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ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMRT Handbook of Timing Belts, Pulleys, Chains and SprocketsThe Technical Section of this catalog is the result of close cooperation of StockDrive Products / Sterling Instrument staff with experts in the fields of powertransmission design and manufacturing. We wish, therefore, to recognize thecontribution of the following company and individuals:Inch0The Gates Rubber Company, that provided the material contained in their publication 17183.12Staff of Stock Drive Products / Sterling Instrument.No part of this publication may be reproduced in any form or by any means without the priorwritten permission of the Company. This does not cover material which was attributed toanother publication.3456789101112131415AT-01
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMTABLE OF CONTENTSPAGERSECTION 1 INTRODUCTION .T-3SECTION 2 GATES POWERGRIP GT 3 BELT DRIVES .T-4SECTION 3 COMPARISON GRAPHS .T-6SECTION 4 DRIVE COMPARATIVE STUDIES .T-84.14.24.34.4Durability .T-8Tooth Jump Resistance .T-8Noise .T-9Positioning Accuracy .T-9T123SECTION 5 DIFFERENT BELT CONFIGURATIONS .T-10Double-Sided Twin Power Belt Drives .T-10Long Length Timing Belt Stock .T-104SECTION 6 BELT CONSTRUCTION .T-1055.15.26.16.26.36.4Characteristics Of Reinforcing Fibers .T-11Cord Twist And Its Effect On The Drive .T-12Factors Contributing To Side Travel .T-13Characteristics Of Belt Body Materials .T-146SECTION 7 BELT TOOTH PROFILES .T-157SECTION 8 PULLEY PITCH AND OUTSIDE DIAMETERS .T-16SECTION 9 DESIGN AND INSTALLATION SUGGESTIONS .T-229.19.29.39.49.59.69.79.89.9Low-Speed Operation .T-23High-Speed Operation .T-23Smooth Running .T-24Drive Noise .T-24Static Conductivity .T-24Operating Environments .T-25Belt Tracking .T-26Pulley Flanging .T-27Registration .T-28SECTION 10 BELT TENSIONING .T-2910.110.2What Is Proper Installation Tension .T-29Making Measurements .T-31SECTION 11 DRIVE ALIGNMENT .T-3211.111.2Angular And Parallel .T-32Practical Tips .T-33891011121314SECTION 12 INSTALLATION AND TAKE-UP .T-3312.1Installation Allowance .T-33T-115A
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMRT1234512.212.312.4Belt Installation .T-33Belt Take-up .T-34Fixed Center Drives .T-34SECTION 13 IDLER USAGE .T-3513.113.213.313.413.513.6Inside/Outside .T-35Tight Side/Slack Side .T-35Idler Placement .T-35Spring-Loaded Idlers .T-35Size Recommendations .T-35Specifying Shaft Locations In Multipoint Drive Layouts .T-36SECTION 14 BELT PULL AND BEARING LOADS .T-3714.114.214.314.4Motion Transfer Drives .T-38Power Transmission Drives .T-38Registration Drives .T-39Bearing Load Calculations .T-39SECTION 15 HANDLING AND STORAGE .T-40SECTION 16 STANDARDS APPLICABLE TO BELTS .T-40678910SECTION 17 STANDARDS APPLICABLE TO PULLEYS AND FLANGES .T-4217.117.217.317.4Pulley Tolerances .T-43Pulley Materials .T-46Flange Design And Face Width Guidelines .T-46Guidelines For PowerGrip GT 3 Flange Design .T-47SECTION 18 DOUBLE-SIDED TWIN POWER BELT TOLERANCES .T-48SECTION 19 LONG LENGTH TIMING BELT STOCK SPECIFICATIONS .T-49SECTION 20 DESIGN AIDS ON INTERNET (www.sdp-si.com) .T-50SECTION 21 DRIVE RATIO TABLES .T-51SECTION 22 CENTER DISTANCE FORMULAS re And Basic Equations .T-58Exact Center Distance Determination – Unequal Pulleys .T-58Exact Center Distance Determination – Equal Pulleys .T-59Approximate Center Distance Determination .T-59Number Of Teeth In Mesh (TIM) .T-59Determination Of Belt Size For Given Pulleys And Center Distance.T-60SECTION 23 CENTER DISTANCE FACTOR TABLES . T-60SECTION 24 TIMING BELT DRIVE SELECTION PROCEDURE . T-61LIST OF TABLES . T-83LIST OF FIGURES . T-85T-2
