Page images

this product by the product of the two parts of the shaft when the load is carried at the center. The fourth root of this quotient will be the diameter required. The shaft in a line which carries the receiving pulley, or which carries a transmitting pulley to drive another line, should always be considered a "head shaft," and should be of the size given by the rules for shafts carrying main pulleys or gears.


(Jones Laughlin Steel Co., Pittsburgh, Pa.)

Don't overtax belts by overloading them or by running them tighter than necessary.

The whole arrangement of shafting and pulleys should be under the direction of a mechanical engineer or competent machinist. Destruction of machinery and belts, together with unsatisfactory results in the business, is a common experience which may, in most cases, be traced to want of knowledge and care in the arrangements of the machinery and in the width and style of the belts bought, and in the manner of their use, while the manufacturers of the "outfit" are often blamed for bad results which are caused by the faulty management of the mill owner himself.

Having properly arranged the machinery for the reception of the belts, the next thing to be determined is the length and width of the belts.

When it is not convenient to measure with the tape line the length required, the following rule will be found of service: Add the diameter of the two pulleys together, divide the result by 2 and multiply the quotient by 34, then add this product to twice the distance between the centers of the shafts and you have the length required.

The width of belt needed depands on three conditions: 1. The tension of the belt. 2. The size of the smaller pulley, and the proportion of the surface touched by the belt. 3. The speed of the belt.

The working adhesion of a belt to the pulley will be in proportion both to the number of square inches of belt contact with the surface of the pulley, and also to the arc of the circumference of the pulley touched by the belt. This adhesion forms the basis of all right calculation in ascertaining the width of belt necessary to transmit a given horsepower.

In the location of shafts that are to be connected with each other by belts, care should be taken to secure a proper distance one from the other. It is not easy to give a definite rule as to what this distance should be. Circumstances, generally, have much to do with the arrangement and the engineer or machinist must use his judgment, making all things conform, as far as may be, to general principles. This distance should be such as to allow of a gentle sag to the belt when in motion.

A general rule may be stated thus: When narrow belts are to be run over small pulleys, 15 feet is a good average, the belt having a sag of 11⁄2 to 2 inches.

For larger belts, working on larger pulleys a distance of 20 to 25 feet does well, with a sag of 21⁄2 to 4 inches.

For main belts working on very large pulleys, the distance should be 25 to 30 feet, the belts working well with a sag of 4 to 5 inches.

If too great a distance is attempted, the weight of the belt will produce a very heavy sag, drawing so hard on the shaft as to produce great friction in the bearings, while at the same time the belt will have an unsteady flapping motion, which will destroy both the belt and machinery.

If possible to avoid it, connected shafts should never be placed one directly over the other, as in such case the belt must be kept very tight to do the work. For this purpose, belts should be carefully selected of well stretched leather.

It is desirable that the angle of the belt with the floor should not exceed 45°. It is also desirable to locate the shafting and machinery, so that belts should run off from each shaft in opposite directions, as this arrangement will relieve the bearings from the friction that would result when the belts all pull one way on the shaft.

The diameters of the pulleys should be as large as can be admitted, provided they will not produce a speed of more than 3,750 feet of belt motion per minute. Some authorities limit this speed to 3,000 feet.

The pulleys should be a little wider than the belt required for the work.

The motion of driving should run with and not against the laps of the belt.

Tightening or guide pulleys should be applied to the slack side of belts and near the smaller pulley.

Quick motion belts should be made as straight and as uniform in section and density as possible, and endless if practicable, that is, with permanent joints.

Belts which run loose, will of course, last much longer than those which must be drawn tightly to drive-tightness being evidence of overwork and disproportion. Never add to the work of a belt so much as to overload it.

The transmitting power of a double belt is to that of a single belt as 10 is to 7. In ordering pulleys, the kind of belt to be used should always be specified.

The strongest part of belt leather is near the flesh side about the way through from that side. It is therefore desirable to run the grain (hair) side on the pulley, in order that the strongest part of the belt may be subject to the least wear.

The flesh side is not liable to crack, as the grain side will do when the belt is old, hence it is better to crimp the grain than to stretch it.

Leather belts run with grain side to the pulley will drive 30 per cent more than if run with flesh side. The belt, as well as the pulley, adheres best when smooth, and the grain side adheres best because it is smoothest.

A belt adheres much better and is less liable to slip when at a quick speed than at a slow speed. Therefore, it is better to gear a mill with small pulleys and run them at a high velocity than with large pulleys and to run them slower. A mill thus geared costs less and has a much neater appearance than with large heavy pulleys.

Belts should be kept clean and free from accumulations of dust and grease, and particularly from contact with lubricating oils, some of which permanently injure leather.

Leather belts must be well protected against water, and even moisture.

India rubber is the proper substance for belts exposed to the weather, as it does not absorb mositure and stretch and decay. Belts should be kept soft and pliable.

Tight Belts

Clamps with powerful screws are often used to put on belts with extreme tightness, and with most injurious strain upon leather. They should be very judiciously used for horizontal belts, which should be allowed sufficient slackness to move with a loose undulating vibration on the returning side, as a test that they have no more strain imposed than is necessary simply to transmit the power.

On this subject, the following from a New England cotton mill engineer of high reputation and large experience is entitled to careful consideration:

"I believe that three-quarters of the trouble experienced in broken pulleys, hot boxes, etc., can be traced to the fault of tight belts. The enormous and useless pressure thus put upon pulleys must in time break them, if they ate made in any reasonable proportions, besides wearing out the whole outfit and causing heating and consequent destruction of the bearings. If manufacturers realized how much this fault of tight belts cost them, in running their mills, probably they would wake up.



(Jones Laughlin Steel Co., Pittsburgh, Pa.)

