Fig. 1482.
Fig. 1483.
It is obvious, however, that we have here tested the alignment in one direction only. But to test in the other direction we may use a pair of straight-edges termed winding strips, applying them as in [Fig. 1479], to test the stem, and as in [Fig. 1480] to test the eye e, and finally placing the winding strip c on the eye of f while strip d remains upon e, as in [Fig. 1480]. The two strips are sighted together by the eye, as is shown in [Fig. 1481], in which s and s′′ are the strips laid upon a connecting rod, their upper edges being level with the eye, hence if they are not in line the eye will readily detect the error. [Fig. 1482] represents an application to a fork ended connecting rod. Pattern-makers let into their winding strips pieces of light-coloured wood as at c, c, c, c, in [Fig. 1483], so that the eye may be assisted in sighting them.
It is obvious that in using winding strips they should be parallel one to the other; thus, for example, the ends a, b, in [Fig. 1481], should be the same distance apart as ends c, d.
If less than three straight-edges or parallel strips are to be trued they must be trued to a surface plate or its equivalent, but if a pair are to be made they should have the side faces made true, and be riveted together so that their edges may be trued together, and equal width may be more easily obtained. For this purpose copper rivets should be used, because they are more readily removable, as well as less likely to strain the work in the riveting.
By riveting the straight-edges together the surface becomes broader and the file operates steadier, while the edges of the straight-edge are left more square. Furthermore parallelism is more easily obtained as one measurement at each end of the batch will test the parallelism instead of having to measure each one separately at each end. If three straight-edges are to be made they may be riveted together and filed as true as may be with the testing conveniences at hand, but they should be finally trued as described for the surface plate.