A starter pass is not always used, for reasons of minimizing tooling cost when product tolerances are loose and/or it is a short run application, or simply because there are not enough stands on the machine which will be used. In that case, the starting guide is relied upon for accurate and straight entry into the first forming pass. To ensure undisturbed straight entry into the first forming pass, the operator should trim strip corners so that the tip of the strip is fully engaged by the drive diameters before forming begins, as in Fig. 4.9.

Fig. 4.9

A starter pass, as in Fig. 4.10, is helpful in setting up the starting guide as described above, as well as ensuring a good lead into the first forming pass. The rolls are shown split on the centerline for convenience in machining in the case of the bottom roll, and also for ease of modification should the true strip width turn out to be different from the calculated strip width. The developed width for the example shape was found to be 5.386 (page 12). The commercial tolerance for the strip width is .005, so the dimension between the shoulders of the bottom roll is 5.394, assuming tolerance of .001 on roll dimensions. The maximum strip width of 5.392 will fit. Note that if the material is at the maximum of the strip width, the straight length of the wings, nominally .647 (see Fig. 4.15), will change, with one length at...