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMRSECTION 1 INTRODUCTIONTiming belts are parts of synchronous drives which represent an important category of drives.Characteristically, these drives employ the positive engagement of two sets of meshing teeth. Hence, they donot slip and there is no relative motion between the two elements in mesh.Due to this feature, different parts of the drive will maintain a constant speed ratio or even a permanentrelative position. This is extremely important in applications such as automatic machinery in which a definitemotion sequence and/or indexing is involved.The positive nature of these drives makes them capable of transmitting large torques and withstandinglarge accelerations.Belt drives are particularly useful in applications where layout flexibility is important. They enable thedesigner to place components in more advantageous locations at larger distances without paying a pricepenalty. Motors, which are usually the largest heat source, can be placed away from the rest of the mechanism.Achieving this with a gear train would represent an expensive solution.Timing belts are basically flat belts with a series of evenly spaced teeth on the inside circumference,thereby combining the advantages of the flat belt with the positive grip features of chains and gears.There is no slippage or creep as with plain flat belts. Required belt tension is low, therefore producingvery small bearing loads. Synchronous belts will not stretch and do not require lubrication. Speed is transmitteduniformly because there is no chordal rise and fall of the pitch line as in the case of roller chains.The tooth profile of most commonly known synchronous belts is of trapezoidal shape with sides beingstraight lines which generate an involute, similar to that of a spur gear tooth. As a result, the profile of the pulleyteeth is involute. Unlike the spur gear, however, the outside diameter of a timing pulley is smaller than its pitchdiameter, thus creating an imaginary pitch diameter which is larger than the pulley itself. This is illustrated inFigure 1. Backlash between pulley and belt teeth is negligible.Pitch (circular pitch)Pitch (circular pitch)eOutsidterDiameTrapezodialTooth Profile1234567Belt Pitch LineBelt Pitch LinePitchDiameterTPitchDiameterPulley Pitch CircleeOutsidterDiameCurvilinear ToothProfileSprocket Pitch Circle8910Fig. 1 Pulley and Belt GeometryThe trapezoidal shape timing belt was superseded by a curvilinear tooth profile which exhibited somedesirable and superior qualities. Advantages of this type of drive are as follows: Proportionally deeper tooth; hence tooth jumping or loss of relative position is less probable. Lighter construction, with correspondingly smaller centrifugal loss. Smaller unit pressure on the tooth since area of contact is larger. Greater shear strength due to larger tooth cross section. Lower cost since a narrower belt will handle larger load. Energy efficient, particularly if replacing a "V" belt drive which incurs energy losses due to slippage. Installation tension is small, therefore, light bearing loads.11121314NOTE: Credit for portions of this technical section are given to: Gates Rubber Co., Sales Engineering Dept., RubberManufacturers Association (RMA), International Organization for Standardization (ISO).T-315A
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMRTension MemberT12CurvilinearTrapezoidalFig. 2 Stress Pattern in Belts345678910In Figure 2, the photoelastic pattern shows the stress distribution within teeth of different geometry.There is a definite stress concentration near the root of the trapezoidal belt tooth, with very low strainselsewhere. For the curvilinear tooth, there is a uniform, nearly constant, strain distribution across the belt.The load is largest in the direction of the tension member to which it is transferred.Because of their superior load carrying capabilities, the curvilinear belts are marketed under the nameof Gates' HTD drives. This is an abbreviation of High Torque Drives.As a result of continuous research, a newer version of the curvilinear technology was developed byGates, which was designated as Gates' PowerGrip GT 3 belt drives.SECTION 2 GATES POWERGRIP GT 3 BELT DRIVESThe PowerGrip GT3 Belt Drive System is an advance in product design over the Gates' older, standardHTD system. The PowerGrip GT3 System, featuring a modified curvilinear belt tooth profile, provides timingand indexing accuracy superior to the conventional PowerGrip Trapezoidal Belt System. Plus, PowerGrip GT3Belts have a higher capacity and longer belt life than trapezoidal belts.It's difficult to make a true quantitative comparison between the backlash of a trapezoidal tooth drive andPowerGrip GT3 drive due to the difference in "pulley to belt tooth" fit (see Figure 3). Trapezoidal belts contactthe pulley in the root radius-upper flank area only, while the PowerGrip GT3 system permits