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Minimum Number of Teeth on the Pinion in Order to Avoid Interference
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The phenomenon when the tip of a tooth undercuts the root on its mating gear is known as interference. The minimum number of teeth on the pinion which will mesh with any gear (also rack) without interference is 17 or it may be determined by,

Z1=2(sinα)2 where α is pressure angle of gear and Z1= no. of teeth on the pinion

Design Criteria for Gears (Also refer PSG Design Data Book)

Parameter Spur Gear Helical Gear
Strength Criteria - Design m1.263[Mt]y[σb]φmZ1
PSG 8.13A
mn1.15cosβ3[Mt]yv[σbφmZ1
PSG 8.13A
Strength Criteria - Checking Fs=πybm[σb]
FsFLD or Fd
FLD=Ft×Cv
PSG 8.50

OR

σb=i±1amby[Mt][σb]
PSG 8.13A
Fs=πybmn[σb]
FsFLD or Fd
FLD=Ft×Cv
PSG 8.50

OR

σb=0.7i±1abmnyv[Mt][σb]
PSG 8.13A
Wear Criteria - Design Find module using
Fw=FLD Or
d1Qkb=Ft×Cv
PSG 8.51
Find module using
Fw=FLD Or
d1Qkbcosβ2=Ft×Cv
PSG 8.51
Wear Critera - Checking Fw=d1Qkb
FwFLD
PSG 8.51
Fw=d1Qkbcosβ2,FwFLD
PSG 8.51
Surface / Contact Stresses - Design a(i±1)3(0.74[σc])2E[Mt]iφ
Find module using a=m2(Z1+Z2)
PSG 8.13
a(i±1)3(0.7[σc])2E[Mt]iφ
Find a. Find module using
a=mncosβ(Z1+Z2)2
PSG 8.13
Surface / Contact Stresses - Checking σc=0.74i±1ai±1ibE[Mt][σc] PSG 8.13 σc=0.7i±1ai±1ibE[Mt] [σc],
PSG 8.13
Parameter Bevel Gear Worm Gear
Strength Criteria - Design mav1.28
3[Mt]yv[σb]φmZ1
PSG 8.13A
mx1.243[Mt]zqyv[σb]
PSG 8.44
Strength Criteria - Checking Fs=[σb]bπyv(1bR)m
FsFLD or Fd
FLD=CvNsfKmFt
PSG 8.52

OR

σb=Ri2+1[Mt](R0.5b)2bmyv1cosα[σb]
PSG 8.13A
Fs=πybm[σb]
FsFLD or Fd
FLD=Ft×Cv,Cv=
(6+vmg6)
PSG 8.25

OR

σb=1.9[Mt]m3xqzyv[σb]
PSG 8.44
Wear - Design Find module using
Fw=FLD Or
d1Qkbcosδ1=Ft×Cv
PSG 8. 52
Find module using
Fw=FLD( Fd ) Or
Dgbkw=Ft×(6+vmg6)
PSG 8.52
Wear - Checking Fw=d1Qkbcosδ1,FwFLD
PSG 8.52
Fw=Dgbkw
FwFLD(Fd)
PSG 8.52
Surface / Contact Stresses - Design Rφyi2+13(0.72(φy0.5)[σc])
Find R.
Find module using formulae in Table 31,
PSG 8.38
a=(zq+1)3(540q[σc])2[Mt]
-- 8.44
Find 'a'. Find module using formulae on
PSG 8.43
Surface / Contact Stresses - Checking σC=0.72(R0.5b)(i2±1)3ibE[Mt][σc]
PSG 8.13
σc=(540zq)(zq+1)3a[Mt][σC]
PSG 8.44
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