To surely and inexpensively form a pair of acute-angled cracking grooves on the inner peripheral surface of a large-ended hole of an integrally molded connecting rod to improve breakableness of the connecting rod.
A driving pulley 62 rotates with a rotary driving source 58 provided on a body 16 driven, rotary driving force of the pulley 62 is transmitted via a driving force transmission belt 68 to a driven pulley 64, and a groove machining part 26 integrally coupled with the pulley 64 is rotated. By inserting the groove machining part 26 into the large-ended hole 22 of the connecting rod 20, a first groove with an approximately V-shaped cross section is formed by a cutter member 40 of the machining part 26, and in addition a second groove with an approximately V-shaped cross section having a symmetric shape of the first groove is formed at a position opposite to the first groove with respect to the axial line of the connecting rod 20.
OTA SHIGEO
Toshiyuki Miyadera
Tatsuhiko Sato
Next Patent: WORKING DEVICE FOR CRACKING GROOVE FOR CONNECTING ROD