by operating on stock bars with high-speed milling cutters, and one example, among many, may be cited: Hexagon nuts for 3⅜ in. diameter bolts are made from rolled bars, the cutting speed of milling being 150 ft. per min., giving a production of 90 nuts per day, against 30 formerly. More than 90 nuts could have been produced had the machine been more powerful.
Rapid cutting with planing tools has also developed extensively, the old cutting speeds of 15 to 25 ft. per min. being now replaced by those of 50 to 60 ft. per min., and in some cases even as high as 80 ft. per min., and for the same reasons, as already described in lathe turning, the power absorbed does not increase in anything like the same proportion to the extra amount of work done, so that the wear and tear on the machine is not materially increased.
It was for some time not thought possible to plane at such high speeds on account of the tools coming into contact suddenly with the job and running risks of snapping off through shock, but where high-speed steel of proper quality is used this difficulty is overcome, and a good example or two of rapid planing may be quoted. Using a 7-ft. planing machine with two tools operating on forged steel of medium quality, the cutting speed, depth of cut and feed of each tool is respectively 54 ft., one-fourth inch, and one eighth inch, the speed of reverse being 160 ft. per min.
Another striking example of high-speed planing on a large cast-iron turbine body was: Cutting speed 36 ft. per min., depth of cut 1.25 in., and feed 7 cuts per in., the tool cutting for 10 hrs. without necessitating grinding. Two tools were cutting, each taking a cut as described, the size of the planer being 14 ft. × 14 ft. × 30 ft.
The question of cutting angles for tools is an important one, and the author would advise all interested to peruse the paper written by Professor Nicolson, of Manchester, and read before the Institution of Mechanical Engineers at Chicago this year, and in which he states that the best cutting angle as deduced from the results of experiments is 75 deg. for steel and 80 deg. for cast iron. Of course these angles may with advantage be modified according to circumstances and the nature of any particular class of work.
Objections have been made against high speed steel on the ground of its being brittle; but this is not the case where the steel has been properly annealed and the hardening confined to the cutting area, and sufficient support given to the tools when fixed in the machine.
An example of the great pressure-resisting powers of high-speed steel may be given.
When cutting forged steel of about 30 tons per sq. in. tensile strength and offering a resistance to cutting of about 100 tons per sq. in., a tool of 1¼ sq. in. section was used, taking a cut of seven-eighths inch in depth by one-fourth inch feed per revolution, equivalent to an area of metal under cut of 0.21875 sq. in., the cutting speed being 90 ft. per min., and removing 60¾ lbs. of metal per min., or the enormous weight of 4,010 lbs. per hr. The tool in this instance was projecting a distance of 1⅛ in. beyond the rest (see Fig. 4), and a calculation shows the stress on the tool to be as high as 78.5 tons per sq. in. In another case, cutting forged steel of 35 tons tensile strength and offering a resistance to cutting of 115 tons per sq. in., a 1¼-in. square tool being used, the diameter of forging was reduced by 1 in., equal to one-half inch depth of cut, while the tool advanced three-eighths inch every revolution, the cutting speed being 25 ft. per min. and removing 14¼ lbs. of metal per min. With the point of the tool projecting three-fourths inch beyond the rest, the tool successfully withstood a stress of 51.6 tons per sq. in. (See Fig. 5.)
Although in actual practice tools of much greater section would be used, the results clearly show that, if proper care be taken, tools of high-speed steel are quite capable of withstanding any pressure likely to be met in ordinary workshop practice.
A most important point to observe when taking heavy cuts is that of having the tools quite flat on the bottom side and supported as near as possible up to the extreme edge, as by so doing the pressures tending to break the tool are very considerably reduced. For example, the position of the tool as placed in the rest shown in Fig. 4 would cause a stress of something like 78.5 tons per sq. in. to be thrown on it, whereas when the overhang is reduced to one-half of the original distance, equal to nine-sixteenths inch, the stress is lowered to 14.27 tons per sq. in., a reduction of 80 per cent.
Perhaps one of the most unlooked-for developments in the use of high-speed steel has been the manufacture from it of twist drills, and it would be safe to say that in no other sphere has the new steel justified itself to a greater extent than in the operations of drilling and boring, as its powers in that respect have revolutionized completely modern workshop practice. It is now possible in many cases to drill holes through stacks of thin steel plates as quickly and economically as by punching them, thus avoiding the consequent liability to distress the material due to punching action.
