It is to be remarked, however, that the variation in the diameter of the holes affects these standards, since if the holes are made sufficiently large either gauge would enter, although the axis of the holes and of the pins on the gauge might be the proper distance apart; hence the gauging for length depends to some degree upon the degree of accuracy in gauging for diameter.
Referring now to the construction of the jig, or fixture for drilling the link shown in [Figs. 1701] and [1702]: the base piece is provided with two short hubs, r and s, upon which the link is to sit, and it is obvious that these hubs must be faced off true with the bottom face of the base, while the link must also be faced so that it will be level, and not be bent or sprung when clamped by the screws e f. It is obvious that the hubs r and s may be omitted, and the link be flat on the base plate; but this would not be apt to hold the link so steadily, and greater care would be required to keep the surface clean. It is also obvious that in the form of jig shown there is a tendency of the screws e and f to bend the piece d; but in the case of small pieces, as, say, not exceeding 8 inches long, piece d may be made strong enough to resist the screw pressure without bending. If, however, the link were, say, 18 inches long, it would be preferable to have projections in place of the hubs r, s, and to let these projections extend some distance along each end of the link, using four holding screws, and clamping the piece d on the inside of the hubs h g. To facilitate the rapid insertion and removal of the link into and from the jig cap-piece, d is pivoted on screw f, while a slot v is cut at the other end, so that when the two screws e, f are loosened, the cap-piece d may be swung out of the way without entirely removing it.
Fig. 1704.
Fig. 1705.
