SDP/SI Introduction - Equivalence of American and Japanese Symbols

T-16 Table 1-4 (Cont.) Equivalence of American and Japanese Symbols 1.3.3 Terminology Terms used in metric gearing are identical or are parallel to those used for inch gearing. The one major exception is that metric gears are based upon the module, which for reference may be considered as the inversion of a metric unit diametral pitch. Terminology will be appropriately introduced and defined throughout the text. There are some terminology difficulties with a few of the descriptive words used by the Japanese JIS standards when translated into English. One particular example is the Japanese use of the term "radial" to describe measures such as what Americans term circular pitch. This also crops up with contact ratio. What Americans refer to as contact ratio in the plane of rotation, the Japanese equivalent is called "radial contact ratio". This can be both confusing and annoying. Therefore, since this technical section is being used outside Japan, and the American term is more realistically descriptive, in this text we will use the American term "circular" where it is meaningful. However, the applicable Japanese symbol will be used. Other examples of giving preference to the American terminology will be identified where it occurs. 1.3.4 Conversion For those wishing to ease themselves into working with metric gears by looking at them in terms of familiar inch gearing relationships and mathematics, Table 1-5 is offered as a means to make a quick comparison. Table 1-5 Spur Gear Design Formulas * All linear dimensions in millimeters Continued on following page Symbols per Table 1-4 whole depth contact ratio number of teeth, pinion number of threads in worm axial pitch base pitch circular pitch normal circular pitch pitch radius, pinion base circle radius, pinion fillet radius outside radius, pinion tooth thickness, and for general use, for tolerance American Symbol h_t m_p n n_w p_a p_b p_c p_cn r r_b r_f r_o t Japanese Symbol h e z₁ z_w p_x p_b p p_n r r_b r_f r_a s Nomenclature American Symbol y_c g q l ^mn_f ^foY w invf Japanese Symbol d g a ^awb inv a Lewis factor, circular pitch pitch angle, bevel gear rotation angle, general lead angle, worm gearing mean value gear stage velocity ratio pressure angle operating pressure angle helix angle (b_b=base helix angle; b_w= operating helix angle) angular velocity involute function Nomenclature Use This Formula* D = mN D p_c = mp = ––––p N 25.4 m = –––––– P_d D N = ––– m a = m From Known Module Module Diametral Pitch Module and Pitch Diameter Module To Obtain Pitch Diameter Circular Pitch Module Number of Teeth Addendum