Some interesting characteristics of trochoids are discussed in this paper a
nd a new concept of virtual involute is introduced. These characteristics p
rove very useful in determining the exact tooth fillet shape generated by r
acks consisting of circular arcs and straight line segments. The fillet cur
ves generated by racks with a protuberance or with a chamfered tip are disc
ussed in detail. A numerical example is given to illustrate their applicati
on. (C) 1999 Elsevier Science Ltd. All rights reserved.