96 TRANSMISSION OF POWER 



Split wood pulleys are preferable in many cases, but shortlived. The best make is the Dodge split 

 wood pulley, costing for 24-inch diameter and 10-inch face .''ir20. Steel split pulleys are made by the 

 American Pulley Co., Philadelphia, Pa. 



So-called "clutch pulleys" consist of two wheels wedged one into the other, the inner one loose, 

 the outer one fastened onto the shaft. 



Iron pulleys must be absolutely symmetrical. 



Pulleys for stationary belts are slightly crowning, while those for shifting belts are straight faced. 



Pulleys for heavy work should be placed close to bearings of shaft. The main driving pulley must 

 stand between bearings not over four or five feet apart. 



The ratio between the speed of driving and driven pulley is inverse to the ratio of the diameters. 



(C) SHAFTING. Cold rolled shafting is said to have a torsional strength 30 per cent greater than 

 that of hot rolled shafting. 



The usual diameters of shafting in sawmills are from 1 '/j inches to 3V2 inches. The proper speed for 



D ' X R 



shafting is 300 to 400 revolutions and its transmitting power is given as — „^ horse-power. 



Herein stands: -D for diameter of shafting. 



R for revolutions of shafting per minute. 

 80 for a constant factor. 



Couplings by which the sections of shafting are joined should be close to a hanger or a support. 

 They should be easily detachable without driving keys. 



Shafting comes in sections usually 12, 14, 16, or 18 feet long. 



The section closest to the main driven pulley is often stronger than the other sections. 



The bearings should be long, say four times as long as the shafting is thick, and should have 

 self-lubricating devices. 



Hangers for 3-inch shafting and of 3-foot drop cost about #20 each. 



Bearing-boxes are lined with an anti-friction alloy melting easily and offering little friction even under 

 severe pressure. A space of '/s inch to Vl- inch is left between the cast-iron box and the shafting (journal) 

 to be supported. The box is held in a "babbitting jig" while the melted alloy is poured from a ladle. 

 Babbitt metal (invented by Isaac Babbitt) consists of about 96 parts tin, 4 parts copper and 8 parts antimony. 



Rules for shafting are: — 



1. Be sure that line of shafting is parallel to axis of driver. 



2. Place all heavy work on the main shaft and close to the main driver. 



3. Oil freely and watch bearings constantly. Oil after stopping work, while bearings are still warm. 



4. Drive only minor machinery from gear wheels. 

 Price of shafting is about 5c or 6c per lb. 



REMARKS: — Machinery is started by belt tighteners, the belt running over flanged pulleys, by 

 clutch pulley, by tight and loose pulley with shifting belt, by eccentric boxes, and by friction pulleys. 



A rotation is reversed by crossed belts (belt turning 180 degrees), or by paper friction pulleys, or by 

 forcing the belt against a driven pulley remaining outside the belt circuit (e. g., in double band mills). 



A rotation is turned at right angles by giving the belt a quarter-twist (90 degrees), or by gear and 

 pinion, or by beveled friction or by running the belt over an intermediate pulley, placed between driver 

 and driven at an angle of 45 degrees against each of them. 



Before building or before remodelling a mill, be sure to consult the insurance companies, submitting 

 mill plans. 



The insurance rates depend on the distance between the yard, boiler house, engine house, mill and 

 dry kiln; on building and roofing material ; height of buildings, smoke-stacks, parapets; system of dry kilns, 

 blowers, shaving vaults, &c. 



