Budynas-Nisbett:Shigley's Ill.Design of Mechanical 13.Gears-General T©The McGraw-Hill 65 Mechanical Engineering Elements Companies,2008 Design,Eighth Edition 656 Mechanical Engineering Design Figure 13-5 Top land Nomenclature of spurgear teeth. Face wid由h Addendum circle Circular pitch Flank Tooth Pitch circle thickness Width of space Bottom land Clearance Fillet radius Dedendum Clearance circle circle The module m is the ratio of the pitch diameter to the number of teeth.The cus- tomary unit of length used is the millimeter.The module is the index of tooth size in SI. The diametral pitch P is the ratio of the number of teeth on the gear to the pitch diameter.Thus,it is the reciprocal of the module.Since diametral pitch is used only with U.S.units,it is expressed as teeth per inch. The addendum a is the radial distance between the top land and the pitch circle. The dedendum b is the radial distance from the bottom land to the pitch circle.The whole depth h,is the sum of the addendum and the dedendum. The clearance circle is a circle that is tangent to the addendum circle of the mat- ing gear.The clearance c is the amount by which the dedendum in a given gear exceeds the addendum of its mating gear.The backlash is the amount by which the width of a tooth space exceeds the thickness of the engaging tooth measured on the pitch circles. You should prove for yourself the validity of the following useful relations: P= d (13-1) d m二 (13-21 πd P=N =πm (13-3) pP=π (13-4) where P=diametral pitch,teeth per inch N=number of teeth d=pitch diameter,in m=module,mm d=pitch diameter,mm p circular pitchBudynas−Nisbett: Shigley’s Mechanical Engineering Design, Eighth Edition III. Design of Mechanical Elements 13. Gears — General © The McGraw−Hill 655 Companies, 2008 656 Mechanical Engineering Design Addendum Dedendum Clearance Bottom land Fillet radius Dedendum circle Clearance circle Tooth thickness Face width Width of space Face Top land Addendum circle Pitch circle Flank Circular pitch Figure 13–5 Nomenclature of spur-gear teeth. The module m is the ratio of the pitch diameter to the number of teeth. The cus￾tomary unit of length used is the millimeter. The module is the index of tooth size in SI. The diametral pitch P is the ratio of the number of teeth on the gear to the pitch diameter. Thus, it is the reciprocal of the module. Since diametral pitch is used only with U.S. units, it is expressed as teeth per inch. The addendum a is the radial distance between the top land and the pitch circle. The dedendum b is the radial distance from the bottom land to the pitch circle. The whole depth ht is the sum of the addendum and the dedendum. The clearance circle is a circle that is tangent to the addendum circle of the mat￾ing gear. The clearance c is the amount by which the dedendum in a given gear exceeds the addendum of its mating gear. The backlash is the amount by which the width of a tooth space exceeds the thickness of the engaging tooth measured on the pitch circles. You should prove for yourself the validity of the following useful relations: P = N d (13–1) m = d N (13–2) p = πd N = πm (13–3) pP = π (13–4) where P = diametral pitch, teeth per inch N = number of teeth d = pitch diameter, in m = module, mm d = pitch diameter, mm p = circular pitch