallel and gently flatten (Fig. 56).
Extreme care must be taken when working these comers in the bottom swage so that not even the slightest crack is allowed to appear on the inside of the bend. If a crack does occur, it is usually the result of leaving too much metal to be worked into the comer. If the bending heats are restricted close to the mark, a neat, strong comer will result.
This method of working gives bends with a pronounced outside radius but a very small radius inside the bend. Square-section material and some lighter flat sections can be bent to accurate dimensions using this technique. Where bends with a sharp outside comer and a pronounced radius inside the comer are required, other techniques must be adopted. Where U-bolts with pronounced radii inside and outside the comers are intended, the threading can be carried out before bending as no hammering on the ends is required.
