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        (m_p)_trans = value per equation 18
        (m_p)_axial =   F  = F tan y   =  F sin y   
                           P_a        P_c               P_cn
and F = face width of gear.

5.8.5 Involute interference — Helical gears cut with standard normal pressure angles can have  considerably higher pressure angles in the plane of rotation (see equation 29), depending on the helix angle. Therefore, referring to equation 19, the minimum number of teeth without undercutting can be significantly reduced and helical gears having very low tooth numbers without undercutting are feasible.

5.9  Crossed Helical Gear Meshes

These are also known as spiral and screw gears. They are used for interconnecting skew shafts, such as in Figure 1.29. They can be designed to connect shafts at any angle, but in most applications the shafts are at right angles.
          5.9.1   Helix angle and hands — The helix angles need not be the same. However, their sum must  equal the shaft angle:
                    y₁ + y₂ = q                                                                                             (33)

where:

y₁, y₂ = the respective helix angles of the two gears
q          = shaft angle (the acute angle between the two shafts when viewed in a direction parallel
               ing a common perpendicular between the shafts)

Except for very small shaft angles, the helix hands are the same.

5.9.2 Pitch — Because of the possibility of ditferent helix angles for the gear pair, the transverse  pitches may not be the same. However, the normal pitches must always be identical.

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