Page 335 - Gear Technology Solutions

23.3 Top Slope and Stepping of Cutter Blades for Formate Face
Hobbed Members

Ring gears in face hobbing generally do not have length crowning tilt. The
reason becomes evident when observing Figure 2. The cutter head is tilted
towards the generating plane which can cause the blades to mutilate the
toothed section at the opposite side of the blank due to the flat design of most
ring gears. Because this is not a concern in pinion cutting, the entire length
crowning tilt is commonly applied to the pinion.

In cutting of Formate ring gears, the cutter head has to be positioned above
center which achieves the same effect as a cutter head tilt shown in Figure 2.
If in certain cases some small amount of length crowning tilt is applied to a
Formate ring gear then a cutting above center as shown in Figure 4 is
required.

Figure 4: Top slope for Formate ring gears

Stepping of the blade in a Formate process is not required because of the
missing generating motion which changes the blade inclination relative to the
slot symmetry line. In spite of this, a top slope angle on the inside and outside
blade top (l IB and l OB) is desired and can be calculated using the simplified
formulae in Figure 4, assuming that the difference between blade angles and
corresponding tooth pressure angles are similar to the length crowning tilt

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