PROJECTILE-TURNING DEPARTMENT OF THE MIDVALE STEEL COMPANY, PHILADELPHIA, PA.

Eventually, in 1882, they received a contract from the Washington Arsenal for the materials for 15-centimetre guns, one to be hooped with steel wire, the other to be hooped with steel. This gun, the first of 15 centimetre to be constructed entirely of American steel, gave excellent results when tested at Annapolis. It is clear that these materials wrought by a hammer of only nine tons, the most powerful possessed by the Midvale at the time, could not equal the product obtained to-day, but the experiment was a good beginning and persuaded the Company to instal the modern plant necessary for the construction of big guns.

The transformation of the Midvale Con.pany was complete. New Siemens' furnaces of great capacity replaced the old ones, three in number, which, together could only produce ingots of thirty-four tons. A 34-in. Whitworth press replaced the steel hammers.

This press exerting a pressure of 2,500 tons, enabled the Midvale Company to turn out thirty centimetre guns in 1884-1886. The accessories of the press, pumps, cranes, pulleys and shafting, pedestals, anvils, tube expanders, and other forging tools, were similar to those used by Whitworth, now well known at Trubia.

A more powerful press is to be installed at Midvale to facilitate the making of the 30 and 33-centimetre guns. The hardening department, in which oil is used, is well mounted and capable of handling the largest pieces constructed at the present time.

The machine shops are well provided with powerful machines and tools from the best American manufacturers. Midvale does not make use of fluid compression, differing entirely in this respect from the Whitworth process.

They employ excellent first materials in the preparation of the loads for its Siemens' furnaces; the steel destined for the making of guns and armour-piercing projectiles, prepared on an acid bed, necessitates the use of Swedish

ingots or other charcoal pig iron of great purity as regards sulphur and phosphorus. The coke pig irons of Europe and America cannot be employed without risk of bad results. A few years ago, when the Campanil ore was worked in the Bilbao, the Trubia factory used the coke pig irons with good results. Conditions have changed, however, pure ores have decreased in the Bilbao district, and even other Spanish charcoal pig irons are not employed, as, although they possess purity in regard to sulphur, they contain as much phosphorus as coke ingots.

At Midvale the steel ingots are smelted in ordinary metallic moulds, octagonal in shape, with concave faces, and others in refractory moulds, an example followed by some other establishments.

The hardening of the various pieces is done in oil, the furnaces being vertical and fired by gas.

At first it was thought it was not so necessary to take much care in the selection of materials for steel castings as in the case of wrought or rolled. It has been found, however, that phosphorus is equally as prejudicial in a casting as in a wrought or rolled piece, and a limit of o'05 per cent. has been exacted.

The conditions exacted by the American Government regarding steel casting for the army and navy are: the amount of phosphorus must not exceed o'06 per cent., and as regards calorific treatment, that the pieces should be reheated unless ordered to the contrary.

Midvale also manufactures armour-piercing projectiles of chromo-nickel steel, but their tempering process, of the greatest importance in this speciality, is kept secret. They are not limited to the manufacture of gun materials, but construct disappearing carriages for coast defence, having reached a calibre of 30'5 centimetres.

(To be continued.)

, COMBINED BUCKET AND PUMP DREDGER. Messrs. William Simons and Co., Ltd., Renfrew, have just launched, complete with steam up and ready for work, a very powerful dredging vessel of their latest design. The boat is named the Murikiku, and she has been built to the order of the Agent General for New Zealand. Besides being fitted with a special set of buckets for dredging rocky ground, the vessel is fitted with a sand-suction pump. The buckets as well as the suction pipe are made to dredge to a depth of 40 ft. The hopper is arranged in such a manner that the dredgings can be relifted from the hopper and discharged over the side by a special patent arrangement of the builders, and delivered ashore through a long line of floating pipe for land reclamation, or into barges moored at the side of the dredger. Ordinary hinged doors are also fitted to the vessel's own hopper, so that the material can be deposited at sea when required. The machinery consists of two sets of triple-expansion engines and two cylindrical boilers of 160 lb. working pressure.

A STEAMER FOR CUBA.

