42 THOMAS COMMERFORD MARTIN 



weight of only about 2,500 pounds. As this machine rests 

 upon a wide flat shoe board it can easily be moved along the 

 face of the coal by ihe operator and his helper. A brief 

 description of the apparatus will be of interest. On an out- 

 side frame, consisting of two steel channel bars and two angle 

 irons riveted to steel cross ties, rests a sliding frame consisting 

 of a heavy channel or center rail, to which is bolted the cutter 

 head. The cutter head is made entirely of two milled steel 

 plates, which bolt together, forming the front guide for the 

 cutter chain. This chain, which is made of solid cast steel 

 links connected by drop forge straps, is carried around idlers 

 or sprockets placed at each end of the cutter head and along 

 the chain guides at the side to the rear of the machine, where 

 it engages with and receives its power from a third sprocket, 

 under the motor. The electric motor, which is of ironclad 

 multipolar type, rests upon a steel carriage, which forms the 

 bearing for the main shaft. The thin vein machine is equipped 

 with a self propelling truck, the motor which operates the ma- 

 chine being also geared to the truck axles. A reversing 

 switch is provided, so that the truck can travel in either direc- 

 tion, and when the machine has reached its stopping point, 

 either forward or backward, it is checked by an automatic 

 cut off. The return travel is made in about one fourth of the 

 time required to make the cut. Where the grades are heavy 

 the truck is of advantage, and where the room lies to the dip 

 it obviates the necessity of brushing down the roof for the 

 entry of mules. 



It is stated by Mr. Belden that many mines having only 

 28 to 30 inches of coal are being operated entirely with thin 

 vein machines, and that a fair average for such machines is 

 the cutting of at least 50 tons of coal per eight hour shift. 



According to the schedule adopted in No. 8 vein of Ohio 

 coal, the cost of pick mining in rooms is 90 cents per ton, 

 while the cost of machine mining in rooms is 11 cents, with 

 52^ cents for loading after machines in rooms. This shows a 

 saving through the substitution of machine mining for pick 

 mining of 26^ cents per ton. A liberal allowance for operation 

 and depreciation would leave a net saving of over 13 cents per 

 ton, and the four machines should produce at least 75,000 



