Belt (mechanics)

“ The question of the minimum amount of slip of a belt in transmitting power from one pulley to another reduces itself to a question of creep, for it is possible to have belts large enough so that with proper tensions there will be no regular slip. With a difference in tension on the two sides and of elasticity in the belt, creep, however, is bound to take place. ”

“ The ordinary method of lacing a leather belt is to make the laces straight on the pulley side, all running in the same direction as the movement of the belt, and crossing them on the outside diagonally in both directions. ”

“ Joint A B is now only 10 inches, and we have 10 inches plus 4 inches plus 4 inches times 36 inches which equals 648 square inches, and the lead on the joint is now 14.44 pounds. You will readily perceive what an important part in the life of the belt, and the life of everything around the belt as far as that goes, the proper breaking of the upper and lower joints is. Of course the belt maker will tell you that his glue is just as strong as the leather itself, and he is about right as long as you keep the belt free from oil and water ”

“ But a crossed belt is open to the objection that the surfaces of the belt rub against each other at the point of crossing, which tends to rapidly wear out the laced joint of the belt. By crossing a vertical belt the lower pulley receives part of the weight of the belt. ”

“ Furthermore, belt connections are lighter and cheaper than gear-wheel or other rigid and positive connections, and hence the wide application of leather belts for the transmission of power, notwithstanding the slight variations of pulley velocity ratio due to the unequal elasticity of the various parts of the leather composing the belt. ”

“ It is obvious that the arc of contact taken to calculate the belt power must be the least that exists on either the driving or the driven pulley, because when the belt slips it ceases to transmit the full amount of the power it receives, the remainder being expended in the friction caused by the belt slipping over the pulley. ”

“ From the construction, the rivets joining the pieces forming the belt do not come into contact with the surfaces of the pulley, and from the tension of the belt causing it to wedge into the sides of the pulley groove, the driving power is greater than that simply due to the area of contact and the tension of the belt. ”

“ Another rule is, that at a velocity of 1000 ft. per min. each inch of breadth of belt should transmit 21/2 horse-power on metal pulleys, or 5 on wooden ones, on which the adhesion is greater. Adhesion may also be increased by covering the pulleys with leather or india-rubber. Both rules assume that the belt is of ample strength. One horse-power would be transmitted by a belt running 1000 ft. per min. with a pull of 33 lb. A good single belt should not break with a much less strain than 1000 lb. per inch of breadth, and should stand about 1/10 as much as a working strain. ”

“ The lace should be drawn sufficiently tight to bring the ends of the belt firmly together, and should be laced with an even tension throughout, and for a belt doing heavy duty should have its ends tied in a knot at the back, and in the middle of the belt. ”

“ The reason is that the load was all taken off the inside half of the belt by point slipping, thereby making the inside of the belt too long and putting all the load on the outside. The outside will continue to do all the work until it stretches enough to bring the inside back into service again. ”

“ Ultimate strength of ordinary leather belting = 3086 lb. per square inch. Belts vary from 3∕16 in. to 1⁄4in. thick, average 7∕32 in.
Power of Single Leather Belts.
To calculate the power of single leather belts, the following formula may be used: Let HP = actual horse-power. W = width of belt. F = driving force. T = working tension from 70 to 150 lb. V = velocity of belt in feet per minute.
Example:—A 10-inch belt running 2500 feet per minute, what horse-power will it transmit? Assuming the working tension to be 100 lb.,
[179] ”

“ A cemented and pegged joint is the strongest made, and it preserves a more equal tension throughout the belt than any other, while the belt is strong, since the hole for the pegs may be pierced with an awl, which does not remove any leather from the belt, as is the case with punched holes. ”

“ Next in importance is to buy a belt that has already been filled with some good waterproof dressing. It is quite likely that to buy a belt that has been filled means to buy one that perhaps has some bad leather in it that would be seen in a dry oak tan belt, and also that the adhesive power of the filled belt is not quite equal to the dry one ”

