The Hertz contact stress and transmission error of the helical gear products of an enterprise before and after the experience of modification are shown in the table.
| Programme | Shaping method | Modification quantity（μm） | Transmission error（μm) | Hertz contact stress (N/mm2) |
| 1 | Unmodified | 0 | 2.351 | 394.264 |
| 2 | Tooth profile drum+tooth direction drum | 25+25 | 12.910 | 1153.505 |
The transmission error and Hertz contact stress of helical gear pair have not decreased, but have increased significantly, from 2.351 before the modification μ M, 394.264 N/mm2 rise to 12.910 μ M, 1153.505 N/mm2, with the rise of up to 549.1% and 292.6% respectively, so that the trajectory of the helical gear will be seriously deviated during meshing, resulting in strong impact between the teeth, causing abnormal vibration of the helical gear pair, and the strength of the teeth will be greatly reduced, which will ultimately affect the service life of the helical gear.