Model of boring plant (scale 1.10).

This model represents a complete apparatus for boring holes of from 4 to 6 in. diameter to a depth of from 60 to 80 ft.

It consists of a tripod with tubular legs, one of which is combined with a single-purchase hand-winch, which is provided with a strap brake. The legs are connected at the top by an iron ring, through which the boring rods pass when being uncoupled. The chain from the winch passes over a pulley at the top down to a block with a swivel hook. The holes are bored by rotating augers if the ground be soft, and by percussive chisels in hard ground or rock. For this latter process the top length of boring rod ends in an eye in which a combined hook and lever engages. This lever is attached to the hook of the lifting chain, and also catches the eye of the top boring rod, so that when the chain is wound in the rods are raised. The master-borer, who is holding the end of the lever with his right hand, and the top of the rod with his left, rotates the rods a certain amount, and then, by depressing the lever, releases them. The rod, in falling, chips the bottom of the hole. The rods are again lifted by the assistant at the winch and the operation repeated. After a time the accumulation of chips necessitates the hole being cleared, which is done by withdrawing the rods and introducing a sand pump or sludger. This consists of a tube provided with a ball valve below, so that the sludge will readily enter but cannot return, and can thus be brought to the surface. The pump is alternately lowered and withdrawn until the hole is sufficiently cleared to continue the boring. there are various forms of boring tools and earth augers, together with the wrenches employed for screwing up and unscrewing the boring rods and tools.