Hitachi DH 25PA Manual

POWER TOOLS
TECHNICAL DATA
AND
SERVICE MANUAL
HAMMER DRILL
DH 25PA, DH 25PB
SPECIFICATIONS AND PARTS ARE SUBJECT TO CHANGE FOR IMPROVEMENT
LIST Nos. DH 25PA: E453
DH 25PB: E454 Nov. 1999
D
MODELS
DH 25PA
DH 25PB

REMARK:
Throughout this TECHNICAL DATA AND SERVICE MANUAL, a symbol(s)
is(are) used in the place of company name(s) and model name(s) of our
competitor(s). The symbol(s) utilized here is(are) as follows:
Symbols Utilized Competitors
Company Name Model Name
MAKITA HR2010
C

Page
CONTENTS
[ Business Section ]
1. PRODUCT NAME
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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2. MARKETING OBJECTIVE
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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3. APPLICATIONS
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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4. SELLING POINTS
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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4-1. Selling Point Descriptions
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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5. SPECIFICATIONS
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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5-1. Specifications
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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5-2. Optional Accessories
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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6. COMPARISONS WITH SIMILAR PRODUCTS
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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6-1. Specification Comparisons ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 11
6-2. Drilling Speed Comparisons •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 12
7. PRECAUTIONS IN SALES PROMOTION•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 13
7-1. Handling Instructions
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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7-2. Caution Plate
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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8. REFERENCES
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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8-1. Grease Replacement Procedures
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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8-2. O-Ring Replacement
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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8-3. Structure of the DH 25PAand DH 25PB Hammer Drills •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15
8-4. "Rotation Only" and "Rotation + Striking" Changeover Mechanism (DH 25PB only) •••••••••••••••••••• 17
8-5. "Rotation Only" (no striking) (DH 25PB only) •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 17
8-6. Drill Bits
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••18
8-7. Chuck Section
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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8-8. Dust Collector (B)
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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[ Service Section ]
9. PRECAUTIONS IN DISASSEMBLYAND REASSEMBLY
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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9-1. Disassembly •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 21
9-2. Reassembly •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 24
9-3. Tightening Torque •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 25
9-4. Wiring Diagrams •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 26
9-5. Wiring Work ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 27
9-6. Insulation Tests •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 28
9-7. No-Load Current Value ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 28
10. STANDARD REPAIR TIME (UNIT) SCHEDULES ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 29
[ Appendix ]
Assembly Diagram for DH 25PA•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 30
Assembly Diagram for DH 25PB •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 36
Notice for use
Specifications and parts are subject to change for improvement.
Refer to Hitachi Power Tool Technical News for further information.

--- 1 ---
1. PRODUCT NAME
Hitachi Hammer Drill (Rotation + Striking: single-mode), Model DH 25PA
Hitachi Hammer Drill (Rotation + Striking, Rotation only: dual-mode), Model DH 25PB
2. MARKETING OBJECTIVE
The Model DH 25PB is a major modification of the Model DH 20V. With a more powerful motor and striker, this
hammer drill provides improved concrete drilling capacity (maximum drill bit dia. 25 mm) and faster drilling speed
than the previous model.
The Model DH 25PB is compact and lightweight, and the double-layer molded handle consists of a plastic resin
base covered with a soft plastic layer to ensure a soft touch and firm, non-slip grip. This series includes the
single-mode operation hammer drill Model DH 25PA equipped with a "Rotation + Striking" function, which is based
on the Model DH 25PB.
3. APPLICATIONS
(1) Rotation and striking function
Drilling anchor holes
Drilling holes in concrete, tile, brick and similar materials
(2) Rotation only function
Drilling holes in steel and wood (with chuck adapter)
Tightening and loosening machine screws and wood screws (with chuck adapter)
[Typical applications]
Air conditioning ••••••••••••••••••••••••••••••••Installation of air conditioners, water coolers and heaters, and air ducts
Piping and plumbing •••••••••••••••••••••••• Installation of gas, water, and sanitary facilities
Electrical work •••••••••••••••••••••••••••••••••Installation of light fixtures and various electric appliances
Interior decoration ••••••••••••••••••••••••••• Installation of seating, display stands, and partitions
Other civil engineering, construction and repair work

