Page 120 - Gear Technology Solutions

All input parameters of the flank form generation have been set to receive an
uncorrected gearset, without length and profile crowning. In the case of correct
kinematic coupling conditions, the expected result would reflect a perfectly
conjugate gearset. Conjugate means that along the contact lines and along the
path of contact no deviations in the Ease-Off graphic are visible. The present
Ease-Off, left in Figure 6 is warped and shows a large profile crowning. The
Tooth contact to the right in Figure 6 looks bizarre due to the negative length
crowning and the motion transmission errors are peaks without crossing points
(transfer points) between them.

The input parameter for length crowning will introduce a dish angle to offset
the negative length crowning and add the desired length crowning. Also, the
input parameter for the profile crowning, Dg M can, within limits, reduce to profile
crowning in order to achieve a desirable amount. However, the generating
flats, when extended towards the crossing point between pinion and gear axis,
will not intersect with the crossing point and certain mesh disturbances will
occur. Motion errors of conventionally cut straight bevel gears are between
300 and 1000 microradians, based on the non-conjugate generating process.

The limitations or restrictions of the conventional straight bevel gears base on
the limitations of the mechanical bevel gear generators, where the pressure
angle and the cutter dish angle are connected by the fixed tilt angle of the
interlocking cutters. For example, a fixed cutter tilt of 24° allows 4° of dish
angle when the blade pressure angle is 20°. A deviation from the theoretical
ratio of roll is often used to realize larger or smaller dish angles by maintaining
the correct pressure angle. Changing the ratio of roll often causes undercut or
reduces the active working depth.

Figure 6: Contact analysis when generating on root cone

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