full flank contact.The main stress line in a trapezoidal tooth timing belt is at the base of the teeth. During operation, thisstress greatly reduces belt life. The PowerGrip GT3 system overcomes this condition with its complete toothflank contact which eliminates the tooth stress line area. This greatly increases belt life and prevents toothdistortion caused by drive torque. In addition, the conventional timing belt has a chordal effect as it wrapssmall pulleys. This is significantly reduced in the PowerGrip GT3 system because there is full tooth support111213PowerGrip GT 3 BeltTooth/Groove ContactPowerGrip HTD BeltTooth/Groove ContactPowerGrip Trapezoidal BeltTooth/Groove ContactFig. 3 Comparison of Different Tooth Profiles1415AT-4
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMalong the pulley. Full support improves meshing, reduces vibration and minimizes tooth deformation.On drives using a low installation tension, small pulleys, and light loads, the backlash of the PowerGripGT3 system will be slightly better than the trapezoidal timing belt system. However, with increased tensionand/or loads and/or pulley sizes, the performance of the PowerGrip GT3 system becomes significantly betterthan the trapezoidal timing belt system.The PowerGrip GT3 system is an extension of the HTD system with greater load-carrying capacity.HTD was developed for high torque drive applications, but is not acceptable for most precision indexing orregistration applications. The HTD design requires substantial belt tooth to pulley groove clearance (backlash)to perform.As smaller diameter pulleys are used, the clearance required to operate properly is increased. HTD driveclearance, using small diameter pulleys, is approximately four times greater than an equivalent GT3 timing beltdrive.The PowerGrip GT3 system's deep tooth design increases the contact area which provides improvedresistance to ratcheting. The modified curvilinear teeth enter and exit the pulley grooves cleanly, resultingin reduced vibration. This tooth profile design results in parallel contact with the groove and eliminatesstress concentrations and tooth deformation under load. The PowerGrip GT3 design improves registrationcharacteristics and maintains high torque carrying capability.PowerGrip GT3 belts are currently available in 2 mm, 3 mm, 5 mm, 8 mm and 14 mm pitches. Specificadvantages of the PowerGrip GT3 system can be summarized as follows: Longer belt lifeThe strong fiberglass tensile cords wrapped in a durable neoprene body provide the flexibility neededfor increased service life. The deep tooth profile provides superior load-carrying strength and greatlyreduces ratcheting when used with pulleys provided by a licensed supplier. Precision registrationPowerGrip GT3 belts provide timing and synchronization accuracy that make for flawless registration,with no loss of torque carrying capacity. Increased load-carrying capacityLoad capacities far exceed HTD and trapezoidal belt capabilities making PowerGrip GT3 belts the choicefor accurate registration, heavy loads and small pulleys. Quieter operationThe PowerGrip GT3 belt's specially engineered teeth mesh cleanly with pulley grooves to reduce noiseand vibration. Clean meshing and reduced belt width result in significant noise reduction when comparedto Trapezoidal and HTD belts. Precise positioningPowerGrip GT3 belts are specifically designed for applications where precision is critical, such ascomputer printers and plotters, laboratory equipment and machine tools.Some of the many applications of PowerGrip GT3 belts are: data storage equipment printers machine tools floor care equipment hand power tools money handling equipment postage handling equipment medical diagnostic equipment DC stepper/servo applications sewing machines food processors vacuum cleaners centrifuges automated teller machines ticket dispensers plotters copiers robotics equipment vending equipment office equipmentRT123456789101112131415T-5A
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMSECTION 3 COMPARISON GRAPHSTIn order to provide comparison of performances of different pitch drives, several graphs have beendeveloped. Figure 4 shows numerical values, plotted in logarithmic scale, of Rated Horsepower vs. Speed(rpm) of faster shaft.700R14 mmGT3110XH5H7Rated Horsepower5 mmGT36LT10913 mmGT38XLT52 601,7502,500Speed (rpm) of Faster Shaft15A5,0004,0003,45020,0001410,000.0113Fig. 4 Comparative Belt Pitch Selection GuideXXHMXLXLLHXHXXH410038 mmGT3 .080" pitch .200" pitch .375" pitch .500" pitch .875" pitch 1.250" pitch2