--- 2 ---
4. SELLING POINTS
Compact and lightweight: Overall length 318 mm (12-17/32"), Weight DH 25PA 3.3 kg (7.3 lbs.)
DH 25PB 3.4 kg (7.5 lbs.)
DH 25V: Overall length 352 mm (13-7/8"), Weight 4.4 kg (9.7 lbs.)
DH 20V: Overall length 352 mm (13-7/8"), Weight 3.1 kg (6.8 lbs.)
B : Overall length 287 mm (11-5/16"), Weight 3.1 kg (6.8 lbs.)
Variable speed control switch
Fast drilling speed: About 20% faster than the Model DH 20V when the pressing force is 10 kgf.
Powerful 650 W motor
(DH 25V: 600 W)
(DH 20V: 460 W)
Soft-touch handle
Rotation + Striking, Rotation only: dual-mode (DH 25PB only)
Rotation + Striking : single-mode (DH 25PA)
NOTE: The Model DH 25PA does not have a changeover knob.

--- 3 ---
4-1. Selling Point Descriptions
4-1-1. Fast drilling speed
The drilling speed is 20% faster than the Model DH 20V as the Models DH 25PA and DH 25PB have great striking
energy owing to the optimum design of the rotation speed, striking frequency and the weight of striker. The
Models DH 25PAand DH 25PB can drill holes in concrete with a maximum drill bit diameter of 25 mm.
4-1-2. Powerful 650 W motor
Although the motor is the same size as the Model DH 20V, power consumption was raised to 650 W by improving
the winding specifications and the motor cooling efficiency. These are powerful hammer drills that are also
compact and lightweight.
4-1-3. Variable-speed control switch
The variable-speed control switch allows the rotation speed to be changed freely throughout the drilling operation.
This permits easy centering and positioning, and ensures more effective drilling of fragile materials such as tile
and brick.
4-1-4. Soft-touch handle
The double-layer molded handle consists of a plastic resin base covered with a soft plastic layer to ensure a soft
touch and firm, non-slip grip of the handle.

--- 4 ---
5. SPECIFICATIONS
5-1. Specifications
Model DH 25PA DH 25PB
Capacity Concrete
Steel
Wood
Power source
Voltage, current and
power input
Rotation
speed No-load
Full-load
Full-load blow rate
Type of motor
Type of switch
Type of handle
Enclosure
Function mode(s)
Weight
Packaging
Standard accessories
Net*
Gross
3.4 --- 25 mm (1/8" --- 1")
13 mm (1/2")
32 mm (1-1/4")
AC single phase 50 Hz or 60 Hz
0 --- 1100 /min
0 --- 800 /min
0 --- 4000/min
AC single-phase commutator motor
Variable switch
D-type handle and side handle
Materials:
Gear cover
Crank case ••••••••Aluminum alloy die casting (silver)
Cylinder case
Housing (green)
Handle cover (gray)
Handle ••••••••Glassfiber reinforced
Tail cover polyamide resin (black)
Grip
Rotation and striking
3.4 kg (7.5 lbs.)3.3 kg (7.3 lbs.)
5.9 kg (13.0 lbs.) 6.0 kg (13.2 lbs.)
Rotation and striking
Rotation only
Corrugated cardboard box with case
(1) Case ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
(2) Side handle •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
(3) Stopper •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
(4) Dust cup •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
Voltage (V)
Current (A)
Power input (W)
110 115 120 127 220 230 240
6.2 5.9 5.7 5.4 3.1 3.0 2.8
650
*: Weight excludes cord and side handle.

