CHAPTER IX.

ARRANGEMENT OF SHAFTING AND GEARING.

IN the economical management of a manufactory the proper construction and arrangement of the shafting which transmits the power from the motor to the various machines is a matter of great importance.

We are afraid the construction of shafting does not receive the attention it deserves in this country; this is in striking contrast to American practice, which has worked out and brought it to a considerable degree of perfection.

First, as regards the speed and size of shafting best suited for saw-mill work, or manufactories in which the machines run at a high speed; to avoid numerous countershafts or the putting of driving pulleys of very small diameter on the various machines, it is necessary to run the main shaft at a moderately high rate of speed: we think in a mill for general purposes the first main shaft should make 250 revolutions per minute. If a second or third shaft be used to give motion to lighter machines, this speed may be increased with advantage to 300 revolutions per minute, but not above, as a general rule. In manufactories in which the machines run at a moderate rate the shafting is usually speeded at from 100 to 150 revolutions per minute. The whole of the shafting should be accurately turned to gauge, and fitted in bearings having both vertical and lateral adjustment, and provided with efficient means of lubrication. It will be found a

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very poor economy to employ unturned black shafting; in fact, we think it the reverse of economical. For shafts of small diameter, at any rate, we strongly recommend the use of Bessemer steel; in fact, if a slightly increased cost is not an object, the whole mill would be better fitted with them. As steel shafts are stiffer in work than iron, they may be made of somewhat less diameter for the same duty; they will also, if sound, be found to run with somewhat less friction than iron, which in the quality usually employed for shafting is often seamy and unsound. Line shafting is subjected to considerable torsional and bending strains, more especially, however, in saw-mills, where the speed, number of pulleys, and belt tension are excessive. This should be borne in mind when calculating the diameter of the shafting, and the centres to which the bearings are to be fixed. A useful rule for finding the diameter of a wrought-iron shaft, capable of transmitting a given horsepower, may be stated as follows:-Multiply the given horse-power by 125, and divide the product by the number of revolutions per minute, the cube root of the quotient will be the diameter in inches. For saw-mill shafting an increase in diameter of say 15 per cent. on the result thus obtained should be added.

Hollow shafting has not, we believe, been much used for saw-mill purposes, but, as it possesses strength and lightness in a marked degree, we purpose shortly giving it a trial.

In arranging shafting in a large mill, the first length which receives the power from the prime mover should be of greater diameter than the remainder, and the bearings placed closer together, say, 5 or 6 feet apart, whilst 8 or 9 feet apart on the ordinary shaft will be sufficient. In the case of very large power, a bearing should be placed on either side of the pulley, receiving the power from the engine. As regards the increase in the diameter of the

first driving shaft over the following shaft it is difficult to lay down any arbitrary rule, but if it is made about oneseventh larger it will generally be found sufficient, or say a shaft having a diameter of one-fourth the width of the main driving belt will be amply sufficient to receive all the power transmitted. In calculating the diameter of a

shaft it will be found much better to err on the side of strength, as, should a shaft bend or spring in working, the money lost in stoppages, lining up, &c., would in a very short period pay for the difference in first cost.

In coupling lengths of shafting together, the plan of using a solid sleeve or box of metal keyed to the shaft is still generally adhered to in this country, we presume, as a rule, on account of its cheapness, as it is both clumsy and inconvenient. A light and convenient form of coupling much used in America, and known as the double cone vice coupling, consists of a cylindrical barrel, which couples the shafts. The inside of this barrel is turned to a double conical form; between the barrel and the shaft are fitted two sleeves, the outsides of which are conical and fit the box, and the insides are bored to fit the shaft. These sleeves are cut completely through on one side, and are made to close concentrically upon the shaft by means of three square bolts fitted in slots cut into the sleeves and barrel, and running parallel to the shaft; these couplings have the advantage of being easily uncoupled in the centre of a shaft for placing or removing pulleys, without the great trouble of drifting keys or the expense of using split pulleys, as is the case with the ordinary box coupling.

The most improved form of plummer-blocks are made on the principle of the universal or ball and socket joint. The advantage of this plan is that, in whatever direction the shaft may incline, there is an equal wear or strain upon the whole surface of the bearing, and should the

plummer-blocks be set somewhat out of truth, the ball and socket joint allows the bearings to adjust themselves in line. The base of plummer-blocks and the face of sole-plates and wall-boxes should in all cases be planed, as any little outlay in this way is amply repaid by the

shafting running truer, and being less likely to get out of line. All parts of a plummer-block should be turned and planed together.

Our illustration (Fig. 7) represents the section of a plummer-block such as we have described, and which will be found to answer well. A further improvement in its construction, over ordinary bearings, is the simple arrangement for lubrication. This consists of a dovetail slot running nearly the whole length of the top half of the bearing, which is packed in with cotton and saturated with oil, and being constantly in contact with the shaft, a film of oil is spread over the whole wearing surface of the bearing. Hanging brackets and bearings should in all cases be planed and turned together.

In fixing shafting, it is important that it is made to run at a dead level; this can be best done by means of a straight-edge and spirit-level. In the first place, take the straight-edge and rest it on the bottom bearing of two or more of the plummer-blocks, and pack them up till the spirit level stands exactly true, then try the shaft in several places. Care must be taken that the driving pulleys on the main shaft and the pulleys on the machines or countershafts are exactly linable with each other. This can be ascertained by means of a long straight-edge, by placing it to bear evenly on the edges of the driving pulley and setting the other pulley to it; if the driven pulley is some distance off, in the place of a straight-edge, a plumb-line or piece of string may be used in a similar way this gives you a line at right angles with the shaft. One shaft can be set at right angles with another by using a square on the main shaft and by stretching your plumb-line from it. The main shaft should, in the first instance, be set from the driving wheel on the engine, and not from the walls of the building, as is sometimes done, as these may run out of truth; the engine, however, should be set as nearly parallel with the walls as possible.

Cross shafts, vertical shafts, and toothed gearing should in saw-mills be avoided as much as possible, and one line of horizontal shafting should not be set above another in a perpendicular line, as the driving power of the belt under these circumstances is lessened. Lengths of shafting should be calculated so that as far as possible, when erected, the couplings should come close to a bearing.

When several lines of main shafting running parallel to each other are in use, the pulleys receiving and transmitting the motion are best placed close to each other on the same side of the mill, with bearings well up on either side of them; the strain on the shafts is thus more equalised, as the belts pull in both directions.