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side go to driven pulley and pass over it, that is, assuming the driving pulley parts with the belt beneath it.

Crossed belts are frequently used side by side, with "open," i.e. not crossed, belts, to reverse the direction of rotation of counter shafts to lathes and screwing machines when engaged in using dies or taps.

There are two distinct sets of pulleys required on the countershaft when the reversing motion is to be faster than the other one; this is obtained by pulleys of different diameters. When the speed of rotation is to be the same in both directions, three pulleys only are required, the two outer ones carry the open and crossed belts respectively, and are called idle or loose pulleys. The counter shaft can be instantly thrown into action by transferring one or other of the belts to the fast pulley between them.

Referring to the foregoing it will be understood that the belt forks are in opposite directions; these are to guide the belt on to the fast

FIG. 448A."Blackwall" hitch.

pulleys as required. Another way of doing this is to employ two pulleys with a clutch between them. The clutch actuates a cone disc which has its counterpart in the internal part of the pulley's rim. This is a very effective and smooth form of drive, there being no belt forks required.

Transmitting Motion by Belts.-Fig. 440 shows the method of driving by belt a shaft placed at an angle. The two idle pulleys being placed on a shaft at right angles to the driving and driven shafts. When two parallel shafts lying in the same plane are too close for a direct drive, the arrangement shown in Fig. 441 is found satisfactory, called a Quarter Twist return belt.

Figs. 442 and 443 show two forms of tapering cones for altering the relative speeds of the driving and the driven. shafts. These pulleys allow of a minute and continual change of the speed by traversing the belt.

The stepped speed cone shown in Fig. 444 may be considered as a modification of these taper cones.

"Slinging" a Piece of Work.-In fixing a rope sling on the hook of a crane or pulley block a secure way is to first twist a loop in the rope, as shown in Fig. 448A; the more pull there is on the rope, the tighter the loop grips the hook. This method is an improvement on the single loop, especially when the work has to be carried for a distance, high above the machinery in the shop. For the above purpose two slings are better than one; and by first placing a piece of canvas on the bright parts the possibility of the work slipping is diminished. Bright shafts are carried more securely by two slings than by one; the slings should be of an equal length. Rope slings are more reliable than iron chains. The former show fracture some time before severance, while the latter break without warning; this defect is greatly overcome by using a suitably strong chain, and further by periodically annealing every link.

Tackle for lifting and shifting Material.-One of the most important factors in the economic working of an engineering workshop is the facility with which the various iron castings and forgings are moved

from place to place, or to the machine tools. In modern and wellequipped shops one or two travelling cranes, worked either electrically, or by steam, or hand power, run the whole length and breadth of the shop. To such machines which cannot be conveniently reached by the traveller, i.e. those situated beneath the balcony, provision is made by having a single rail (with junctions and side tracks as required), upon which trolleys carrying pulley-blocks are located. There is by this arrangement a complete service of blocks always ready to the workmen's hands, so that waiting for a crane or a "lift" is not known. This is decidedly an advantage. We have seen men frequently wait for the crane and pulley-blocks too from ten to thirty minutes, and while they were being served others had to wait.

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Figs. 445, 446, show material being run from the stores to the shops for either machining or fitting there.

Fig. 447 shows a view of a modern machine shop fitted complete with Herbert Morris and Bastert's system of Overhead Runways. The lifting gears and trolleys in this picture are engaged in taking material to and fixing same in the various machines it has to be operated on.

Fig. 448 shows this system being used for shifting a radial drilling machine from one place to another. Loads with this system are travelled with marvellous ease. The trolleys run on ball-bearings, and, owing to the high-class manner in which they are made, it is practically impossible for them to get out of order.

CHAPTER XIX.

METHODS OF WORKING.

THERE are three distinct systems of working in this country. The first may be called "time work," where each operative is paid at a predetermined rate of wage per hour according to the agreement made when engaged either by the principal manager or the foreman, as the case may be. The amount may be the "standard rate," or less or more, according to personal ability or merit. In many establishments each order has a working number, and all work for that particular order is booked daily by every operative engaged on it. From this the actual cost of production may be ascertained, and for similar work comparison can be made from time to time.