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMFigure 5 shows an illustrative graph representation of horsepower ratings over a wide speed range ofthe belt types commonly used. The graph assumes that belt widths and pulley diameters have been chosensuch that they provide realistic comparison of product capability.RT1Rated Horsepower6254332410124681012141618520Speed (rpm)Fig. 5 Horsepower Ratings at High Speed67Figure 6 provides a comparison of the rated torque carrying capabilities of synchronous belts, on smalldiameter pulleys at low speeds. The pulley diameters and belt widths represent a realistic comparison.8910Rated 00500700131000Speed (rpm)14Fig. 6 Horsepower Ratings at Low Speed15T-7A
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COM24.1 DurabilityThe greatly increased durability of the PowerGrip GT3 design has resulted in power capacities far abovethose quoted for similar size belts of previous designs. The resulting small drive packages will increase designflexibility, space utilization and cost effectiveness.35Performance Ratio (%)42008100500141.2.1005005 mm HTD5mm GT3TEST CONDITIONS: Speed 2300 rpmPower 3.35 lbf in./mm widthPulleys: Driver 20 groovesDriven 20 groovesTooth Jump Torque (lbf in.)Ratcheting resistance during high start-up torques.Reduced bearing loads, particularly in fixed-center drives. Lower average tensions can be usedwithout encountering tooth jump at the low tension end of the tolerance ranges.Reduced system losses result from lower pre-tensioning, with less potential for tooth jumping.102 mm PowerGrip GT3 vs MXL82 mm GT36MXL4201234Installed Tension (lbf)TEST CONDITIONS:Speed 1130 rpmBelt Width 4.8 mmPulleys: Driver 20 groovesDriven 20 grooves53 mm PowerGrip GT3 vs 3 mm HTD60504030201003 mm GT33 mm HTD246810Installed Tension (lbf)TEST CONDITIONS:Speed 750 rpmBelt Width 6 mmPulleys: Driver 30 groovesDriven 30 grooves4505 mm PowerGrip GT3 vs 5 mm HTD375300T-85 mm GT35 mm HTD2251507501530456075Installed Tension (lbf)TEST CONDITIONS:Speed 2300 rpmBelt Width 15 mmPulleys: Driver 20 groovesDriven 20 groovesFig. 8 Comparison of Tooth Jump Torques for Various Belts15A150The very significant improvement in tooth jump resistance of PowerGrip GT3 when compared to similarbelts has several important advantages.3.135 mm HTD Versus 5 mm PowerGrip GT3Test Stopped ––– 4.2 Tooth Jump Resistance1012200Fig. 7 Comparison of Performance Ratios for Various Belts911Test Stopped ––– 1503 mm HTD3 mm GT3TEST CONDITIONS: Speed 6000 rpmPower 1.00 lbf in./mm widthPulleys: Driver 20 groovesDriven 20 grooves673 mm HTD Versus 3 mm PowerGrip GT3Tooth Jump Torque (lbf in.)1The development of the PowerGrip GT3 belt has produced an impressive range of enhanced propertiesand subsequent design opportunities for engineers.Comparative studies, shown in Figures 7 through 10, allow designers to make quantitative assessmentsand to highlight the most significant improvements and design opportunities. Particularly significant pointsfrom the comparative studies follow:Performance Ratio (%)TSECTION 4 DRIVE COMPARATIVE STUDIESTooth Jump Torque (lbf in.)R
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COM4.3 NoiseRThe smoother meshing action of the PowerGrip GT3 belt, with its optimized design, produces significantlylower noise levels when compared with other similar sized belt types operating under similar speeds andtensions. These improvements are enhanced by the fact that narrower belts can be used due to increasedpower capacities.T3 mm PowerGrip GT3 vs 3 mm HTD1101001009090803 mm HTD7060Noise (dBA)Noise (dBA)1105 mm PowerGrip GT3 vs 5 mm HTD125 mm HTD807035 mm GT3603 mm GT345050401000 1500 2000 2500 3000 3500 4000 4500Speed (rpm)401000 1500 2000 2500 3000 3500 4000 4500Speed (rpm)Belt:No. of teeth 118Width 30 mmPulleys: Driver 20 groovesDriven 20 groovesMicrophone location midway betweenthe pulleys, 100 mm from the belt edge.Belt:No. of teeth 188Width 15 mmPulleys: Driver 26 groovesDriven 26 groovesMicrophone location midway betweenthe pulleys, 100 mm from the