Rural Telecommunications: Hearing Before the Committee on Commerce, Science, and Transportation, United States Senate

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1906 edition. Excerpt: ... sometimes happens that a bar has to be turned, one end of which is pointed. Of course, under such circumstances, the ordinary centre cannot be used, and instead a hollow centre, such as that shown in Fig. 51, must be brought into play, w being the work centred in the dotted hole as shown. It will be observed that part of the shank only is taper to fit the taper hole in the poppet. A ramification of between-centres work may come in, and give rise to the following problem: Suppose we have a long bar or tube, and that on one end of this we have to do some internal work, such as boring it out, and screwing the hole with a screwing-tool. The work is much too long to be operated on by holding it in the chuck, for not only would its weight strain the latter, but it would spring away from the tool. Also its diameter is too big for it to pass through the hole in the mandrel, assuming that the latter is hollow. Now it is obvious that such a piece of work cannot be done unless it is supported at the end which is to be operated uponand that the back centre is useless for this purpose. The problem, therefore, consists in producing something that will support the work without interfering with the tool. In the present instance we will imagine that a piece of iin. tubing, made from No. 18 gauge, is to have an internal thread cut in it. One end is disposed of quickly enough--we simply plug it with wood, and set it in the chuck. With reference to the other end, however, there is only one thing to do, and that is to make a bearing for the work to run in. Having come to this conclusion, we must consider our limitations. The first of these is that there are only two places to which such a bearing can be fastened--the bed and the poppet. But we want room...