50 



HARDWOOD RECORD 



April 10, 1921 



Electrically Driven Sawmills 



^By Allan E. Hall, Milwaukee, Wis. 



(Contiiinrd fnjin Mttich 2't Ikkuc) 



31 The average life of belts in a sawmill is not more than four 

 years, which means a running expense of 25 per cent of the total 

 belting cost yearly. The saving in oil, waste, etc., by changiug 

 over from shaft drive to motor drive has been estimated at 40 cents 

 per 1,000 feet of lumber per day. 



32 No attempt is made to give comparative figures for depre- 

 ciation, but the lumber manufacturer's accountant should consider 

 the low second-hand value of shafting equipment if it must be 

 moved and refitted for new conditions, as contrasted with the 

 easy interchangeability of motors. 



33 One of the lumbermen's mutual insurance associations recog- 

 nizes motor driving by a reduction of 25 cents in premium. 

 Another association, while not specifically recognizing electric 

 driving, usually makes a 5 per cent deduction from total premium 

 on account of the clear and open condition of the lower floor thus 

 produced. 



34 A gain in production of lumber is d"ue to the employment 

 of the constant-speed induction motor. The reduction of speed is 

 sometimes considerable in a sawing machine which is driven 

 through a long lineshaft, a countershaft and three belts — a com- 

 mon condition. 



35 Separate steam engines are also sometimes used in a belt- 

 driven plant to drive certain large machines (e. g., a gang mill) or 

 groups of machines. These engines proportioned for their average 

 load do not have the peak-carrying capacity of equivalent motors 

 with a large generator behind them. When tlic mil) is driven bv 



several steam engines of small size a reduction of shafting equip- 

 ment may be made, but each engine must carry its peak load with- 

 out help. Motors of corresponding horsepower rating connected 

 to one large generator will draw on an ample power reserve during 

 peak loads. Two gang mills have come under the writer's observa- 

 tion, of the same size and make, one driven by a steam engine 

 belted to it individually, the other motor-driven, both machines 

 nominally running at 225 r.p.m. The engine-driven gang ran at 

 225 r.p.m. light and 200 r.p.m. fully loaded. The motor-driven 

 gang ran at 225 r.p.m. light and about 223 r.p.m. loaded. As the 

 rate of lumber feed to the gang is governed by the speed, the 

 steam-driven gang was cutting about 10 per cent less than the 

 other. Cases are on record where mills by simply changing from 

 shaft drive to electric drive have increased their production 15 

 per cent. This problem of speed maintenance has not been suffi- 

 ciently studied b}' sawmill operators. 



Details of Motor Application 



36 The equipment for hauling logs into the sawmill and cross- 

 cutting them may be motor-driven. The remaining log-handling 

 equipment is actuated by direct-connected steam cylinders. These 

 steam-actuated machines are (1) the log kicker, which throws the 

 log sidewise out of the trough in which it has been hauled, into 

 the mill; (2) the log deck stop and loader, which holds the log in 

 position for loading and throws it on the carriage at the proper 

 time; (3) the "nigger," a machine which turns the log between 

 cuts so as to present different sides to the saw; and (4) the Pacific 



