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MODERN STEAM PRACTICE.

Strength of round shafting to resist lateral stress .-—Multiply thelength of shaft supported at both ends in feet by the weight or stressapplied at centre, divide by the constant 700 for wrought iron, andthe cube root of the quotient is the diameter in inches; when theweight is equally distributed the constant is 1400.

Shaft bearings. —The bearings for the shafting are hung from therafters, girders, or placed on brackets bolted to the walls of the shopor factory; the strength of the brackets depends on the amount ofoverhang. The proportions of the pillow blocks may be taken fromthe diameter of the shaft; ordinary pillow blocks have a proportionas follows, when the diameter is given:—

Diameter multiplied by ‘4 equals the thickness of cover.

Do. ‘3 ,, thickness of sole.

Do. '25 ,, diameter of bolts when two are used.

The thickness of the bottom and top brasses equals one-seventh ofthe diameter of the shaft, and at the sides three-fourths of the bottomthickness will suffice.

Couplings and distance between pillow-block Supports. —The coup-lings for general shafting are of cast iron. When D equals thediameter of shaft, B the diameter of the coupling, and A the lengthof the coupling box or short cylinder embracing the ends ofshafting—

A = the diameter multiplied by 3*6,ß = the diameter multiplied by 2*4,

that is for medium sizes; but when the shaft is of extra diameterthis proportion can be reduced, and wrought-iron rings shrunk onthe ends; the coupling is secured with ordinary keys, one beingquite sufficient for the usual run of shop and factory shafting.For ordinary shop shafting, 3 inches diameter, the distance betweenthe centres of the bearing is from 9 to 10 feet. To find thedistance for other sizes, square the diameter of the shaft; extractthe cube root, and multiply by 4’5, or 5 where there is no powertaken off between, and the product is the distance between centresin feet.

Pulleys. —The curve or convexity of pulleys driven by means ofbelting is about y 2 inch per foot in width. The final speed of aseries of pulleys is found in the same way as a series of toothedwheels, provided there be no slip. The velocity of the drivingpulley is multiplied by the drivers and divided by the driven, whichgives the final velocity. It is usual to split pulleys and bolt them