The new steel screw steamer Regina left Messrs. Workman, Clark and Co., Ltd., fitting out basin at Milewater Wharf, Belfast, last week, for a trial cruise in the Belfast Lough, prior to her departure for Havana. The Regina has been built and engined by Messrs. Workman, Clark and Co., Ltd., to the order of Messrs. R. 1ruffin and Co., of Havana, and is designed to carry molasses in bulk between ports on the Cuban coast and the States. The propelling machinery, which has been constructed by the builders at their engine works, consists of a set of tripleexpansion engines with all necessary auxiliaries, supplied with steam by two cylindrical multitubular boilers.

THE CLYDE.

There was launched on the 21st ult. from the yard of Messrs. Murdoch and Murray, Port-Glasgow, a steel awning decked twin-screw steamer for cargo and passenger service on the River Amazon. On leaving the ways the vessel was named Barao de Cameta, and was taken in tow to James Watt Dock, Greenock, where she will be fitted by Messrs. J. G. Kincaid and Co., with compound engines. This is the fourth steamer built by this firm this year for the Amazon.

WEST HARTLEPOOL.

On the 22nd ult, Messrs. William Gray and Co., Ltd., launched the steel screw steamer Jethou, for She Messrs. A. N. Hansen and Co., Copenhagen. will take the highest class in Lloyd's and Norske Veritas, and is of the following dimensions, length overall 381 ft. 6 in., breadth 50 ft., depth, 28 ft. 4 in. with long bridge, poop, and topgallant fore-castle. Triple-expansion engines are being supplied by the Central Marine Engine Works of the builders, having cylinders 26 in., 42 in. and 70 in. diameter, with a piston stroke of 45 in,. and two large steel boilers for a working pressure of 80 lb. per square inch.

SELBY,

There was launched from the shipyard of Messrs. Cochrane and Sons, shipbuilders, Selby, on Saturday, the 24th ult. a handsomely modelled steel screw trawler, the principal dimensions being 120 ft. by 22 ft. by 13 ft. The vesel has been built to the order of Mr. H. P. Aspeslagh, of Ostend, Belgium, and will be fitted with powerful triple-expansion engines by Messrs. Charles D. Holmes and Co., of Hull. She is fitted with all the latest improvements for this class of vessel.

THE HUMBER,

Earle's Shipbuilding and Engineering Co., Ltd., of Hull, launched on December 30th, the Lucy, a handsomely modelled steam trawler, built to the order of Messrs. Moodys and Kelly, Grimsby, for the Fleetwood Steam Fishing Company, Ltd. Her dimensions are 126 ft. 8in. by 22 ft. by 12 ft. 10 in. moulded, and she will be fitted with triple-expansion engines, having cylinders 12 in., 22 in. and 36 in. diameter by 24 in. stroke, supplied with steam from a large steel boiler working at 180 lb. per square inch.

Dockyard Coal-Handling Plant.

Graham, Morton and Co., Ltd., of Leeds, have obtained the contract for the supply, delivery, and erection at the electrical generating station at His Majesty's Dockyard, Devonport, of a complete coal-handling plant, including coal bunkers, stanchions, girders, flue, and coal measuring and weighing apparatus, and all accessories. All materials used are to be of British manufacture throughout, of the best of their respective kinds and workmanship.

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obtaining it. Thus, a polyhedron is obtained. by a series of distinct operations; in practice the error permissible is gradually reduced, and is amply compensated for by the increase in the facilities afforded. In drilling a hole, a cylindrical surface has to be obtained in a single operation, and so is without the aid of any equivalent process for eliminating the error, or any increased control over the casting. In turning, a little surplus material obviates the degree of accuracy in much the same way, but the minute accuracy to which the slide-rest works to the line round which the material revolves, results in the production of accurate work. In this case, also, a cylindrical surface is required, but it is procured by slow degrees, the dimensions required being attained gradually. During the latter stages, a perfectly satisfactory surface to work to is available and the cylindrical surface bears a uniform ratio to that which has to be obtained; or, in other words, the error is first reduced to a uniform one, it then being a comparatively easy matter to deal with the latter. Rimering a hole is analogous to this, but only in exceptional cases do circumstances permit of this being done. Admitted that there are some methods of rectifying errors made in drilling holes, they at the best of times only effect a compromise. Accuracy is really only attainable by the drilling machine performing the work correctly in a single operation; so, compared with the other machine tools, it is handicapped to a greater extent than one has been accustomed to think. SPECIAL DIFFICULTIES.