“ The object of this chapter is not to say how belts are made, but to impress upon the minds of belt users that to get the best results, belts, like all good servants, must be well cared for, and all responsibility should rest with one man, just as with your engine or any high-priced machine. ”

“ For reversing by belt gear, see Section 74. Gut bands (round) are worked over V-grooved pulleys; see Rope Gearing, Section 66. Belts may be kept tight by tightening pulleys, see No. 1207. For round belts, see Rope Gearing, Section 66. V-belts are occasionally used, formed of thicknesses of leather riveted together, cut to a V-section, and worked over V-grooved pulleys.
Section 4.—BALL-AND-SOCKET JOINTS. 30. Universal hinge. The arm can be fixed in any required position by tightening the gland. Useful for stands for articles to be exhibited in any position, telescopes, &c. ”

“ There is not one establishment in one hundred that does not leave the care and tightening of the belts to the judgment of the individual who runs the machine, although it is well known to all who have given any study to the subject that the most skilled machinist cannot properly tighten a belt without the use of belt clamps fitted with spring balances to properly register the tension. ”

“ When a belt envelops two pulleys that are at a right angle to each other, two guide pulleys are needed in order that the belt may, in passing to each pulley, move in the same plane as the pulley rotates in, and the belt is in this case given what is termed a quarter twist. ”

“ One long belt does the business. Shoe strings make the best belting—won’t stretch nor slip. Use shade poles one inch in diameter, bore hole in center of wheel one inch, make a tight fit. Use shade ends for bearings. They are cheap and give good service. To make ball bearings and have very little friction, take a steel ball such as is used in bicycles, imbed it in the wood, place the socket over it, screw it down, put in your shade end and you have a perfect bearing, especially so when you wish to make a heavy wax figure revolve.
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DESIGN SHOWING ELECTRICAL MILLINERY DISPLAY.—Softley. ”

“ When the direction of rotation of the driven pulley requires to be reversed from that of the driving pulley, the belt is crossed as in Fig. 2670. A crossed belt has a greater transmitting power than one uncrossed (or, as it is termed, than an “open belt”) because it envelops a greater arc of both pulleys’ circumference. This is often of great advantage where the two pulleys are of widely varying diameter, especially if the small pulley requires to transmit much power, and be of very small diameter. ”

“ When a belt connects two pulleys whose respective planes of revolution are at an angle one to the other, it is necessary that the centre line of the length of the belt shall approach the pulley in the plane of the pulley’s revolution, which is sufficient irrespective of the line of motion of the belt when receding from the pulley. ”

“ A belt tends to move towards that part of a pulley whose radius is greatest; pulleys for belts, therefore, are slightly swelled in the middle, in order that the belt may remain on the pulley, unless forcibly shifted. A belt when in motion is shifted off a pulley, or from one pulley on to another of equal size alongside of it, by pressing against that part of the belt which is moving towards the pulley. ”

“ If a belt is put on too tight, it may pull so hard on the bearings as to heat and cause them to cut. It is easier not to put the belt on too tight at first and to relace it several times while it is stretching, than it is to repair a rough bearing. ”

“ With very large machines under test, it is inadvisable to use the above method as it is sometimes difficult to so adjust the pulleys and belt tension that the belt slip will be just right to make up for the difference in diameter of the pulleys, and very violent flapping of the belt results. ”

“ As the length of the belt is increased, the gross amount of stretch, under any given condition, increases, and hence the longer the belt, the greater the variation of velocity at first starting between the driven pulley and the driver. ”

“ With heavy belts, particular care should be taken to prevent any portion of the clothing being caught either by the moving belt or pulleys, as many serious accidents have resulted in the past from carelessness in regard to this important detail. The person handling the belt should, therefore, be sure of a firm footing, and when it is impossible to secure this, it is advisable to stop the engine and fit the belt around the engine pulley as well as possible by the aid of a rope looped around the belt. ”