belt edge.56Fig. 9 Comparison of Noise Levels for Various Belts4.4 Positioning Accuracy7The PowerGrip HTD belt tooth forms were primarily designed to transmit high torque loads. Thisrequirement increased tooth to groove clearances which resulted in increased backlash when compared withthe original trapezoidal designs.PowerGrip GT3 has reversed this problem with power capacities now exceeding those of PowerGrip HTDwhile giving equivalent or higher levels of positional accuracy than trapezoidal timing belts.8.002.001010.003Positioning Error (in.)Positioning Error (in.).0032 mm GT3MXLAPPLICATION: Motion TransferBelt: No. of teeth 126Width 8 mmPulleys: Driver 12 groovesDriven 40 groovesInstalled tension 1.8 lbfMotor 200 steps/cycle.00211.001093 mm GT33 mm HTDAPPLICATION: Motion TransferBelt: No. of teeth 92Width 6 mmPulleys: Driver 20 groovesDriven 20 groovesInstalled tension 6.6 lbfMotor 200 steps/cycleFig. 10 Comparison of Positioning Errors of Various Belts12131415T-9A
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMRSECTION 5 DIFFERENT BELT CONFIGURATIONS5.1 Double-Sided Twin Power Belt DrivesT12345678910111213Timing belts are also available in double-sided designs, which offer an infinite number of new designpossibilities on computer equipment, business machines, office equipment, textile machines and similar lightduty applications. Belts with driving teeth on both sides make it possible to change the direction of rotation ofone or more synchronized pulleys with only one belt. The inside and outside teeth are identical as to size andpitch and operate on standard pitch diameter pulleys.If the belts have nylon facing on both sides, then the same design parameters can be used for the driveson both sides of the belt. In case the outside teeth do not have nylon facing, the horsepower rating of theoutside teeth is only 45% of the total load.Pulley BFor example: assuming the drive pulleyOutside TeethPulley A.45 hpInside Teethand belt are capable of transmitting 1.55 hphorsepower, 0.55 hp can be transmitted fromDriverthe inside teeth of the pulley (A), and 0.45 hpOutput1 hpcan be transmitted by the outside teeth topulley (B) for a total of 1 hp, the rated capacity ––––––––––––– Belt Directionof the driver pulley.Fig. 11 Double-Sided Timing Belt5.2 Long Length Timing Belt StockThese belts are an excellent solution for drivesthat require belt lengths longer than those produced inconventional endless form. Long length belting has thesame basic construction as conventional timing belts.These belts are usually produced by spiral cut of largediameter endless belts. These belts are creatively used in: reciprocating carriage drives rack and pinion drives large plottersAn example of application is shown in Figure 13. Acomplete timing belt and a timing belt segment reducevibration and chatter in this oscillating drive for a surfacegrinder.SECTION 6 BELT CONSTRUCTIONFig. 12 Timing Belt StockFig. 13 Example of Timing Belt Stock UseThe load-carrying elements ofthe belts are the tension membersbuilt into the belts (see Figure 14).These tension members can bemade of:1. Spirally wound steel wire.2. Wound glass fibers.3. Polyester cords.4. Kevlar.Trapezoidal14Fig. 14 Belt Construction15ACurvilinearT-10
ITIMING BELTS, PULLEYS, CHAINS AND SPROCKETSPHONE: 516.328.3300 FAX: 516.326.8827 WWW.SDP-SI.COMThe tension members are embedded in neoprene or polyurethane. The neoprene teeth are protected by a nylonfabric facing which makes them wear resistant.The contributions of the construction members of these belts are as follows:1.2.3.4.Tensile Member – Provides high strength, excellent flex life and high resistance to elongation.Neoprene Backing – Strong neoprene bonded to the tensile member for protection against grime,oil and moisture. It also protects from frictional wear if idlers are used on theback of the belt.Neoprene Teeth – Shear-resistant neoprene compound is molded integrally with the neoprenebacking. Th
Drive Products / Sterling Instrument staff with experts in the fields of power transmission design and manufacturing. We wish, therefore, to recognize the contribution of the following company and individuals: The Gates Rubber Company, that provided the material contained in their publication 17183. Staff of Stock Drive Products / Sterling .
