POWER TRANSMISSION ELEMENTS AND MECHANISMS 



175 



CHART FOR FINDING V-BELT LENGTHS 



Diameter of Small Sheave 



Size of 

 ropes, in. 



32^16 



Min.diams. 

 recommended 



Permis- 

 sible 



Ra+io 



60- 

 59- 

 58- 

 57- 

 56- 

 55- 

 54- 

 53- 

 52- 



51- 

 50- 

 49- 

 48- 

 47- 

 46- 

 45- 

 44- 

 43- 

 42- 

 41- 

 40- 

 39- 

 38- 

 37- 

 36- 

 35- 

 34- 



Jl>- 

 32- 

 31- 

 30- 

 29- 

 28- 

 27- 

 26- 

 25- 

 24- 

 23- 

 22- 



21- 

 20- 

 19- 

 18- 

 17- 

 16- 

 'l5- 

 14- 

 13- 



12- 

 II - 

 10- 

 9- 

 8- 

 7- 

 6- 

 5- 

 4- 



3- 

 2- 

 I - 

 0- 



Given pitch diameter of the 

 small sheave, center distance, 

 and speed ratio : to find length 

 of V belt, place straightedge 

 on the given points of small 

 sheave diameter (right) and 

 center distance (left), and 

 note intersection with ratio 

 line (middle). Interpolate be- 

 tween diagonal belt length 

 lines to obtain desired length. 



Exam-pie: Dotted line drawn 

 between points representing 

 small sheave diameter of 15.65 

 in. and center distance 46 in. 

 intersects ratio line 2.6 at 

 diagonal line for 180 in. belt 

 length. 



The V-belt drive consists of 

 a driving and driven sheave, 

 grooved for a multiphcity of 

 belts of trapezoidal cross sec- 

 tion. Power is transmitted 

 by the wedging contact be- 

 tween the belts and grooves. 

 At maximum load, repeated 

 tests show an efficiency of 99 

 per cent and a co-efiicient of 

 friction of 1.5. V-belt drives 

 operate, therefore, with com- 

 paratively small tension on 

 the slack side, without slip- 

 page and with httle creep. 

 In figuring loads, it is usually 

 safe to take 1.5 times the 

 torque to get the total belt 

 pull. Manufacturer's ratings 

 must be consulted for selection 

 of number and size of belts for 

 given load conditions. 



A V-belt drive will usually 

 be well proportioned when 

 the center distance equals or 

 is slightly greater than the 

 large sheave diameter. On 

 small ratios, the sheaves may 

 be operated so closely to- 

 gether that the sheaves almost 

 touch each other. Maximum 

 center distance on J;^-in. belts 

 is 17 in., except on high ratios, 

 where 25 in. is permissible. 



In the accompanying chart, 

 the sheave diameters are the 

 pitch diameters, measured at 

 the mid-point of the trape- 

 zoidal section of the belt when 

 resting in the groove. 



