MOUNT KE.MBLA COLLIERY. 



287 



thread of the bar. The thread and cutters may be arranged 

 with a left or right spiral, according to the direction it is 

 desired to work in ; but in either case the bar must be rotated 

 in the proper direction, or else the coal cuttings will not be 

 filled out. The bar has a rotary and reciprocating movement 

 which gives a chipping and shearing action, and prevents 

 the bar from clogging, and the cutter bar from working in a 

 groove. The spiral thread round the bar acts as ait 

 Archimedean screw and conveys the cuttings away in a con- 

 tinuous stream. If the coal was not got rid of, it would 

 pack into a hard mass, which would have to be loosened by 

 hand. A cleaner-bar is placed 4in. behind the cutter, 

 which scrapes the cuttings close to the cutter bar. This- 

 machine works well in coal, but the cost of repairs is consid- 

 erable when cutting into rock or pyrites. Two men are re- 



Fig. 151 Starting a cut with the Pick-quick. 



quired for each machine. The bar can move both vertically 

 through an angle of 2Udeg., and horizontally for ISOdeg. 

 For good floors, skids are better than wheels, for it saves 

 the cost of track-laying, which, when the machine works 

 fast, is difficult to do quickly enough. On skids the machine 

 runs smoother and with less vibration than on wheels; the 

 machine also cuts closer to the floor. The power required 

 to shift the machine on skids is not so very great, as it is 

 exerted relatively slowly. When starting a cut the bar lies 

 horizontally in line with the face of the coal ; the bar is then 

 revolved and carried to line on its horizontal axis, as it cuts 

 into the coal, until the bar is at right angles to the track ; it 

 then continues to cut the coal as the whole machine is pulled 

 forward (Fig. 151). The machine is self-propelling. A 

 long-wall machine may be worked so that it always cuts in the 

 same direction, and on reaching the end of the face it is 

 flitted back to its starting point along roadways ; or it may cut 

 to and fro across the face. The first method is generally em- 



