PURPOSE: To reduce an amount of abrasion loss in a work wheel as well as to improve its service life so sharply by setting the material of this work wheel for an orthogonal shaft speed reduction gear to brass added wided with silicon and manganese, using specified mineral oil for lubricating grease as additives, and applying an ureal thickening agent for the end.

CONSTITUTION: Material for a worm wheel 2 is brass added with silicon and manganese, separating particles out of an intermetallic compound of silicon- manganese being very high in hardness in structure, and it is resistible to frictional contact in its partial structure owing to this intermetallic compound. Despite this fact, its surface hardness is average of other copper alloys as in HV180, having slidability and conformability. Lubricating grease 3 is composed of a ureal thickening agent in addition to mineral oil, and as to additives, dialkyldithiol carbamic acid molybdeum (MoDTC) and dialkyldithionic acid molybdenum (MoDTP) are added, whereby molybdenum disulfide is formed on a lubricating surface, through which wear resistance is improved. In this connection, grease consistency should be set to a range of 380 to 410.