THE FARMER'S MAGAZINE. 



535 



two large sheaves, so as to make only two three quarter 

 turns holding sufficiently tight in two V-shaped grooves. 

 To draw off the slack rope paid out from the drum, 

 and prevent any " kinking" between the drum and 

 the small moveable guide-sheaves, it was necessary to 

 hold up the rope some height above the ground by 

 means of suspension-pulleys supported by elastic india- 

 rubber springs. And this form of apparatus, attached 

 to an engine made locomotive by toothed gearing 

 connecting or disconnecting the crank-shaft and the 

 travelling- wheels, is that hitherto supplied by Mr. 

 Fowler to his customers. The results of their perform- 

 ance have been, as we said, very satisfactory ; but an 

 improvement has now been applied, which lessens the 

 number of bends in the rope to the lowest possible 

 number, and reduces the hauling mechanism to the unit 

 of simplicity. A drum has been invented, applied, and 

 proved by field-work of some extent, which holds the 

 rope by only a single half-turn in its groove ; so that 

 now the endless rope passes directly on and off the 

 drum, as it goes round the anchor-sheave, without the 

 intervention of sheaves at both ends of the boiler, while 

 the "jibs" or suspension-pulleys with their elastic 

 springs are taken away. In passing on to the drum 

 the rope of course bends, and also bends from its curved 

 form in the act of straightening again as it leaves the 

 drum, so that it is bent twice ; besides which will occur 

 two slight bends in passing the moveable guide-sheaves 

 when the engine does not stand quite upright, or per- 

 pendicularly to the plane in which the ropes lead up to 

 and away from it. In the previous arrangement the 

 rope passing twice on and twice off the drum, and once 

 on and off of two sheaves or riggers, is bent eight times, 

 beside the bending which occurs in the guide-gheaves 

 and pulleys of the "jibs," amounting to four bends more. 

 Hence in the new machine there are only four bends of 

 rope instead of twelve. The consequent saviig of the 

 wear of rope can be appreciated only by persons who 

 are familiar from experience with the damage caused by 

 the frequent bending of wire-rope, especially round 

 small pulleys, and by the grinding of the rope against 

 the flanges of the sheaves. In the previous machine, 

 the rope, after passing one three-quarter turn round the 

 drum, is led round two large sheaves (at each end of the 

 boiler), before again passing round the drum. This is 

 found a much better arrangement than the wrapping of 

 the rope several times round two drums ; but sWU an 

 undue tension is occasioned by the unavoidably unequal 

 though slight wearing away of the grooves and running 

 bearings. All this is impossible with the new drum, 

 less friction and greater effective draught power being 

 gained, as well as wear saved. 



Let us now try to explain the action of the new drum. 

 It will be remembered that in the earliest arrangement 

 of grooved drums (shown at Chester in 1858) the rope 

 passed a number of half turns in round-bottomed 

 grooves conformed to the shape of the rope. This was 

 held from slipping solely by means of the bite or fric- 

 tional contact of the rope with the surface of the 

 grooves, arising from the pressure of the tight rope upon 

 the drum. It is a law in mechanics that friction in- 



creases in direct proportion to the jiressure applied for 

 forcing the surface together ; so that with double the 

 number of pounds pressure per lineal foot of rope, half 

 the length of rope in contact with a groove (or, in other 

 words, half the number of turns round the drums) 

 would give an equal amount of hold against slipping. 

 Now the weight or strain upon the rope, which causes 

 the pressure, could not be increased without a compli- 

 cated arrangement of pressing-wheels to squeeze the 

 rope at many points down into the grooves ; but the 

 groove itself might be so formed as to nip the rope, in- 

 stead of simply receiving it into a freely fitting space. 

 Accordingly the grooves were made of a V form ; the 

 rope, too thick to reach the bottom, became supported 

 by and jammed between the inclined sides : and, in 

 fact, the groove was (mechanically speaking) a female 

 wedge, just as a nut is said to be a female screw. Every- 

 body is familiar with the great multiplication of pres- 

 sure obtainable by the agency of the wedge ; and accord- 

 ing to the acuteness of the angle made by the sides of 

 the groove, a natural downward or inward pressure of 

 the rope, say of ten pound per lineal foot, will give in 

 the V groove a pinch or grip equivalent to the hold ob- 

 tained in a round groove by a pressure of twenty, fifty, 

 or more pounds per foot, Mr. Fowler adopted this 

 form of groove, as enabling him to save several turns 

 of rope; for with the V-grooved drums hitherto manu- 

 factured two three-quarter turns (equal to one and 

 a-half whole turns) give as much hold as the four half 

 turns and two quarter turns (equal to two and a-half 

 whole turns) of the former round-grooved drums. The 

 drum being fourteen feet in circumference, the length 

 of rope lying nipped in the V grooves (being two 

 three-quarter turns) was twenty-one feet ; and this was 

 the limit to which it could be reduced. For though the 

 sides of the groove may be made to hold against any 

 amount of slip by lessening their inclination to each 

 other until they are almost parallel, an acute angle is 

 found to incur excessive friction and cutting of the 

 rope against the sides of the groove in the act of enter- 

 ing and leaving ; and, indeed, the rope may be so firmly 

 jammed in the groove as to require considerable power 

 to release it where it ought to be paid out freely. There- 

 fore, to secure the many advantages of working with 

 only one half turn round the drum, it was necessary to 

 add to the nipping power of the groove without any 

 wedge-like action ; and the present improvement, long 

 in contemplation, has been tried, and proved perfectly 

 successful. All suggested complications of pressing- 

 wheels, weighted or spring levers, &c., being cast aside, 

 the working strain of the rope itself is still retained as 

 the sole originator of the pressure in the groove ; but it 

 is magnified upon the principle of the compound or bent 

 lever, instead of that of the friction-causing wedge. 

 For this purpose the sides of the groove are made move- 

 able in short segments ; the pieces of the upper and lower 

 side being opposite, and acting in pairs, and so hinged 

 respectively above and below the groove that when the 

 nipping faces are moved inwards towards the centre of 

 the drum, they approach more closely to each other ; 

 and, on the contrary, when moyed outwards they open 



M M 



