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 :

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 :

when T L

=

time in minutes.

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.

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 L the depth of the hole.

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

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:—

in which F is the feed of the table in inches per minute. (See Brown & Sharpe's Treatise on Milling.)

Planing. As planing machines are set to run at one speed only, the preparation of their speed and feed table is a simple matter.

The time taken for a traverse is given by formula No. 4 :—

in which W = width in inches of the surface; L = the length of the stroke; R = ratio of the quick return; C = cutting speed in feet per minute; F == feed in inches per cut, and x a constant depending on the loss of time at each reversal, and which must be determined by experiment for each machine.

(b) Same job, but with quick return having a ratio of 1 to 4.

T=

0'083 x 73 x 36.25 × (1+1)

20 X 0'0625

Here we see the advantage of the quick return.

X 105 = 230 mins.

driven by a screw with a This offers the advantage stroke, but as the reversal place at exactly the same

Slotting and Shaping.--There are two methods of driving the rams of slotters and shapers. In one the ram is reversing motion similar to that of a planer. of a uniform speed of the tool throughout the is dependent upon momentum, it does not take point at every stroke, so that clearance must be left for the tool at both ends, and this renders this class of machine unsuitable in those cases where the tool has to move within definite limits. For these machines formula No. 4 applies, the same as the planers..

In the other class of slotters and shapers the ram is driven by a crank and connecting rod, a quick return being generally obtained by driving the connecting rod through a link instead of attaching it directly to the crank pin. These machines have cone pulleys, and the stroke of the connecting rod can be varied so that a number of cutting speeds can be obtained. In preparing the speed and feed table the number of revolutions per minute of the crank shaft with the belt on different cones should be taken, and the revolutions per minute required for a given cutting speed and stroke are then found by the formula No. 5 :—

=

=

in which C the cutting speed in feet per minute; L = the stroke in inches; and R the ratio of the quick return. It should be borne in mind that in these machines the cutting speed is not uniform throughout the stroke, so that C represents the average cutting speed.

The time required for a complete traverse is given as before, by the formula No. 4, but omitting the constant x, as there is practically no loss of time at reversal.

In addition to the tools enumerated there are in every shop others of a special or subsidiary nature, the speeds and feeds of which also require to be obtained.

The foregoing formula will enable us to calculate very quickly the actual tooling time on the different jobs, but this is only one item among the number which go to make up the total time of the job.

When a man is given a new piece of work he usually has to go to the stores to fetch it, and when he arrives there a stores man not well acquainted with the work may bring him half a dozen articles before he hits upon the right one; and perhaps the workman may stand neglected at the counter waiting till the storemen finish telling each other fairy-tales before condescending to give him their attention. When he gets back to his machine the work has to be chucked or cramped, the tools set, and measurements taken. The time of none of these things can be determined by calculation, but can be determined by a manager who has full power over the drawing office, works, and stores. He can order the work in such a way that the men do not have to go to the stores for their work, but have it laid beside their machines by the labourers in good time. He can also see that only men are employed in the stores who have been through the shops, and know the names and appearance of all the goods used, and he can also suppress gossip.

A tool room and regular supply of tools to the men, without the necessity of their taking them to be ground or dressed, is a natural accompaniment to piecework. The provision of time-saving chucks, tool-setting arrangements, and measuring instruments lies entirely with the manager. For these reasons the true determination of the piecework rates must lie with the manager and his staff, with whom will also lie the work of recording continuous observations of the time taken on the work as it proceeds.

When preparing the schedule of piecework prices it is desirable to prepare, at the same time, a complete list of the materials, with their weight and cost, so that the total cost of the contemplated work may be obtained, and alterations made if it is found excessive. The particulars should be entered into a book.

Lifting Tackle.-Each machine should have a handy jib or girder, a light-block or compressed-air cylinder to lift the work, so leaving the shop-traveller to have to deal with heavy jobs only.

Boring Mill.-This should have jaws (perfectly self-centering) on the face plate, and a turret to take the tools so as to save time in tool changing.

Lathe. In order to save time in tool changing this should have