HE disadvantages under which a drilling machine performs the work allotted to it, as compared to the other machine tools, are often overlooked. Usually, the latter are machining on "the working parts" of the plants they deal with; these parts are machined on all sides, so their ultimate shape is quite independent of the character of the casting. In these a certain amount of surplus material was provided, so as to permit of some flexibility in marking-off and machining the initial surface. The surface thus obtained is available as a groundwork for all subsequent marking-off and machining; when chosen with discretion it leaves little difficulty for obtaining the other dimensions of the casting to the required degree of accuracy. Thus, unless the casting be an awkward one, there is little excuse for being at fault in obtaining the initial surface, and once this is available, the remainder of the work is greatly facilitated. Very often the drilling of a hole is analogous to performing the second stages of the machining to the same degree of accuracy as before, without the aid of a finished groundwork; this is especially so when holes are required in castings upon which little machining has been done. Working with other machine tools, one can often trace the course the tools will take throughout its travel, the object being to obtain a surface of which one can outline, say, two or three sides; in place of this, how often, when drilling a hole one has to work to a mere centre.

The second surface of a casting must be machined accurately to the first, the third equally so to the first and second, and the fourth to the first, and either the second or third surface. The greater degree of accuracy that is required, the better are the facilities for

To drill a hole is one of the easiest operations a mechanic has to perform, yet it occasionally calls for the exertion of much ingenuity and care. This happens when the hole must occupy a well-defined position throughout its ength with one, two, or, perhaps, three, sides

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of the material in which it is drilled, especially when the latter affords no satisfactory surface to work to. The most obvious expedient is to work to a standard set of templates, as is adopted to some extent in all works. It is not easy to explain why this cannot be followed to a greater extent than is found possible; there are always some well-founded reasons for doing so, not apparent at first sight. Sometimes a modus operandi is discovered that diminishes the difficulties considerably; usually an undue amount of time is wasted before a satisfactory one is arrived at. Some of the precautions adopted and arrangements found convenient when difficulties of this kind are encountered should be welcome. Those dealt with in this article may be modified in various ways, as suggested by each one's experience, or for the special requirements of the work upon which they are engaged.

A RELIABLE DRILL-GAUGE.

A reliable drill-gauge is a great help, and of these there are many on the market; mechanics usua ly prefer those having only the range of holes met with in their particular work, for which reason many make a gauge for their own use, drilling a few holes now and then when a suitable opportunity offers. That shown in fig. I will be found of special service to brass

When working with B.A. screws in brass, the drills for tapping one size of hole can be conveniently used as a clearance drill for the next smaller size. So 5 B.A. tapping is just the right size for 7 B.A. clearance; working in iron, the 7 B.A. clearance is a shade too small for 5 B.A. tapping, the iron being more brittle, the tap should only be allowed to remove as little surplus material as possible. Working with iron matters must be cut much finer; brass-finishers now and then overlook this point, and broken taps are the result.

DRILLING SMALL CASTINGS.

Holes are sometimes required to be drilled and tapped in the centre of circular pieces of metal, the latter are often placed in the chuck of a lathe and the drill fed with the back-centre; the centre of the back of this drill is grooved out, as shown in fig. 2. Owing to constant

FIG. 2.

pressure, the centre of the groove will run out ; to prevent this a smaller hole is drilled, say

in. deeper; this is sufficient to guide the centre when the groove wears.

Many small castings are required to be drilled between centres, and yet it is not found expedient to work in a lathe. A centre, as shown in fig. 3 screwed on to a drilling machine, is of great service for such work. A pair of washers are provided to facilitate the setting of the centre in line with the drill; in the majority of shops this

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FIG. 3.

plan of working between centres in a drilling machine seems never to have suggested itself. It is surprising how easy this simple device will render awkward jobs.