REVOLVING ROPES.

The above mentioned convolutions do not as a rule take the circuit of the pulleys but are usually conducted along the trailing span to the point of seizure where the periphery in actual contact

at the moment is held and carried forward. Nor are they always constant; but are sometimes so erratic that ropes will fix themselves for a period and then roll over to be compressed at another point, until their sections assume irregular polygons.

When the rolling action is continuous the whole surface of the ropes so acted upon becomes perfectly round and bright like the two middle ones in the drive of four reproduced by Figure 39 as distinguished from the rougher appearance of their fellows.

This deleterious action is not always avoidable even in angular grooves unless they are moderately acute. Whatever the cause, it is computed that the life of a rope is reduced by at least onethird when it revolves.

ANGULAR GROOVES.

Curves disallowed permit only the angular groove. Undoubt

ably every rope has its most suitable groove angle, but as the providing of a whole range of templates to agree with every advance in size would perhaps prove more inconvenient than advantageous. We have fixed upon two leading angles for all driving ropes viz;- 40 degrees for those above 1 inch diameter and 30 degrees below that size; excepting however the small bands used for driving cotton machinery, say 11⁄2 inch diameter and even less, when angles so sharp as 15 degrees are brought into requisition.

In setting out a groove it should always be borne in mind that a rope is to all intents and purposes an elastic wedge and reaches. its highest driving capability when it is pressed to the shape of the groove itself. This cuneiform ought therefore always to be anticipated for if the sides of the groove are merely shown as tangents to the circle representing a given diameter of rope, there is always the danger of making the groove too shallow so that when the compression takes place the rope is liable to find its way to the bottom or what is almost as detrimental, work upon the semi-circle with which grooves usually terminate, when grip is considerably weakened and slipping supervenes, the true indication of which is heated pulley rims.

Without appealing to the protractor a 40 degree groove may be set out as shown in Figure 40.

First set a circle of equal diameter to represent the rope, draw the vertical and horizontal centre lines. The chord of the arc A, B, then decides the position of the centre for rounding the bottom of the groove and when doubled along the horizontal line, points the apex of the inverted angle, the arms of which cut the circle at B, B and also through the upper horizontal line at C, C.

The length of the midfeathers is decided by a horizontal line passed midway through the arc A, B, or its counter part.

SETTING OUT A 30 DEGREE GROOVE.

The only alteration in the above method when drawing a 30 degree groove is the length of the measuring staff, which, instead

HOW TO SET OUT A GROOVE OF 40 DEGREES.

of being represented by the chord A, B is extended to a point where a line resting at 45 degrees from the centre of the rope intersects the circle at C. This line (B, C) measures the depth of the groove and repeated, points to the apex of the angle.

Grooves having no power to transmit but which are merely used to bear up or conduct ropes out of the straight driving path, should be so constructed that they (the ropes) may rest easily at the bottom while the midfeathers open outwards. The pitch of these grooves should, of course, correspond with the transmitters to which they are tributary.

FIGURE 42.-GROOVES
FOR CARRIER

PULLEYS.

When templates of existing groves are required, the quickest and surest way is to take plaster casts (the grooves being previously well greased). These give more readily measured definitions than may be secured by attempting to cut pieces of wood, tin or other available material to the desired shape.

Beyond incidental acknowledgements of its existence the medium of transmission has hitherto been scarcely mention

not because its importance is inferior to any other factor which plays a part in the general economy of the system, but from a desire to emphasize at this junction that much neglected phase of the question which deals with the composition and construction of driving ropes.

Many and various are the materials which have been pressed into the services of the rope maker; an almost infinite variety of fibres, through the whole ranger of hemps and flaxes from the coarse grained Manilla to the silk like Ramie, and finally cotton. Ropes have also been made from paper strips, but one experiment was more than enough to prove their inaptitude for the purpose, as the rope under trial collapsed after less than an hour's running.

MANILLA.

Owing it may be conjectured to the fact that rope driving was cradled in what may be styled the home of the Manilla trade, that material gained for a time precedence above all others, and if merely judged on the lines of resistance to tensile strains, would still hold the field.

The fibres are, however, of so harsh and wiry a nature that they cannot be compressed into a solid mass by the successive twisting operations to which they are subjected, but instead of forming a perfect impact, the strands merely rest upon each other, thus constructing what may be termed a spiral tube. The strands, therefore, scrub one upon another with every bend of the rope until the centre is reduced to a fine powder.

The permanent set is quickly reached while gripping power is so limited that any reduction in the pulleys from 45 diameters must be reciprocated with a corresponding increase in the amount of rope. An advocate of continuous driving recommends 60-rope diameters for manilla.

When the system was first introduced into the Lancashire district experiments were soon tried in the direction of applying cotton to the manufacture of driving ropes, seeing that no other material was found capable of transmitting power to the various motions of a cotton spinning mule, the particular ramifications