Boring deep holes in metals, especially when the hole is of very small diameter,andit is necessary to have it drilled straight and true, is not always an easy matter. In boring pistol and rifle barrels, for instance, nearly as much time is employed in in removing the drill,clearing,and lubricating it,and replacing the barrel and drill, as in the drilling itself. The drill shown in the accompanying engraving was brought to our notice by Wm. A. Chapin, of White River Junction, Vt., and introduced by him into the U. S. Armory, at Springfield, Mass., and is intended to obviate the difficulties alluded to,and save this otherwise wasted time. The drill is, as seen in Fig. 1, a " pod " drill, milled to crescent form, in transverse section, the milled semicircular score being for the reception of the chips. Throughout its whole length it has a channel, seen in both figures, but more plainly in Fig. 2, that terminates at the cutting end, or point, and near the other end connects with a funnel to receive the oil or alkaline water, which acts as a lubricant. This score is milled or planed in the body of the drill, and covered with a piece of sheet steel, held in place by soft solder. Fig. 2, the enlarged cross section, shows this arrangement. At the cutting end of the drill, the heat, caused by friction, will be greater than at any other point,and if the drill is used horizontally, the oil will be thinned and find its way to the point. If, at any time, the oil passage should become clogged, the hand end may be opened and a wire introduced for its cleansing. This end may be closed by any simple plug that may be readily removed for the purpose. This clogging, however, rarely occurs. Tunneling Street Crossings. Engineering speaking of the proposition to construct either bridge or tunnel crossings on the crowded streets of London, condemns both plans. Arguing against bridges, Engineering says: " We have sufficient experience, from a lengthened'trial of the overhead bridge spanning the most crowded portion of Broadway, New York, that such a system of street crossings j is of but little service; decrepit persons were unable to use it, business people too hurried, ladies were assisted over the street by the police, and the bridge was scarcely employed, save by idlers, while the only one who derived profit from it, till it was removed a few months ago, was a neighboring photographer. And if a bridge has proved itself objectionable in a situation where, of all others, a bridge should have proved itself most beneficial, a subway would be still more useless and objectionable." We certainly cannot see the force of this reasoning. In no single respect, but that of being on a different level from' the street, is a subway like a bridge. But while the bridge must be high enough to allow vehicles and loads of all sort to pass under it, and its ascent and descent is consequently wearisome, the floor of a tunnel need not bo more than eight or nine feet from the upper surface of the roadway. We have yet to hear any valid or even plausible objection to tunneled street crossings.
This article was originally published with the title "Self-Lubricating and Self-Clearing Drill"