Fig. 83.
The sheer-legs, made of sound Norway spars not less than 8 inches diameter at the bottom, are placed over the bore-hole for the purpose of supporting the tackle K K for drawing the rods out of or lowering them into the hole, when it is advisable to clean out the hole or renew the chisel. It is obvious that the more frequently it is necessary to break the joints in drawing and lowering the rods, the more time will be occupied in changing the chisels, or in each cleaning of the hole, and as the depth of the hole increases the more tedious will the operation be. It therefore becomes of much importance that the rods should be drawn and lowered as quickly as possible, and to attain this end as long lengths as practicable should be drawn at each lift. The length of the lift or off-take, as it is termed, depending altogether upon the height of the lifting tackle above the top of the bore-hole, the length of the sheer-legs for a hole of any considerable depth should not be less than 30 to 40 feet; and they usually stand over a small pit or surface-well, which may be sunk, where the clay or gravel is dry, to a depth of 20 or 30 feet. From the bottom of this pit the bore-hole may be commenced, and here will be stationed the man who has charge of the bore-hole while working the rods.
Fig. 84.
The arrangement, [Fig. 84], is intended for either deep or difficult boring. A regular scaffolding is erected upon which a platform is built. The boring chisel A is, as in the last instance, coupled by means of screw-couplings to the boring rods B. At each stroke two men stationed at E E turn the rod slightly by means of the tiller D D. A rope F, which is attached to the boring tool, is passed a few times round the drum of a windlass G, the end of the rope being held by a man at I. When the handles are turned by the men at L L the man at I pulls at the rope end, the friction between the rope and the drum of the windlass is then sufficient to raise the rods and boring tool, but as soon as the tool has been raised to its intended height the man at I slackens his hold upon the rope, and as there is insufficient friction on the drum to sustain the weight of the boring tools, they fall. By a repetition of this operation the well is bored, and after it has been continued a sufficient length of time the tiller is unscrewed, and a lifting dog, attached to the rope from the windlass, is passed over the top of the rods, and then a short top rod with a shackle is screwed on. The two men at the windlass draw up the rods as far as the height of the scaffolding or sheer-legs will allow, when a man at E, [Fig. 84], by passing a hand-dog or a key upon the top of the rod under the lowest joint drawn above the top of the hole, takes the weight of the rods at this joint, the men at L having lowered the rods for this purpose; with another key the rods are unscrewed at this joint, the rope is lowered again, the lifting dog put over the rod, another top rod screwed on, the rods lifted, and the process continued until the chisel is drawn from the hole and replaced by another, or, if necessary, replaced by some other tool.
When a deep boring is undertaken, direct from the surface, the operation had best be conducted with the aid of a boring sheer-frame such as is shown in the [frontispiece]. This consists of a framework of timber balks, upon which are erected four standards, 27 feet in height, and 9 inches × 1 foot thick, 3 feet 8 inches apart at bottom, and 1 foot 2 inches at top, as seen in the front and rear elevations. The standards are tied by means of cross pieces, upon which shoulders are cut which fit into mortise holes, and are fastened by means of wooden keys, the standards being surmounted by two head pieces 5 feet long, mortised and fitted. Upon the head pieces two independent cast-iron guide pulleys are arranged in bearings; over these pulleys are led the ends of two ropes coiling in opposite directions upon the barrel of a windlass moved by spur gearing, and having a ratchet stop attached to a pair of diagonal timbers, connected with the left-hand legs or standards of the sheers, near the ground. These ropes are used for raising or lowering the lengths of the boring rod.
Eight feet below the bearings of the top pulleys, a pair of horizontal traverses is fixed across the frame, supporting smaller pulleys mounted on a cast-iron frame, which is capable of motion between horizontal wooden slides. Over these pulleys is led a rope from a plain windlass fixed to the right-hand legs of the frame, to be used for raising or lowering the shell to extract the débris or rubbish from the hole.
The lever, 15 feet long, and 9 inches × 6 inches in section, is supported by an independent timber frame. It has a cast-iron cap, fastened by means of two iron straps, cast with lugs through which bolts are passed, these being tightened with nuts in the ordinary manner. The bearing-pins at a are 11⁄2 inch in diameter, and also form part of the lower strap. Upon the cap is an iron hook, to this a chain is attached carrying the spring-hook which bears the top shackle of the rods. The top of the bore-hole is surrounded by a wooden tube 1 foot in diameter, and surrounded by a hinged valve, whose action is similar to that of a clack-valve; this has a hole in the centre for the rods to pass up and down freely. The valve permits of the introduction and withdrawal of the tools, and at the same time prevents anything from above falling into the bore-hole.