Imágenes de páginas
PDF
EPUB

ENGINEER'S BOOK OF THE WEEK.

"MACHINE TOOLS AND WORKSHOP PRACTICE."

THIS

HIS useful publication deals with a branch of engineering in which new developments are constantly taking place, and the author may serve the purpose of keeping not only the student, for whose use it is primarily intended, but the busy professional man acquainted with the latest methods of workshop practice. One must keep abreast of new developments, and it is common knowledge that the number of machine tools is rapidly being added to, with a consequent change in manufacturing methods, and sometimes, indeed, a radical departure from old systems.

It is true that in the columns of PAGE'S WEEKLY and other technical publications the improvements which are being effected in grinding and milling, and turret lathe work are being constantly dealt with, yet a text book which cements the information on any one subject is to be warmly welcomed. The main object of the book, as expressed in the title, is to explain the construction and use of machine tools in that connected form which long experience of practical work and teaching has proved to be the most suitable.

The most important chapters in the book are those dealing with measurement, turret lathes, grinding and milling, and these have been illustrated in detail Exact measurement, always of the first importance, is becoming more than ever necessary in modern mechanical workshop practice, owing to the use of interchangeable parts in machine construction. Theoretically, of course absolute accuracy is impossible, and only the close approximation can be obtained, but seeing that the ordinary Whitworth machine measures millimetre, and the electric dimensions and magnitude of

1 4,000

micrometer

of a small

1

the order, 5,000,000 of a millimetre, we have, at least, reached a point in detecting error beyond the capacity of existing machines to correct, and may, therefore, rest content. The author deals with turret lathes in a long and interesting chapter, selecting for notice the Hartness

"Machine Tools and Workshop Practice," by Alfred Parr, with an introduction by William Robinson, M.E., M.Inst.C.E. With 500 illustrations. Longmans, Green and Co. ios. 6d. net.

Flat Die type, the Alfred Herbert Gisholt, Hexagon, the Brass Finishers' and Capstan lathe, and pointing out the advantages of these different machines for varying classes of work. Attention is properly directed, however, to the fact that success in the manufacture of machine tools demanding accuracy depends largely upon methods which will produce better work than the lathe; hence the necessity to finish the work by grinding with emery-wheels in a suitably designed machine. It is obvious, indeed, that the introduction of hardened spindles, bearings, etc., into lathes, milling and other machines, is only made possible by the introduction of suitable grinding machinery, and all engineers realise not only the improvement in the quality and durability of the work thus brought about, but what is of equal, perhaps of even greater importance in these days of strenuous competition, the great saving thus effected in the cost of production. As a matter of experience, some materials, such as soft steel, can be worked to much better advantage by grinding than with the lathe. A satisfactory emery-wheel is a very important factor in the production of good work, but only a good variety of shapes, sizes, and grades of wheels, illustrated in the book, can be trusted to bring out the full possibilities of grinding machinery. The illustration shows a Universal lapping and grinding machine. The principle on which this machine depends in the lapping out of holes in the use of a series of eccentric spindles. The inner one carrying the grinding wheel is somewhat less in diameter than the hole to be ground, and revolves at a high velocity. This grinding wheel is brought into contact with the surface of the hole to be ground by adjusting the orbit (in which it revolves and which orbit revolves) to the necessary extent, which is accomplished by increasing the eccentricity of the spindles by means of the band wheel, shown in the illustration on fig. 8. These movements are combined with an adjustable vertical reciprocating motion of the whole system of spindles, actuated by the crank-rod and levers (figs. 10, 22 and 24), for the purpose of traversing holes of various depths. The eccentric orbit is adjusted centrally with the hole by means of the transverse adjustment on the head stock (fig. 3), and longitudinal

[blocks in formation]

adjustment on the main table (fig. 4), this table having a fine adjustment with worm and wheel (fig. 5) which is actuated by a clutch (fig. 6). The correct position is found by inserting the grinding wheel in the hole and revolving the main spindle (fig. 7). The feed is obtained by carefully measuring the eccentricity of the grinder spindle by turning the hand-wheel (fig. 8) at the top of the main spindle, which is then fixed in position by the lock-nut (fig. 9). The emery-wheel can be raised by lifting the connecting rod (fig. 10).

The milling machine is not, of course, by any means modern, but it was not until comparatively recently, as readers will remember, that it has become universally adopted as an absolute necessity in all branches of

trades.

engine construction and machine building The chapter on this subject is copiously illustrated, and will well repay the reader's study. The remainder of the subject matter is arranged under the head of gearing and gear cutters, filing and erecting, vice-work and tool forging processes, and hydraulic machine tools, and the final chapters deal lucidly with transmission of power and methods of working. A good index adds to the value of the work, the compilation of which must have demanded no little skill in the selection of material. To write a comparatively small book on so large a subject, and yet to have included so much, is a task on which the author may look back with satisfaction.

OUR COLONIAL RAILWAYS.

SIERRA LEONE, LAGOS, AND THE GOLD COAST.

T

HE present position of railway enterprise in British West Africa is summed up in a report drawn up by Messrs. Shelford and Son,* consulting engineers, and included in a return recently presented to Parliament.

An expedition which left England on October 25th, 1893, for the purpose of making a preliminary survey was the first active step taken towards the construction of railways in Sierra Leone. The survey comprised an examination of the route from Freetown via Hastings, Waterloo, Songo Town, Rokelle, to 120 miles from FreeBumban, a distance of some town, the route being that followed by Major Festing during his expedition in 1888 and proposed by him for a railway.

