The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

302. is 11%4 to 12!4 pounds per cubic foot. Beech wood is generally impregnated in two stages and will absorb 12% to 22 pounds of oil per cubic foot. It is valuable for marine work, being durable but it cannot be obtained of sufficient length for piles. Its use is confined to planks for covering the projecting portions of piles and for bulwarks, steps and _ slipways.° (Jn- genioren.) Drill for Square Holes Machining comparatively long square holes generally entails a heavy expense, due to the fact that several loca- tions of the work and many cuts are involved before the operation is com- pleted. William R. Robbins, machine- shop superintendent of the Morse Dry Dock & Repair Co., New York, is cred- ited with having devised a tool which will machine square holes in metal in a few hours time. Under the older method of filing and scraping, the same operation has sometimes required sev- eral days. Drills capable of cutting square holes in wood are practicable and have been in use for many years, - but this instance is said to be the in- itial attempt to develop a successful tool FIG. 1--SHAPE OF TOOL FOR CUTTING SQUARE HOLES for machining an accurate square hole in metal, of dimensions which prohibit the work being done on the slotter of on a die sinking machine. A steel casting that was to hold the bottom die of a 100-ton steam hammer for the Morse company's new forge shop was sent to the machine shop to be finished. Two holes, 3 inches square and 7 inches deep were required to hold the die in place. The usual mthod em- ployed in cutting square holes of this character is first to drill them round and then to file and scrape them to the re- quired dimensions. In some instances, a succession of square broaches are used, These are expensive to make, however, and unless the machine shop - 4-throw THE MARINE REVIEW C D : ae A oe FIG. 2--HOW THE LEADER GUIDES THE TOOL happens to have the required sized broaches on hand it would hardly be practicable to make them for one job only. Mr. Robbins used a 3-cornered tool with a chip clearance on each face. The success of the tool lies primarily in the shape and secondly in the manner in which it is used. It does not revolve around a stationary axis as does an | ordinary drill but around a traveling axis which has an elliptical course. The tool works on the principle of a eccentric, its motion being guided by a leader which is strapped in place above the hole to be machined. It is said that the tool makes a clean cut with sharp corners and that holes 6 to 8 inches square are _ easily machined through its use. It will also cut holes as small as %4 inch square. In the tool, the sides of the triangle are equal to the side dimension of the hole to be cut. A bottom view of the tool, illustrating the cutting edges, is shown in Fig. 1. Here, 4 B C is the first cutting edge, C D E the second and & F A the third. The tool is of the end cutting variety. The function of its sides is only to generate the de- sired motion from the leader. With a radial drill there is, naturally, a traverse motion of the head along the cross rail and a radial motion of the cross rail about the column. In cutting square holes with the device under con- sideration, the nut that engages the feed screw on the cross rail is disconnected entirely. 'Thus, it is evident that the tool is free to move as the leader causes it to, because the construction of the radial drill, with the nut mentioned disconnected, readily permits this. An illustration of how the leader ac- tually guides the tool during the cut- ting operation is shown in Fig. 2, A B C D is the square leader and A BE the triangular tool. At first, the side A B of the tool fits closely against the side A B of the leader. B E then moves to the side B C of the leader. The corner EF of the tool moves to the cor- ner C of the leader and the corner 4 of the tool moves to F. This motion is continued from the side A B of the leader to the side B C then to the side C D, to side D A and back to the side A B. The tool makes 14 revolutions to cover the complete outline of the leader. The radial motion of the tool is fyr-: ther illustrated in Fig. 3. The shank of the tool is at A. It revolves 90 degrees upon the circumference of a circle, the radius of which is equal to the distance from the center of the triangle to one of its corners. A moves to B on this circle, then to C then to D and back to A. During this time the cutting edges of the tool are machining away the stock. The fact that the tool js triangular in shape and makes 1% revo- lutions in moving around the complete outline of the leader causes a clean chip to be cut from the piece in process of machining. In setting up the piece for machining, a round hole a little smaller than the required dimension in the finished piece should be drilled. The object of this is to remove superfluous stock. The leader is then strapped in place in the correct location above this hole. It is obvious that the leader should be protected from PEE SES NS ar Se GS en ee FIG. 8--DIAGRAM OF MOTION GENERATED BY THE LEADER undue wear by hardening. In machin- ing pieces where extreme accuracy is fre- quired the leader could be made in sec- tions which would permit the guiding surfaces being finished by grinding. In ordinary work, however, the slight dis- tortion caused by hardening should not materially affect the shape of the leader. This could be further eliminated by making the leader of tool steel and hardening it in cyanide and oil. Are Welding for Ships W. L. Roberts, in the General Elec- tric Review, shows how the anglesmith's work is facilitated by use of arc weld- ing in producing staples, and then pré- June, 1919.