221 



BLOCK. 



BLOCK. 



222 



the frame which contains the block, and works in a concave screw, 

 which is cut in the transverse piece 1 1, the latter being fixed to the 

 table or stage. 



E F is an axle which terminates with a crank at E and carries at the 



moved along the arc. Thus, the tool acting against the block during 

 ,ho revolution of the latter with the wheel, and being itself in motion 

 lorizontally, the face of the block is brought to the form of a segment 

 of a sphere. Each block is then turned on its particular axis : first 

 one quarter round, then another quarter, and finally a third quarter 

 round : and in each of these positions an edge or side of the block is, 

 >y the tool, brought to a form similar to that which was given to the 

 irst face ; the last of the four sides being completed after each block 

 ias been turned three quarters round on its own axis. The ten blocks 

 ire then removed and ten others put in their places, to be shaped in 

 ike manner. 



The blocks are not turned on their several axes by hand, the machine 

 :ontainiug an ingenious contrivance by which such revolutions are 

 effected. In the following cut, A B is the axle of the double wheel, of 

 which A c, B D represent two of the radii, and E one of the blocks at 

 ;he circumference. A bevilled wheel F G is fitted on the axle of the 

 double wheel, and, in the teeth of this, work as many pinions, H, K, &c., 

 as there are blocks ; each pinion has an axle L M in the direction of a 

 radius of the great wheel, and extending as far as the circumference of 

 the latter ; near the extremity M is cut what is called a perpetual 

 screw, whose threads work in the grooves of a pulley-shaped wheel N, 

 on the axle of which is the block E. 



opposite extremity the fly-wheel G H, the revolving motion being com- 

 municated from the engine by a strap passing over the cylinder K. 

 The circular motion of the crank at E produces by means of the bent 

 rod L, which turns on a joint at d, a reciprocating motion vertically in the 

 rod e which passes through a collar at/: to the lower part of this rod 

 is made fast the steel chisel g by which the mortise is to be cut ; and 

 it may be easily understood that, if two or three mortises are to be cut 

 at the same tune, as many chisels may be fixed, in line, parallel to one 

 another, in a frame which is carried by the rod e. On the screw c D is 

 a toothed wheel h, and below it is a small wheel k which can be turned 

 round by means of the handle at m, and thus a small motion may be 

 given to the frame a a in order to bring the hole previously bored m 

 the block vertically under the chisel </. The axle E F carries an 

 eccentric wheel n (seen edgeways), on the circumference of which rides 

 one extremity p of a bent lever p q, the lower branch of which lies 

 tangentially on the top of a ratchet wheel r : the inferior surface of 

 ranch has a noteh, the sides of which, by the movement of the 

 eccentric wheel, are made to act on a tooth of the wheel r ; and thus, 

 the axle c D being turned, the frame a a is moved a little way towards 

 the cross-piece 1 1. This movement always follows immediately after 

 the chisel has made a descent, and thus there is presented a new part 

 to be cut out from the block. Since the chisel goes quite through the 

 block at each descent, and the movement is very rapid, the mortise is 

 quickly made. 



The extremity q of the bent lever pq rests upon a lever whose 

 fulcrum is at v, and this rests at w on the bent lever texy, whose ful- 

 cra m i at x, and when by the motion of the frame a a the notch at y 

 falls over the extremity z of a projection on the side of the frame, the 

 notch in the branch 7 is lifted above the top of the wheel r, and the 

 mortise being completed, the frame with the block moves no further. 

 The cylinder K is hollow, and within it, upon the axle E F, is a cone 

 which, while it turns with the axle, is capable of being moved back- 

 wards or forwards on the latter by means of a lever not shown in the 

 cut : when this cone is thrust as far as it can go into K, the friction is 

 great enough to allow the axle to be turned with the fly-wheel anc 

 cylinder ; but, un drawing the cone towards E, its surface is disengagec 

 from the interior surface of K, so that the axle E F no longer moves 

 with the fly-wheel. It is while the axle ceases to revolve that the 

 mortise block is removed, and one on which the operation is to bo 

 performed is put in it place. 



