The Workshop.

Otago Witness, Issue 1297, 7 October 1876, Page 3

The Workshop.

FACTS AND SIMPLE FORMULA FOR MECHANICS, AND ENGINEERS.

Velocity of circular saws at periphery, 6,000 to 7,000 feet per minute. Rate of feed for circular saws, 15 to 60 feet per minute. Velocity of band saws, 3,600 feet per minute. Velocity of gang saws, 20 inch stroke, 120 strokes per minute. Velocity of scroll Baws, 600 to 800 strokes per minute. Velocity of planing machine cutters at periphery, 4,000 to 6,000 feet per minute. Travel of work under planing machine, one-twentieth of an inch for each cut. Travel of moulding machine cutters, 3,500 to 4000 feet per minute. Travel of squaring up machine cutters, 7000 to 8000 feet per minute. Speed of wood carving drills, 5,000 revolutions per minute. Speed of machine augers, l£ inches diameter, 900 revolutions per" minute. Speed of machine angers, f inch diameter, 1,200 revolutions per minute. Gang saws require, for 45 superficial feet of pine per hour, 1 horse power indicated. Circular saws, for 75 superficial feet of pine per hour, horse horse power indicated In oak or hard wood, f of the above quantities require 1 horse power Indicated. The area of a safety valve Bhould be •006 times the area of the fire grate.

On railway car axles, 20 pints of oil lubricate 8 journals of care for s,ooo miles, or 1 pint for 250 miles. The following is the effective horse power for different water motors, theoretical power being 1 : Undershot water wheels, 0*35 ; Poncelet's undershot water wheel, o'6o ; breast wheel, 0*55 ; highbreast, 0 60 ; overshot wheel, o'6B ; turbine, o'7o ; hydraulic ram raising water, 0-60 ; water pressure engine, 0 - 80. The following are tho ordinary dimensions of windmill sails : Length of whip, 30 feet ; breadth at base, 12 inches ; depth, at base, 9 inches ; breadth at tip, 6 inches ; depth at tip, 4£ inches. The effective horse power is found by dividing the product of the total area of sails in square feet and the cube of the velocity in feet per second of the wind by 1,080,000. Rule for speed of screws : Velocity in miles per hour = pitch of screw in feet multiplied by the number of revolutions par minute, and divided by 88. With hydrogen gas, having a buoyancy of about 13 3 feet to 1 lb., the diameter of balloons = the cube root of 25 5 times the weight to be raised, including that of the balloon itself, or the weight =o*o392 times the cube of the diameter.

The unit of heat is the quantity required to raise the temperature of 1 grain of water at its maximum density 1° Fah. The absolute mechanical equivalent thereof is £72 foot grains, and the thermal equivalent of the absolute unit of work -0-000040224.

The actual horse power of pumping engines = quantity of water raised per minute in cubic feet multiplied by height elevated in feet, multiplied by 0.0023. The indicated horse power of engines is found by dividing twice the product of the area of the piston in square inches X the average pressure of steam in lbs. per square inch in cylinder x the number of revolutions per second X the length of the stroke in feet by 550.

Useful numbers for pumps : The square of the diameter multiplied by the stroke, multiplied by 0"7854, gives capacity of the pump cylinder in cubic inche3 ; by 0-002833, in gallons; by 0*0004545 in cubic feet ; 0 "02833, in lbs. fresh water. Resistance in lbs. per tun on different roads, exclusive of gravity : Stone tramway, 20 ; paved roads, 33 ; macadamized roads, 44 to 67 ; gravel, 150 ; soft sandy and gravelly ground, 210. Laths are 1£ to 1£ inches by 4 feet in length, are usually set J of an inch apart, and a bundle contains 100.

A tarred rope is about one -fourth weaker than untarred white rope. Tarred hemp and manilla ropes are of about equal strength. Wire rope of the same strength as new hemp rope will run on the same sized sheaves ; but the greater the diameter of the latter, the longer it will wear. One wire rope will usually outlast three hemp ropes. Running wire rope needs no protection ; standing rigging should bo kept well painted or tarred. The coefficient of friction of leather belts over wooden drums is 047 of the pressure, and over turned cast-iron pulleys o'2B of the pressure. A mixture of 9 parts phosphate of soda, 6 parts nitrate of ammonia, and 4 parts diluto nitric acid is a freezing compound which will cause a fall in temperature of 71°Fah.

Three fourths of a cubic foot of water evaporated per hour will produce 1 horse power. Cold blast iron is stronger than hot blast. Annealing castiron diminishes its tensile strength.

The safe load in tuns which an iron chain will withstand equals the square of the diameter divided by 0,