--- 5 ---
5-2. Optional Accessories
A. Drilling anchor holes (rotation + striking)
Drill bit (slender shaft)
(1) Drill bit (slender shaft) (2) Adapter for slender shaft
(SDS-plus shank)
+
Drill bit (taper shank)
+
(1) Drill bit (taper shank) (2) Taper shank adapter
(SDS-plus shank) (3) Cotter
13 mm Hammer drill chuck (DH 25PB only)
For drilling operations when using a straight shank bit for impact drilling with a hammer drill
+
Drill bit (slender shaft)
Outer dia. (mm)
3.4 (1/8")
3.5 (9/64")
Effective length (mm)
45 (1-25/32")
45 (1-25/32")
Overall length (mm)
90 (3-17/32")
90 (3-17/32")
Code No.
306369
306368
Code No.
306370
Adapter for slender shaft
(1) Drill bit (taper shank)
Outer dia. (mm)
11 (7/16")
12.3 (31/64")
12.7 (1/2")
14.3 (9/16")
14.5 (73/128")
17.5 (11/16")
Code No.
944460
944461
993038
944462
944500
944463
Type
Morse taper
No. 1
Code No.
303617
Code No.
944477
(3) Cotter(2) Taper shank adapter
21.5 (27/32") 944464 Morse taper
No. 2 303618
Straight shank bit for
impact drills 13mm (1/2") Hammer drill
chuck (SDS-plus shank) Chuck wrench
Rubber cap
Part name
13mm (1/2") Hammer drill chuck
(including chuck wrench)
Chuck wrench
Rubber cap
Code No.
303332
303334
303335
Part name Code No.
A-taper
B-taper 303619 303620 Taper shank adapter (A-taper or B-taper) is provided as an
optional accessory, but drill bit is not provided.

--- 6 ---
B. Anchor setting
Anchor setting bar to permit anchor setting operation with the hammer drill
Anchor setting bar
Anchor setting adapter (SDS-plus shank)
Part name
W - 1/4 Anchor setting adapter -A
W - 5/16 Anchor setting adapter - A
W - 3/8 Anchor setting adapter -A
W - 3/8 Anchor setting adapter -A
Internal cone type
Overall length Code No. Part name Overall length Code No.
260
260
160
260
302976
302975
303621
302974
W - 1/4 Anchor setting adapter - B
W - 5/16 Anchor setting adapter - B
W - 3/8 Anchor setting adapter - B
W - 3/8 Anchor setting adapter - B
260
260
160
260
302979
302978
303622
302977
External cone type
Anchor setting bar for manual anchor setting
Anchor setting adapter
Part name
W - 1/4 Anchor setting adapter -A
W - 5/16 Anchor setting adapter - A
W - 3/8 Anchor setting adapter -A
W - 1/2 Anchor setting adapter -A
W - 5/8 Anchor setting adapter -A
Internal cone type
Code No. Part name Code No.
971794
971795
971796
971797
971798
971799
971800
971801
971802
971803
External cone type
+
Manual hammer
W - 1/4 Anchor setting adapter - B
W - 5/16 Anchor setting adapter - B
W - 3/8 Anchor setting adapter - B
W - 1/2 Anchor setting adapter - B
W - 5/8 Anchor setting adapter - B
C. Large hole boring (rotation + striking)
Center pin, core bit, core bit shank and guide plate
(Guide plate)
+++
Center pin Core bit Core bit shank
(SDS-plus shank)
(1) Center pin (Do not use bit with outer diameter of 25 mm (31/32") and 29 mm (1-5/32").
Center pin (A)
Center pin (B)
Core bit (outer diameter) 32, 35, 38 mm (1-1/4", 1-3/8", 1-1/2")
Core bit (outer diameter) 45, 50, 65, 80, 90 mm (1-25/32", 2", 2-9/16", 3-5/32", 3-9/16")
Code No. 982684
Code No. 982685

--- 7 ---
Core bit (outer diameter) (mm) Code No. Core bit (outer diameter) Code No.
(2) Guide plate
32 (1-1/4") 982686 50 (2") 982690
35 (1-3/8") 982687 65 982691
38 (1-1/2") 982688 80 982692
45 (1-25/32") 982689 90 982693
Outer diameter (mm) Code No. Outer diameter (mm) Code No.
(3) Core bit with guide plate (the guide plate is not required for 25 mm (31/32") and 29 mm (1-5/32") outer
diameter core bits.)
25 (31/32") 982672 45 (1-25/32") 982677
29 (1-5/32") 982673 50 (2") 982678
32 (1-1/4") 982674 65 982679
35 (1-3/8") 982675 80 982680
38 (1-1/2") 982676 90 982681
(4) Core bit shank (SDS-plus shank)
Core bit shank (A)
Core bit shank (B)
Core bit (outer diameter) 25 --- 38 mm
(31/32"
--- 1-1/2")
Overall length 105 mm (4-1/8")
Overall length 300 mm (11-52/64")
Core bit (outer diameter) 45 --- 90 mm
(1-25/32"
--- 3-9/16")
Overall length 300 mm (11-52/64")
Code No. 303625
Code No. 303626
Code No. 303627
D. Bolt placing operations with chemical anchor (rotation + striking)
(Standard sockets available on the market)
+
12.7 mm (1/2") Chemical anchor adapter (SDS-plus shank)
19 mm (3/4") Chemical anchor adapter (SDS-plus shank)
12.7 mm (1/2") Chemical anchor adapter
19 mm (3/4") Chemical anchor adapter
Part name Code No.
303044
303045
E. Demolishing operations (rotation + striking)
Bull point (round type only)
(SDS-plus shank)
Code No. 303046