In general the term "gearing" is applied to all the parts of machinery by which motion is transmitted, especially is it employed for wheels, whether friction or tooth. Tooth wheels are "in gear" when their teeth are engaged together; "out of gear" when separated.

Spur gears are wheels with the teeth or cogs ranged round the outer or inner surface of the rim, in the direction of radii from the center and their action may be regarded as that of two cylinders rolling upon one another.

Bevel gears are wheels the teeth of which are placed upon the outer periphery in a direction converging to the apex of a cone-and their action is similar to that of two cones rolling upon each other.

When two bevel wheels of same diameter work together at an angle of 45° they are called "mitre wheels."

The teeth are called "teeth" when they are of separate material. Wheels in whose rim "cogs" are inserted are called "mortise wheels."

The straight line drawn from center to center of a pair of wheels is called the "line of centers."

The pitch line by which the size of a wheel is always given, represents, as noted above, the touching of two cylinders rolling upon one another, and is the line or circle on which the pitch of the teeth is measured.

The pitch is the distance between the centers of two adjacent teeth measured at the pitch line.

Diametral pitch is the number of teeth to each inch of diameter of pitch line or circle.

Circular pitch is the distance from center to center of two adjacent teeth on the pitch line.

In calculating the speed of gears, multiply or divide, as the case may be, by the number of teeth (instead of diameter as for pulleys) and use the rules following:

Rules for Calculating Speed of Pulleys

1. The diameter of the driver and driven being given to find the number of revolutions of the driven.

RULE: Multiply the diameter of the driver, by its number of revolutions, and divide the product by the diameter of the driven; the quotient will be the number of revolutions.

2. The diameter and the revolutions of the driver being given to find the diameter of the driven that shall make any given number of revolutions in the same time.

RULE: Multiply the diameter of the driver by its number of revolutions and divide the product by the number of revolutions of the driven; the quotient will be its diameter.

3. To ascertain the size of the driver.

RULE: Multiply the diameter of the driven by the number of revolutions you wish to make and divide the product by the revolutions of the driver; the quotient will be the size of the driver.

The above rules are practically correct. Though owing to the slip, elasticity and thickness of the belt, the circumference of the driven seldom runs as fast as the driver.

Belts, like gears, have a pitch line, or a circumference of uniform motion. This circumference is within the thickness of the belt and must be considered if pulleys differ greatly in diameter, and a required speed is absolutely necessary.


(Jones Laughlin Steel Co., Pittsburgh, Pa.)

The best shingles are of white cedar. When of good quality they will last 40 to 50 years in the northern states. Cypress and white pine are much used for shingles but will not last half as long as white cedar.

Shingles are packed 250 to the bundle, or 4 bundles to 1,000. One bundle of 16-inch shingles will cover 30 square feet. One bundle of 18inch shingles will cover 33 square feet.

When laid 51⁄2 inches to the weather, 5 pounds 4d. or 334 of 3d. nails will lay 1,000 shingles.

Note: On the Pacific Coast redwood is, next to the cedar, the best and most economical shingle to use.


(Jones Laughlin Steel Co., Pittsburgh, Pa.)

Good paint properly applied is an investment rather than an expense, and the purer the material the better the investment.

Exterior surfaces not previously painted should be given three coats

and never be done at a temperature less than 50 degrees or in damp or frosty weather.

The surface should be perfectly dry and all knots and sap streaks in lumber should be covered with grain alcohol shellac before priming coat is applied. All nail holes should be filled with putty after priming.

PRIMING COAT: 10 pounds pure white lead, 5 pints pure raw linseed oil, 4/5 pints pune turpentine, 1/6 pint pure turpentine drier.

SECOND COAT: 15 pounds pure white lead, 4 pints pure raw linseed oil, 3/10 pint pure turpentine, 3/20 pint pure turpentine drier.

THIRD COAT: 144 pounds pure white lead, 41⁄2 pints pure raw linseed oil-pint pure turpentine and 18-pint pure turpentine drier.

First coat will cover 500 square feet and the second and third 600 square feet.

Surfaces which have previously been painted will only require two coats. Remove all grease and dirt.

Where paint is blistered or peeled it should be burned or scraped and the bare spots treated and primed like new work.

To make one gallon of paint:

FIRST COAT: 121⁄2 pounds pure white lead, 4 pints pure raw linseed oil, 1 pint pure turpentine, % pint pure turpentine drier. For the second coat use formula for third coat for new work.

Allow paint to dry thoroughly before applying additional coats.


For interior woodwork, increase the oil from 15% to 20% and the turpentine from 50% to 75% in the priming coat. In second and third coats increase raw linseed oil 12% and 25% respectively.

The same general conditions apply to the use of ready mixed paints. For ordinary work these paints should be thinned as follows:

In priming new work add about 1⁄2 gallon of raw linseed oil to 1 gallon of paint.

For second coat add 1⁄2 to 1 pint of turpentine to the gallon. For third coat use the paint as it comes from the can.

For old work add to each gallon 1⁄2 pint of turpentine and 3 pints of raw linseed oil.

To Soften Old Putty

To remove old putty from broken windows, dip a small brush in nitro-muriatic acid or caustic soda and with it paint over the putty that adheres to the broken glass and frames. After one hour the putty will be so soft as to be easily removed.


(Jones Laughlin Steel Co., Pittsburgh, Pa.)

Cement may be divided into four general classes: Portland, Natural, Pozzuolana and Mixed. Their relative values are about in the order named.

PORTLAND CEMENT is a product obtained by crushing and grinding, after heating to the sintering point, a mixture of limestone, marl, chalk, or hydraulic limestone with clay, and is quite distinct from the other kinds of cement.

« PreviousContinue »