The block ia subsequently submitted to the action of a circular saw 

 by which the corners are cut off, and it is made to assume the form o 

 an octangular prism ; in this state it is removed to what is called thr 

 shaping machine, hi order to be reduced to the requisite figure. 



The shaping machine consists of two wheels connected together and 

 turning on the game horizontal axle ; they carry between the interior 

 surfaces of their rims ten blocks at equal distances from one another 

 on the circumference ; and at first the blocks are disposed so that the 

 mortises in each are perpendicular to a plane passing through the 

 common axis of the two wheels, the axes of the blocks remaining 

 always parallel to that axis. The wheels are made to revolve by a 

 strap passing over a cylinder on the axle; the cylinder being in con- 

 nection with the steam-engine : the cutting tool is applied, on a level 

 with the axis of the wheels, to a horizontal frame which has the form 

 of a circular arc, the centre being in the middle of that axle ; and 

 while the edge of the tool is pressed against the block it is slowly 



During the process of shaping the blocks, the wheel F G revolves 

 with the great wheel, carrying with it the pinions H K, &c., and their 

 axles L M, &c., the pinions not changing their places on the circum- 

 ference of F G, and consequently the blocks having no movements on 

 their particular axles. But when the first faces of the ten blocks have 

 been shaped, the whole machine is detached from the engine, and the 

 wheel F G, which is capable of turning freely on the axle of the great 

 wheel, being held fast, the latter is turned round by hand ; this causes 

 the pinions H K, &c. to move on the circumference of F G, and, at the 

 same time to revolve on their own axes ; thus the axles L M, &c. 

 revolve, and, on account of their connection at N, &c., with the axles of 

 the blocks, the latter revolve also on their axes. The numbers of the 

 teeth are so proportioned that four revolutions of the great wheel, 

 while F o is held fast, will cause each block to turn a quarter round ou 

 its own axle : this brings a new side of each block to the circumference 

 of the wheel, and the whole machine being then re-connected with the 

 steam-engine, the process with the tool is again carried on till the new 

 side of the block is shaped ; the machine is then released from the 

 engine, the blocks turned as before another quarter round, and so on. 



The part a b represents the shaping tool, which slides between the 

 two plates c and d of a frame which is made to slide upon the circular 

 arc p Q towards either of its extremities by moving the handle B ; and 

 while the tool is thus made to move slowly on the arc, it is kept close 

 to the block by pressing on the handle s, which turns on a pivot at e, 

 against a pin at 6. 



Lastly, the blocks are taken to what is called the scoring-machine, 

 by which there are cut on each of the faces the two grooves intended 

 to receive the rope by which the block is to be suspended when in use : 

 this operation is performed by means of two cutting tools, with curved 

 edges, fitted at the opposite extremities of a small brass wheel which 

 revolves on an axle by the connection of the latter with the steam- 

 engine : the block is fixed in a frame in an inclined position, so that 

 the cutting tools form a groove which commences near the pin-hole of 

 the block and deepens gradually towards either extremity. 



The sheaves are made of lignum vitfe, and plates of the required 

 thickness being cut from the tree, each of them has a circular form 

 given to it by means of a trepanning, or crown saw, a cylinder of steel 

 having teeth on one of its edges, and having on its axle a tool for 

 boring the centre hole through which the pin is to pass ; the plate of 

 wood being fixed in its place, the workman by a lever presses the saw 

 and centre-bit against it ; and these by revolving rapidly, both give a 

 circular form to the plate and bore the hole in its centre. 



The sheave is then to be prepared to receive in its centre the metal 

 cook or ring through which the pin is-to pass ; for this purpose it is 

 laid horizontally on a plate, which may be kept at rest, or turned round 

 on its axis, as may be required ; a drill, or cutting tool, in a vertical 

 position, is made to form in succession three semicircular excavations 

 of small depth at equal distances from one another about the centre 

 hole. During the cutting of each of these the plate carrying the 

 sheave is fixed, but in each interval it is turned one-third part round, 

 by which means the tool is enabled to enlarge the centre hole to a 

 small depth, quite round the latter ; thus the side of the sheave is 

 countersunk about its centre in the form of a circle having three 

 segments cut in its circumference : the like countersinking then takes 

 place on the other side of the sheave. The coak, which is made of 