The same party also examined a scheme for a light railway in the Sherbro district from Bonthe to Mina, and thence to Sembahun, near the Liberian frontier.

From the former survey it was evident that a line from Freetown to Songo Town would form a trunk line for all railways in the colony, in whatever direction they might eventually spread over the interior. This portion, 32 miles in length, was accordingly authorised in September, 1895, and construction was commenced in March, 1896. A gauge of 2 ft. 6 in. was adopted for reasons of economy in spanning the numerous ravines traversing the route of the railway.

With regard to extensions from Songo Town, the result of Governor Sir Frederick Cardew's journeys through the colony in the years 1894 and 1895 showed that a more productive country would be tapped by a line to the south of that to Bumban, and upon his recommendations the further surveys of the line were undertaken in an easterly direction via Rotifunk, Mano, Bo, and Baiima, towards the Liberian frontier. The extensions have been since carried out in sections step by step, the route finally selected being that

Since the date of this report, Sir William Shelford, K.C.M.G., has retired from the firm of Shelford and Son, and the business of that firm has been carried out by Sir Benjamin Baker, K.C.B., K.C.M.G., LL.D., F. R.S., D.Sc. (Past President of the Institution of Civil Engineers) and Mr. Frederic Shelford, B Sc., M.Inst.C.E., under the style of "Baker and Shelford."

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small]

A suggestion has been made during the administration of Major Nathan, R.E., that residences for officials should be placed upon the salubrious heights above Freetown instead of in the low, unhealthy town at the foot of the hill, and as a result the construction of this line as a steam adhesive railway was authorised in August, 1902. This important local railway is now completed, the opening having taken place on March 1st, 1904. It starts from the terminal station of the main line in Freetown, and, though the length is not great, the difficulties were considerable, there being a large quantity of excavation in hard syenite and laterite, and much work to be done in the streets of Freetown, which are not well adapted to the laying of a railway. The gauge is the same as that of the Sierra Leone Government Railway, viz., 2 ft. 6 in. The gradients are steep, being 1 in 23 for a large proportion of the route. One of the locomotives, by the Hunslet Engine Company, used on this line, is shown in the illustration on page 295.

[merged small][ocr errors][merged small][merged small]
[subsumed][subsumed][ocr errors][subsumed][subsumed]
[blocks in formation]
[graphic]

be proceeded with.

As a result of this expedition Mr. W. Shelford, M. Inst.C.E., was instructed to carry out during the dry season of 1894-5 a survey for a railway by alternative routes, and a reconnaissance of the following routes was accordingly made: (1) Lagos to Ilaro via Otta; (2) Ilaro to Abeokuta; (2A) Otta to Owowo; (3) Abeokuta to Ibadan; (4) Jebu Ode to Ibadan; (5) Epe to Jebu Ode; (5A) Ejerin to Jebu Ode; (6) Ikorodu to Shagomo. The gauge of railway adopted is that of 3 ft. 6 in., which is in use in South Africa, Australia, and upon the Soudan Military Railway, and can almost be called the Standard Colonial Gauge.

The dates of the authorisation, commencement and completion of the line from Lagos to Otta and subsequent extensions are given below, the railway being constructed via routes I (part), 2, 2, and 3

mentioned above.

[ocr errors]

MAP OF THE SIERRA LEONE TRUNK LINE.

[blocks in formation]

a fcundation added to the difficulties of the work. A road across Iddo Island leads to another shorter bridge stretching from Iddo Island to the main land, thus completing the communication. This is called the Denton Road Bridge," and is 917 ft. in length. The Carter-Denton Road Bridges have no connection with the railway, which was not authorised until December, 1895. They were promoted by Sir Gilbert Carter, former Governor of the Colony, with a view of affording a much-needed means of communication between Lagos Island and Iddo Island, and thence to the main land for foot passengers, horsemen, and vehicles. The need for the Carter and Denton Road Bridges is demonstrated by the fact that an average of no less than 50,000 persons cross between the island and the main land in a single week, of whom as yet but a small percentage continue their journey upon the railway. The public are sometimes inclined to consider the bridges as a part of the railway, and to include their cost in the cost of the railway. This is an error, as the bridges actually compete with the railway to some extent. Communication between the railway terminus and the town of Lagos is established by means of a 2-ft. 6-in. steam tramway which crosses the Carter Bridge and runs to the doors of the traders' stores in Lagos.

THE GOLD COAST.

The construction of a railway from Sekondi to Tarkwa was commenced early in 1898, but owing to cbjections to the selection of Sekondi as the port which were pressed very strongly upon the Governinent, work was suspended until the Secretary of State in July, 1898, held a conference at the Colonial Office with those interested, at which it was decided to adhere to the original proposals, and the actual period occupied in the construction, after the decision that Sekondi was to be the starting point, was 34 months, during which a base with landing jetties, staff quarters, workshops, running sheds, carriage sheds, turntable, etc., was established at Sekondi, a place formerly consisting of a few mud huts, difficult of access, and with no accommodation whatever. This work was carried out in the face of three wet seasons. a prolonged scarcity of labour, and, finally, the Ashanti

[blocks in formation]
[blocks in formation]

JO Miles

tropical showers have

of 4 to 5 in. at a Coast in

ASHIEWE

In some cases fallen to the amount time, and upon the Gold June, 1901, no less than (2 ft. 6 in.) of rain fell in SEKONDI -an amount equal to more average total rainfall of the dom in one year.

30 inches

the month than the United King

GULF OF GUINEA

This has added greatly to the difficulties of construction. At Sierra Leone, owing to the occurrence

« AnteriorContinuar »