--- 8 ---
F. Drilling hole (rotation only) ... for drilling holes in steel and wood (DH 25PB only)
Drill chuck
(13VLA)
+
Chuck adapter (D)
(SDS-plus shank)
Chuck adapter (D) (for SDS-plus shank type)
13 mm (1/2") Drill chuck 13VLA (with chuck wrench)
Part name Code No.
303624
950272
Chuck wrench

--- 9 ---
Drill chuck
(13VLA)
+
Chuck adapter (D)
(SDS-plus shank)
Chuck wrench
G. Driving screws (rotation only) (DH 25PB only)
(1) Cross-recessed head (Phillips) bit
[Overall length: 70 mm]
(For use with cross-recessed head (Phillips) screw)
(2) Slotted-head (minus) bit
[Overall length: 50 mm]
(For use with slotted-head (minus) screw)
Stamped bit No. Tip thickness
Bit No.
No. 2
No. 3
Code No.
955654
955655
Applicable screw dia. (mm)
3 --- 5
6 --- 8
Bit tip
thickness
0.8
1
Code No.
955658
955673
Applicable screw dia. (mm)
4
5 --- 6
H. Drilling screws (rotation only) (DH 25PB only)
Plus (Phillips) driver bit [overall length: 25 mm] (for cross-recessed head (Phillips) screws)
Bit No.
+
Chuck adapter (D)
(SDS-plus shank)
Bit No.
No. 2
No. 3
Screw size
3 --- 5 mm
6 --- 8 mm
Code No.
971511Z
971512Z

--- 10 ---
I. Grease for electric impact drill
Containing 500 g (17.64 oz): Code No. 980927
Containing 30 g (1.06 oz): Code No. 981840
70 g (2.5 oz): Code No. 308471
J. Dust cup, dust collector (B)
Dust collector (B) ass'y
Code No. 306885

--- 11 ---
6. COMPARISONS WITH SIMILAR PRODUCTS
6-1. Specification Comparisons
Maker
Model
Capacity
Concrete
Steel
Wood
mm
mm
mm
W
/min.
/min.
/min.
dB(A)
Power input
No-load rotation speed
Full-load rotation speed
Full-load blow
No-load sound
pressure level
Change mode
Variable speed control
(Note 1)
Safety-release clutch
(Note 1)
Bit drive system
Dimensions
Weight (Note 2)
Length
Height
Width
mm
mm
mm
kg
Hitachi
DH 25PA DH 25PB DH 20V DH 25V C
25 (1")
13 (1/2")
32 (1-1/4")
25 (1")
13 (1/2")
32 (1-1/4")
20 (25/32")
13 (1/2")
15 (19/32")
25 (1")
13 (1/2")
20 (25/32")
13 (1/2")
24 (15/16")
650 650 460 520 600
0 --- 1,100 0 --- 1,100 0 --- 900 0 --- 800 0 --- 900
0 --- 800 0 --- 800 0 --- 700 0 --- 650 0 --- 735
0 --- 4,000 0 --- 4,000 0 --- 3,500 0 --- 3,150 0 --- 4,000
89 89 92 85 82
1 mode 2 modes 2 modes 2 modes 1 mode
SDS-plus shank SDS-plus shank SDS-plus shank
Round shank SDS-plus shank Round shank SDS-plus shank Round shank
318 (12-1/2") 318 (12-1/2") 320 (12-19/32") 352 (13-7/8") 287 (11-9/32")
200 (7-7/8") 210 (8-1/4") 200 (7-7/8") 221 (8-43/64") 214 (8-15/32")
92 (3-5/8") 92 (3-5/8") 94 (3-43/64") 100 (4") 91 (3-19/32")
3.3 (7.3 Ibs.) 3.4 (7.5 Ibs.) 3.1 (6.8 Ibs.) 4.4 (9.7 Ibs.) 3.1 (6.8 Ibs.)
Note 1) Mark " " •••Equipped, Mark " " •••Not equipped.
2) Weight excludes cord and side handle.
------

