BORING 



453 



196 



is self-advancing, and self-adjustable, effected by the working cylinder being provided 

 with an exterior cylinder, in which it can slide. The motive pressure is constantly 

 tending to propel the working cylinder forward, but is retained by a screw, which is 

 prevented from turning by a paul, which the piston strikes when it makes a full 

 stroke, thus releasing the screw, and permitting the working cylinder to advance for- 

 ward as the hole increases in depth. The weight of blow which can be struck by this 

 machine is 500 Ibs. ; number of blows per minute 20 to 600. 



The inventor claimed the construction of rock boring machines, in which the piston 

 of the main cylinder distributes and exhausts the motive fluid to and from other cylin- 

 ders at distinct portions of the stroke. For further particulars and illustration, see 

 Specification No. 2,387, A.D. 1869. 



Scrgstrom's Sorer. This machine, used at the Perscberg Mines, near Philipstad, 

 in Sweden, is a modification of that constructed by Schumann, of Freiberg. The 

 machine consists of a cylinder 4 inches diameter, and a balanced slide valve. The 

 movement of the piston and valve is automatic, the advance of the apparatus is 

 effected by the hand. The length of stroke is 7 inches, cubic inches of air or steam 

 required per stroke 200, or 8 strokes per cubic foot. Speed from 200 to 350 blows 

 per minute. Pressure required to drive borer, 15 to 20 Ibs. per square inch. 



"Weight of machine, 122 Ibs. For additional particulars and illustrations, see 

 paper by C. Le Neve Foster, Miners' Association of Cornwall and Devonshire, 1867. 



Sack's Sorer. The lightness, suitability, and economical working of this drill, have 

 induced Prussian engineers to use it somewhat extensively, both in metalliferous 

 mines and collieries. Fig. 196 illustrates an arrangement of the drill and stand, 

 employed both in shaft and winze 

 sinking. The cylinder is 2i inches 

 diameter, borer rod l|ths inch di- 

 ameter, back rod 1 inch diameter, 

 valve rod -|ths inch diameter. The 

 valve is a simple plate ; one face 

 being on the port-ways leading to 

 and from the cylinder, the other 

 retained by a plate carrying the 

 valve arbor. The top of the back 

 rod carries a ring, to which is 

 attached a small rod for rocking 

 the valve-shaft. To this valve- 

 shaft is also attached a horizontal 

 rod, which carries two pauls, one 

 for turning the borer, the other for 

 advancing the cylinder through 

 the medium of a nut travelling on 

 the screw side bar. At a pressure 

 of 25 Ibs. per square inch, the borer 

 makes 400 strokes per minute, the 

 length of stroke being 5 inches. 

 The blow pressure is 116 Ibs., 

 return pressure 72 Ibs. About 45 

 cubic inches of air or steam are 

 required per stroke, or 38 strokes 

 per cubic foot. The area of steam 

 portway is ^ths of a square inch. 

 The rate of boring per minute in 

 basalt is 3 inches, coal sandstone 

 3 inches, quartz grauwacke 2 inches, 

 carbonate of iron 1 inch. One 

 borer requires about one horse- 

 power to drive it. 



Doering's Borer. This machine is worked by compressed air or steam, at a proa- 

 sure of about 35 Ibs. per square inch. The pressure fluid acts alternately on the front 

 and back of the main piston. The valve for the admission of compressed air, and for 

 the exhaust, is worked by two chambers in the main piston, one of these chambers 

 being always in communication with the main inlet of compressed air, the other 

 chamber in communication with the outer atmosphere. The valve has a separata 

 piston to work it; on the smaller side of the piston a constant pressure of air is main- 

 tained, a passage connects the other end of the cylinder, in which the valve-piston 

 Works, with a certain point of the main cylinder. The chamber with compressed air 



