Tool Structure - Hitachi DH 24PD3 Technical Data And Service Manual

8-3. Tool Structure

While the structure is essentially the same as the Model DH 24PD2, the descriptions below are included to
enhance your understanding of the tool and its mechanisms.
Transmission of rotation
Unlike conventional rotary hammers, the armature shaft in the Model DH 24PD3 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 24PD3 more compact for easier handling and operability. Thus, the appearance of the Model
DH 24PD3 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 pinion assembled on the second shaft via the first gear,
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 falling.
Piston reciprocating mechanism
In conventional rotary hammers, 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 24PD3, 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, rotation of the armature and dust shaft
(coupled by a spline) 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 a piston pin, and causes the reciprocating motion of the
piston.
Armature
Motor shaft
Piston pin
First gear
Reciprocating Ring groove
bearing
Fig. 5
--- 15 ---
Second gear
Piston
Cylinder
Second shaft
Clutch
Steel ball
Tool shaft
Key rail (2 pcs.)