In such establishments as make machines to a standard pattern a closer application of the "time system" is frequently observed. The quantity of pieces are given out to be "machined," and a record is made. of the fact, and the time is also noted, both then and after the completion of the work, so that by a daily perusal of the storekeeper's book by the manager or foreman the eye soon becomes familiar; and since each operative is engaged usually in his special work, any great difference in the time booked is quickly detected, and inquiries are made. These investigations are very helpful to the managing staff, inasmuch as they make it familiar with all the reasons for delay or improvement, as the case may be. It is a wonderful and orderly system, because by it the exact stage of the work in progress can be ascertained not only to a day but to an hour.

Another system is that of piece work. One of the first essentials of a successful piece-work system is the establishment of a proper method of arriving at piece-work prices. The usual method pursued hitherto when prices have to be settled for a new machine is to either guess at the price from the nearest parallel case in the cost-book, or else to put one machine through the shop on "time work," and take the piece-work prices from the booked cost of the time work. Both these methods are inaccurate and unsatisfactory, especially the latter, for in this a distinct temptation is held out to the men to make the time job last as long as possible so as to get high piece-work prices, after which they take care to do the piece work itself at a slow rate, only making such profit as will not result in the price being "cut."

A more satisfactory system is that in which the price of each process is obtained by tabulating and pricing each of the elementary operations

into which it is sub-divided. To carry this system into effect it is necessary that speed and feed tables should be prepared for all the machine tools and appliances, and that notes should be taken continuously of the time taken on all elementary hand processes, such as the time taken to put the change wheels on a given lathe, the time taken to remove a face plate and put on a chuck, the time taken to remove a given weight from one part of the shop to another, and so on.

A continuous record of these matters taken day by day will not only be useful in settling piece-work prices, but it will also enable the manager to know where time is being wasted and where economy may be effected by improved methods.

The speed and feed tables having been prepared, the calculation of the cutting time of the tools may be effected by very simple formulæ ; and if this were all that is necessary the piece-work prices would be a matter of a very simple calculation, and could be got out by the draughtsman when getting out his list of quantities and weights.

The point of real difficulty is the determination of the idle time; that is to say, the time lost in getting the stuff out of the stores, setting it in the machine, changing tools and chucks and so forth, all of which will take greater or less time according to the efficiency of the management.

The percentage of idle time is a good criterion of managerial ability, for upon it depend to a large extent the commercial success of the

concern.

Before calculating the time which will be taken to do any given job, we must decide upon the cutting speed and rate of feed. These can only be determined either by experiment or from previous experience, as they depend upon many conditions. The job itself may be of such form as to spring or even break under the strain of a heavy cut, or its shape may be such that it cannot be held in the machine with sufficient firmness. The strength and stiffness of the machine tool, the chuck or vice, the slide-rest, and the cutting tool itself must all be considered. Then, again, the speed and feed are governed by the degree of accuracy required.

In jobs requiring no great accuracy a slight spring does not matter, and a heavy cut may be used; but where accuracy is needed, spring is not permissible, and light cuts are essential.

In connection with the following formulæ a few figures as to cutting speeds and feeds are given. These, however, must not be regarded as rigid figures, applicable to all cases, but rather as bases to commence from when experimenting to determine the right speeds for new jobs.

Lathe Work. The number of revolutions per minute for a given cutting speed is obtained by formula No 1 :

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The speed so found will probably not coincide with any of those on

the speed and feed tables, but, of course, the nearest is taken. The time required for each traverse is then found by formula No. 2 :

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L = length of traverse in inches (whether sliding or surfacing.)
F = feed in inches per revolution.

EXAMPLE.-A shaft 2 in. in diameter to have a cut taken along 36 in. of its length.

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Cutting Speeds.-Cast iron, 30 ft. to 36 ft. per minute; steel, 16 ft. to 26 ft.; hardened steel and chilled iron, 13 ft.

Drilling formulæ Nos. 1 and 2 apply to drilling, C being the cutting speed at the periphery of the drill, R being the revolutions per minute of the drill, and I the depth of the hole.

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EXAMPLE.-Hole, in. diameter; 3 through in wrought iron.

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Milling. The speed of the cutter in revolutions per minute for a given cutting speed is given by formula No. 1, in which C = the cutting speed at the periphery of the cutter, and D the diameter of the cutter. In preparing the speed and feed list the feed of the table in inches per minute, with the belt on the different cones, should be taken. The time taken for a given traverse is that given by the formula No. 3 :—

L
T =
F

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