Reference Material; Lubrication; Tool Structure - Hitachi DH 24DV Technical Data And Service Manual

8. REFERENCE MATERIAL

8-1. Lubrication

It is not necessary to replenish the grease lubricant unless the tool is disassembled or there is grease leakage
due to a defective seal. Special grease is used in the striking section. Should the striking section (within the gear
cover) be disassembled, carefully remove the old grease from all parts and, on reassembly, insert 50 g (1.8 oz) of
new grease into the gear cover and 10 g (0.4 oz) into the groove of the inner cover. Be careful not to exceed the
designed amount of grease. Excessive grease will reduce striking efficiency.
Apply Molub Alloy No. 777-1 grease to the outer circumference of the clutch groove and the pin portion of the
change lever.

8-2. Tool Structure

While the structure is essentially the same as that of the Model DH 24PB2, the description below are included to
enhance your understanding of the tool and its mechanisms.
Transmission of rotation
Unlike conventional hammer drills, the armature shaft in the Model DH 24DV is in parallel with the tool shaft -
the same structure that is employed in most impact drills. This structure was adopted in order to make the
Model DH 24DV more compact for easier handling and operability. Thus, the appearance of the Model
DH 24DV is similar to that of an impact drill. The rotation of the armature is transmitted to the second shaft via
the first gear, and causes it to rotate. The second shaft engages the second gear mounted on the outer
circumference of the cylinder. The cylinder is coupled to the second gear by means of a slip mechanism, and
they rotate together. The end of the cylinder also functions as the drill bit retainer. The cylinder is key-
connected to the inserted drill bit by means of two key rails, and transmits rotation to the drill bit. A steel ball is
used to prevent the bit from coming off.
Piston reciprocating mechanism
In conventional hammer drills, a piston is caused to reciprocate by a connecting rod and crank shaft, and the
crank shaft and the cylinder axis are at right angle to each other. Accordingly, the armature shaft and the
cylinder axis are at a right angle to each other. In the Model DH 24DV, through adoption of a spiral drive
system (a mechanism using a reciprocating bearing), a more compact design has been achieved by arranging
the armature shaft in parallel with the cylinder axis. Referring to Fig. 5, the rotation of the armature is
transmitted to the second shaft via the first gear. The second shaft rotation is further transmitted through a
spline to the clutch, which engages with a reciprocating bearing and causes it to rotate. However, as
illustrated, circular grooves on the inner race of the reciprocating bearing are positioned on an angle of
inclination with relation to the second shaft. The rotation of the inner race and the shaft causes that angle of
inclination to change regularly forward and back with relation to the second shaft, and produces a rocking
motion to the outer race of the reciprocating bearing. Finally, a rod extending from the outer race of the
reciprocating bearing is connected to the piston by the piston pin, and causes the reciprocating motion of the
piston.
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