Hitachi DH 24PF3 Technical Data And Service Manual page 20

Slip mechanism
The slip mechanism in the Model DH 24PF3 consists of a coil spring which applies a pre-set amount of
pressure to ensure the interlocking of three claws provided on the flange of the cylinder (the final rotating
shaft) and six matching claws provided on the face of the second gear, by which rotation is transmitted to the
cylinder. The second gear is fitted to the cylinder with a certain amount of play.
If an excessively large torque is applied to the tool shaft (cylinder), the force of the torque will exceed the
pressure of the coil spring and cause the claws on the second gear to disengage from and ride over the claws
on the cylinder so that the second gear idles and does not transmit rotation. Even if the drill bit comes in
contact with a reinforcing bar within the concrete, causing sudden excessive torque, the slip mechanism
functions to prevent damage to the gears, and possible loss of control of the tool by the operator.
Sealed and dustproof construction
The gear cover is totally enclosed by oil seals, O-rings and other devices to prevent leakage of lubricating
grease, and to keep dust and dirt out of the internal mechanisms. The drill bit chuck portion is protected by a
rubber front cap to keep out dust and chips which could cause improper fitting of the drill bit and/or other faulty
operation of the chuck portion. The speed control switch is also a fully dust-proofed type to prevent dust and
chips from entering the handle section and causing possible operational trouble or a break down of the
insulation.
Speed control
The Model DH 24PF3 is equipped with a variable speed control switch which permits free change of the
rotation speed and hammering force. When drilling in fragile materials, pull the switch trigger gently for low
rotation speed (hammering force) to achieve optimum results.
Note that the switch trigger cannot be pulled to the full but up to the half in the reverse drilling, and the speed
is about half of the forward drilling. In addition, the switch stopper cannot be used in the reverse drilling.
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