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4. Calculate the Pitch-line velocity and Tooth bending stress
Calculate the Pitch Line velocity from: v = pi m Tp np / 60 and check ??? in the catalogue??? that it is acceptable. If not, repeat the calculation with different gears until an acceptable velocity is reached. Once an acceptable velocity is acheived the maximum bending stress must be calculated for both pinions and wheels, using

st = P / (v Kv f m Y),

where K = 6 / (6 + v), f is the face width, m the module and Y the Lewis form factor taken from the following table:
Number of teeth Lewis form factor Number of teeth Lewis form factorNumber of teeth Lewis form factorNumber of teeth Lewis form factorNumber of teeth Lewis form factor
12 0.230 17 0.285 22 0.320 34 0.367 75 0.423
13 0.243 18 0.293 24 0.331 38 0.377 100 0.436
14 0.255 19 0.30126 0.340 45 0.391 150 0.449
15 0.266 20 0.308 28 0.348 50 0.399 300 0.464
16 0.276 21 0.314 30 0.355 60 0.410 Rack 0.479

Choose a material for each gear that has the required strength using the catalogue or the following table of strengths and allowable stresses:-
Material, grade and condition Tensile strength, stt (MPa) Allowable stresses
Bending, stb(MPa) Surface, sts(MPa)
Nylon - 65 (20oC)
36 (100oC)		 12 -
Tuf nol-110 31 4
Cast Iron GRl 7 247 62 10
Aluminium Alloy HR1 5N - 90 3
Phosphor Bronze PB2 185 48 5
Steels
EN 8 - 08OM40 - 540 131 9
EN 8 - 08OM40 Induction Hardened 540 117 19
EN 24 - 817M40 -772 221 21
EN 24 - 817M40Induction Hardened 772 183 34
EN 32 - 045M10 - 494 117 10
EN 32 - 045M10 Case Hardened494 276 63
EN 36 - 655M13 Case Hardened 849 345 76
EN 58AM - 30S21 -540 138 12