Page 374 - Gear Technology Solutions

The addition of the two outer calculation loops (visualized in Figure 14) with
the strategy of increasing one of the front clean up depths (either on the inside
blade or on the outside blade) resulted in a 3-face blade spacing, which dupli-
cated precisely the original 2-face reference blade. Calculations with the post-
revision TREFACE program in connection with an input value for the effective
cutting edge hook angle between 0° and +1° deliver a new generation 3-face
blades, which eliminate all length crowning errors and reduce about 85% of the
flank twist experienced with the pre-revision software.

Practical proof of this is shown in the flank deviation graphic in Figure 21. The
3-face blade calculation was repeated with the post-revision TREFACE pro-
gram. As input for the effective hook angle values of inside and outside blades,
the recommendation above was applied. Pinions manufactured with the new 3-
face blade geometry in a cutter head with 12° slot inclination angle are meas-
ured with the standard CAGE download file (based on 2-face blades with 12°
blade side rake angle used in a cutter with 4.42° slot inclination) result in a sin-
gle micron flank form deviation, with an excellent Sum of Errors Squared of
0.000 000 46inch².

26.8 Summary

In face hobbing the cutting-edge hook angle as well as the spacing between
outside and inside blades has an influence on the flank geometry of the manu-
factured bevel gears. In an industrial environment, the basic blade geometry
(reference blade) is defined with the original job design early on but the deci-
sion “2-face or 3-face blades” is made only much later in the process. Manu-
facturers like not to accept that their decision to use 3-face ground blades
could change the flank geometry development of their already approved de-
signs. This was the reason for a major revision of the Gleason blade summary
calculation program TREFACE.

3-face blades ground with summaries calculated with the post-revision
TREFACE software do not create length crowning differences compared to the
2-face reference blade. All flank twist or bias differences between gears cut
with 3-face blades versus the 2-face reference blade can be eliminated or
greatly reduced, if the effective cutting edge hook angle is chosen between 0°
and 1°. The new calculation allows the user to make the decision to use cut-
ters with slot inclinations higher than the reference cutter in connection with 3-
face ground blades much later than the development of the gearset design.
This enables a manufacturer to develop and manufacture in different locations
without the potential of discrepancies between desired and achieved flank ge-
ometry. It also makes the manufacture of the same gearset design possible in
different locations without noticeable differences.

359