T-153
17.1.4 Helix Angle Factor, Yb
Helix angle factor can be obtained from Equation (17-9).
b
When 0 £ b £ 30°, then Yb = 1 – ––––
ü
120
ï
ý
(17-9)
ï
When b > 30°, then Yb = 0.75
þ
12
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
110
120
RACK
12
1.420
1.451
1.489
1.516
1.537
1.553
1.567
1.578
1.588
1.596
1.603
1.609
1.614
1.619
1.623
1.627
1.630
1.634
1.636
1.642
1.646
1.701
15
1.481
1.519
1.547
1.567
1.584
1.597
1.609
1.618
1.626
1.633
1.639
1.645
1.649
1.654
1.657
1.661
1.664
1.667
1.672
1.676
1.731
20
1.557
1.584
1.605
1.622
1.635
1.646
1.656
1.664
1.671
1.677
1.682
1.687
1.691
1.695
1.699
1.702
1.705
1.710
1.714
1.769
25
1.612
1.633
1.649
1.663
1.674
1.683
1.691
1.698
1.704
1.710
1.714
1.719
1.723
1.726
1.729
1.732
1.737
1.742
1.797
30
1.654
1.670
1.684
1.695
1.704
1.712
1.719
1.725
1.731
1.735
1.740
1.743
1.747
1.750
1.753
1.758
1.762
1.817
35
1.687
1.700
1.711
1.721
1.729
1.736
1.742
1.747
1.752
1.756
1.760
1.764
1.767
1.770
1.775
1.779
1.834
40
1.714
1.725
1.734
1.742
1.749
1.755
1.761
1.765
1.770
1.773
1.777
1.780
1.783
1.788
1.792
1.847
45
1.736
1.745
1.753
1.760
1.766
1.772
1.777
1.781
1.785
1.788
1.791
1.794
1.799
1.804
1.859
50
1.755
1.763
1.770
1.776
1.781
1.786
1.790
1.794
1.798
1.801
1.804
1.809
1.813
1.868
55
1.771
1.778
1.784
1.789
1.794
1.798
1.802
1.806
1.809
1.812
1.817
1.821
1.876
60
1.785
1.791
1.796
1.801
1.805
1.809
1.813
1.816
1.819
1.824
1.828
1.883
65
1.797
1.802
1.807
1.811
1.815
1.819
1.822
1.825
1.830
1.834
1.889
70
1.808
1.812
1.817
1.821
1.824
1.827
1.830
1.835
1.840
1.894
75
1.817
1.821
1.825
1.829
1.832
1.835
1.840
1.844
1.899
80
1.826
1.830
1.833
1.836
1.839
1.844
1.849
1.903
85
1.833
1.837
1.840
1.843
1.848
1.852
1.907
90
1.840
1.844
1.846
1.852
1.856
1.911
95
1.847
1.850
1.855
1.859
1.914
100
1.853
1.858
1.862
1.917
110
1.863
1.867
1.992
120
1.871
1.926
Table 17-1 Radial Contact Ratio of Standard Spur Gears, ea (a = 20°)