“ Single-flanged pulley for horizontal driving.
25. Open belt gear; runs best as shown, with the slack half of the belt at top.
26. Crossed belt to reverse motion on the driven shaft. Also to obtain more grip for the belt than with open belts.
27. Mode of driving when the shafts are at right angles to one another.
28. Mode of driving with shafts at an obtuse angle, sometimes used instead of bevel wheels.
29. Arrangement adopted when the pulleys cannot be got in line with one another, or the shafts are too close together to drive well direct. Short belts seldom work well. ”

“ Endless leather belting was used to transmit the power from the motor to the counter-shaft, and from the latter to the driving-wheels, which were the front pair. A vertical idler-pulley was mounted in a frame over the belt from motor to counter-shaft, terminating in a vertical screw and hand-wheel for tightening the belt to increase speed, or the reverse to lower speed. ”

“ Lacing is not stronger in proportion as it is heavy. If it is heavy and clumsy it gets strained in going round the pulley, and soon gives out. The ideal way to lace a belt is to make it as nearly like the rest of the belt as possible, so that it will go over the pulleys without a jar. The ends of the belt should be cut off square with a try square, and a small punch used for making holes. Holes should be equally spaced, and outside ones not so near the edge as to tear out. ”

“ Self-reversing gear, with one belt, two fast and one loose pulleys. The large spur wheel is driven from the bevil gear, and carries the weighted lever past the vertical position by a stop on the face-plate or disc, when it falls over and reverses the belt fork. ”

“ When the edge gets a trifle dull, use the small steel on both sides of the edge; first wet the steel with the lips, it makes a much better edge. For the benefit of beginners who may attempt to splice a belt for the first time, do not use a glue that will not allow you to remove the clamps and put on the full load in forty-five minutes after the glue has been applied and well rubbed down. The time given here applies only to clean belts that are absolutely free from all oils, and does not include old oil-soaked leather that no glue will ever dry on. ”

“ We have not stopped at flat link belting, but have turned our attention to manufacturing round solid leather link belting, and believe that we have almost attained perfection in that line. As the illustrations clearly show, there is quite a demand for inch and upward solid round belting, and the difficulty always has been to join such a belt together. All steel hooks, etc., do not seem to satisfy. This, our new invention, is so simple that it hardly needs explanation. A belt of this kind can be taken apart in a short time, and shortened or lengthened at pleasure. ”

“ CENTRAL BAR NICKEL BUCKLES ea. $.10; doz. $1.10
STANDARD BELT BUCKLES—brass or nickel finish for belt widths of 1′′ (the size recommended for the standard 12-strand belt) . 11⁄4′′, and 11⁄2′′ ea. $.07; doz. ”

“ Now if you know the circumference of your fly wheel, the number of revolutions your engine is making and the width of belt, you can figure very nearly the amount of power you can supply without slipping your belt. For instance, we will say your fly wheel is 40 inches in diameter or 10.5 feet nearly in circumference and your engine was running 225 revolutions a minute, your belt would be traveling 225 x 10.5 feet = 2362.5 feet or very nearly 2400 ft. ”

“ Adjustable centre pin, traversed by a screw, and fixed after adjustment by a nut and washer.
1953. Fine screw adjustment for any movable part.
1954. Fine screw adjustment for a radial arm.
1955. Division plate, with differential dividing on its opposite faces.
Belts, bands, &c., are adjusted by corresponding series of holes and laces, screws or rivets to fit them.
Section 3.—BELT GEARING. (See also p. 12.)
1956. Fast and loose pulleys; the fast pulley is larger in diameter than the loose pulley, to allow the belt to run slack when running idle.
1957. Round rubber belt gear. ”

“ Then take out the screw at the right hand side of the machine part and slip off the upper belt wheel. This upper belt wheel, the belt, the lower belt wheel, and the iron framework of the machine are all that will be needed for the lathe, and the rest you may discard, or put away in the “handy” pile for some future construction. The lower belt wheel is of course fastened to the frame, so that does not need to be disturbed. ”

“ In using belts care must be taken in shifting the belts to throw off one before attempting to put the other into operation, or broken belts and perhaps worse accidents may result. Belt driving is wonderfully smooth and quiet in action, and commendable from this point, but unless very carefully looked after liable to give trouble by undue slipping and breaking. ”