The plates of torpedo and other boats, which are comparatively thin and of high tensile strength, can now be drilled in stacks with such facility that it is no longer necessary to punch the holes, whilst in many articles where it was formerly the practice to core in the holes, as, for example, in cylinder and other covers, or pipe flanges, etc., it is now cheaper and quicker to use high-speed steel and drill the holes out of the solid.
A considerable amount of doubt has been thrown from time to time on the inability to take finishing cuts with high-speed steel, and in the early stages of its development this contention was to a large extent justified, but experience and practice have brought the steel into line and rendered it possible to obtain an excellent finish at high speeds with tools suitably formed and properly arranged in the machines. Some very good examples of finished bright work at high speeds have been made mostly in semi-automatic machines, high-speed steel being used and one cut only taken, the surface finish being most excellent.
This finishing quality of high-speed steel is especially advantageous for tools used in automatic and capstan lathes, because it enables the work to be produced so very much more rapidly; and also, on account of the great resistance of the steel to wearing action, greater accuracy is insured.
As regards the quality of retaining a sharp edge, high-speed steel makes excellent razors, and will long retain without sharpening an extremely keen cutting edge. The author may add that it is thus now possible to those whose time is precious to indulge even in “high-speed shaving.”
The author hopes that the few facts he has given as to the use and development of high-speed steel may indicate some of its uses and progress, but he can scarcely refrain from remarking that many are saying. and rightly so, “Yes! these results are very remarkable; but what of the machines to perform such prodigious work?” and this leads him to speak before concluding as to how one important development often leads up to another of even greater magnitude, and that is in this case the complete revolution in the design of machine tools to cope with the extraordinary increased cutting powers of the latest rapid cutting steels.
It is impossible that the design of machine tools can remain on the old lines, since the difference between them and the cutting powers of the steel is so abnormal, and a sphere of immense area for the redesigning of machine tools is opened out to the ingenuity of the world’s engineers.
That much has been already done is admitted, but the work is naturally of such a nature that only time and experience will accomplish, gradually enabling as nearly as possible the relative powers of the steel and machines to be equated.
In the machine tool department of the author’s firm, this branch of the subject of remodeling their tools has received the closest attention, and a type of their modern 18-in. center lathe for high-speed cutting may be mentioned. It is capable of exerting 65 h.p. equivalent to a belt width of 12 in., and with the aid of a variable speed motor a range of cutting speeds from 16 to 400 ft. per min. is possible, this comparing with an old-type 18-in. lathe having a belt of 4-in. width, and capable of exerting only about 12 h.p.
In a similar way the old types of planing, milling, drilling machines, etc., are all more or less obsolete, and new designs are already constructed to cope with work at speeds and feeds described in this paper.
It is indeed a pleasure to see the new type of machine tool operating with high-speed steel, and treating the work it has to turn out in such a businesslike way, throwing off shavings from steel and iron as one usually sees in turning wood, and imparting a life and energy to the whole establishment in remarkable contrast to the sleepy rate at which metals used to be turned and machined for so many years past, thus exerting an influence on everybody therein to get “a hustle” on that is positively exhilarating in its effects.
Automatic Block Signals in Europe.
The report made by Mr. C. H. Platt for the International Railway Congress on automatic block signals was noted in the Railroad Gazette of Nov. 11, 1904. The report on this subject for all countries except America is by Mr. Margot, of the Paris-Lyons-Mediterranean, and it is printed in the last number of the Bulletin of the Congress, page 1613. In 1899 the P.-L.-M. had 24 miles equipped with automatic signals; since then, automatics have been erected on the Midi, of France, 26 miles; on the London & South Western, six miles; on the North Eastern of England, 10 miles; and on the Austrian Southern, nine miles. Comparing this short list (74 miles, including 26 miles additional on the P.-L.-M.) with the automatic signaling of America, the reporter devotes his chief attention to the question why other countries do not follow the American example.
Discussing experience in Europe, Mr. Margot finds that the locomotive runners accommodate themselves readily to the Hall enclosed disks. There has been no trouble as yet from the accumulation of snow or frost on the glass windows of the signal cases. Answering criticisms which were made at the 1900 Congress, he says that wooden fish-plates have done well on the Midi, and that “the track circuit is no obstacle to the construction of very solid track.” The Hall signals on the P.-L.-M. were installed in 1898, but not for two years did they trust them. Finally, in August, 1900, the old manual signals were put out of service, and the automatics allowed to serve. For the first 16 months there were 365 non-dangerous failures and 17 dangerous; but the similar and
