Hitachi DH 40MR Technical And Service Manual page 18

Slip clutch mechanism
The slip clutch mechanism is described below with reference to Fig. 7. The bevel pinion and the gear holder
are coupled together by the key and press-fitting. Spring (C) and needle pins are housed in elongated
grooves of the gear holder. The needle pin is pressed against the inner face of second gear by spring (C) to
allow idle rotation of the second gear relative to the gear holder. When an excess torque is exerted on the
bevel pinion shaft, the needle pin is raised upon the projection of the second gear against the load of spring
(C) to allow idle rotation of the second gear. With the arrangement, the clutch slips when an excessive torque
is applied to the working tool as when the drill bit contacts steel bar/wire in the concrete, protecting the
operator from unexpected motion of the side handle.
Bevel pinion
Gear holder
Tool holder
Tool
Needle roller (2 pieces)
Forward Backward
Front cap
Second gear
Gear holder groove
Fig. 7
Grip
Grip
Key rail (3 pieces)
Fig. 8
--- 15 ---
Gear holder
Bevel pinion
Cross section A - A
The tool inlet is covered with the front cap
(made of rubber) to prevent chips from
entering inside. Two needle rollers fall into
the round groove of the drill bit to retain the
working tool, and three key rails transmit the
rotation torque. To attach a working tool, align
the groove positions turning the working tool,
then insert the working tool into the hole until
it contacts the innermost end of the hole.
Releasing the grip reverts the grip and
secures the tool in place. To remove the tool,
fully pull the grip backward and pull out the
tool (Fig. 8).
Needle pin
Spring (C)
Key