Machinery's Handbook, 31st Edition
2206 Gears and Gearing Efficiency is the torque ratio of a gear set divided by its gear ratio. Equivalent pitch radius is the radius of curvature of the pitch surface at the pitch point in a plane normal to the pitch line element. Face advance is the distance on the pitch circle that a gear tooth travels from the time pitch point contact is made at one end of the tooth until pitch point contact is made at the other end. Fillet radius is the radius of the concave portion of the tooth profile where it joins the bot tom of the tooth space. Fillet stress is the maximum tensile stress in the gear tooth fillet. Flank of tooth is the surface between the pitch circle and the bottom land, including the gear tooth fillet. Gear ratio is the ratio between the numbers of teeth in mating gears. Helical overlap is the effective face width of a helical gear divided by the gear axial pitch. Helix angle is the angle that a helical gear tooth makes with the gear axis at the pitch circle, unless specified otherwise. Hertz stress, see Contact stress . Highest point of single tooth contact (HPSTC) is the largest diameter on a spur gear at which a single tooth is in contact with the mating gear. Interference is the contact between mating teeth at some point other than along the line of action. Internal diameter is the diameter of a circle that coincides with the tops of the teeth of an internal gear. Internal gear is a gear with teeth on the inner cylindrical surface. Involute is the curve generally used as the profile of gear teeth. The curve is the path of a point on a straight line as it rolls along a convex base curve, usually a circle. Land The top land is the top surface of a gear tooth and the bottom land is the surface of the gear between the fillets of adjacent teeth. Lead is the axial advance of the helix in one complete turn, or the distance along its own axis on one revolution if the gear were free to move axially. Length of action is the distance on an involute line of action through which the point of contact moves during the action of the tooth profile. Line of action is the portion of the common tangent to the base cylinders along which con tact between mating involute teeth occurs. Lowest point of single tooth contact (LPSTC) is the smallest diameter on a spur gear at which a single tooth is in contact with its mating gear. Gear set contact stress is deter mined with a load placed on the pinion at this point. Module is the ratio of the pitch diameter to the number of teeth, normally the ratio of pitch diameter in mm to the number of teeth. Module in the inch system is the ratio of the pitch diameter in inches to the number of teeth. Normal plane is a plane normal to the tooth surfaces at a point of contact and perpendicu- lar to the pitch plane. Number of teeth is the number of teeth contained in a gear. Outside diameter is the diameter of the circle that contains the tops of the teeth of external gears. Pitch is the distance between similar, equally-spaced tooth surfaces in a given direction along a given curve or line. Pitch circle is the circle through the pitch point having its center at the gear axis. Pitch diameter is the diameter of the pitch circle. The operating pitch diameter is the pitch diameter at which the gear operates. Pitch plane is the plane parallel to the axial plane and tangent to the pitch surfaces in any pair of gears. In a single gear, the pitch plane may be any plane tangent to the pitch surfaces. Pitch point is the intersection between the axes of the line of centers and the line of action. Plane of rotation is any plane perpendicular to a gear axis.
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