--- 12 ---
6-2. Drilling Speed Comparisons
Drilling speed depends on the operating conditions. The test results shown in Fig. 1 are based on actual tests at
the factory and should be used as a reference only.
The drill bits which used in the test are the Hitachi genuine SDS-plus shank bits.
06 8 10 12 14
Drill bit dia. (mm)
Drilling speed (mm/min.)
16 18 20 22 25
100
200
300
400
500
600
700
C
DH 25PA
DH 25PB
DH 25V
DH 20V
Pressing force: 98 N (10 kgf)
Test material: Concrete panel with
a compression strength of
2352 N/cm
2
(240 kgf/cm
2
)
Fig. 1 Drilling speed comparisons (downward drilling)

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CAUTION
Read thoroughly HANDLING INSTRUCTIONS before use.
7. PRECAUTIONS IN SALES PROMOTION
In the interest of promoting the safest and most efficient use of the Models DH 25PA/PB Hammer Drills by all of
our customers, it is very important that at the time of sales the salesperson carefully ensures that the buyer
seriously recognizes the importance of the contents of the Handling Instructions, and fully understands the
meaning of the precautions listed on the Caution Plate attached to each tool.
7-1. Handling Instructions
Although every effort is made in each step of design, manufacture and inspection to provide protection against
safety hazards, the dangers inherent in the use of any electric power tool cannot be completely eliminated.
Accordingly, general precautions and suggestions for the use of electric power tools, and specific precautions and
suggestions for the use of the Hammer Drill are listed in the Handling Instructions to enhance the safe, efficient
use of the tool by the customer. Salespersons must be thoroughly familiar with the contents of the Handling
Instructions to be able to offer appropriate guidance to the customer during sales promotion.
7-2. Caution Plate
The following basic safety precautions are listed on the Name Plate attached to the main body of each tool.
However, these precautions are not listed for European countries.
For Asia and Oceania
WARNING
To reduce the risk of injury, user must read and
understand instruction manual.
AVERTISSEMENT
Afin de rèduire le risque de blessures, l'utilisateur doit lire
et bien comprendre le mode d'emloi.
For the U.S.A and Canada

--- 14 ---
8. REFERENCES
8-1. Grease Replacement Procedures
The electro-pneumatic hammering section and gear change section each use a different kind of grease. It is not
necessary to replenish the grease unless the tool is disassembled for repair or there is grease leakage due to a
damaged seal.
A special grease is used for the hammering section. To change the grease in the hammering section (Cylinder
Case and Crank Case), carefully wipe the old grease off the parts, and supply 20 g in the Cylinder Case and
17.5 g in the Crank Case (on the Connecting Rod side). Take care not to overfill the grease as an excessive
amount of grease can cause hammering failure.
The gear change section (in the Gear Cover) uses Hitachi Motor Grease No. 29 for power tools. Supply with 60 g
of this grease. Do not use the special grease used for the hammering section, or it will leak into the motor parts
and result in a failure of the tool.
8-2. O-Ring Replacement
The O-ring (attached to the Striker and Piston) plays an important role to ensure air tightness. Despite its
prolonged service life due to a special rubber material, it will inevitably wear out. Early replacement, preferably
once every six months, is recommended.

--- 15 ---
Front cap
8-3. Structure of the DH 25PA and DH 25PB Hammer Drills
Grip Needle pinCylinder
Steel ball
Second
hammer Striker
Air chamber
Third
gear Piston Connecting
rod
Crank shaft
First gear
Key rail
(2 pieces)
Retainer
sleeve
O-ring
Second gear
Third pinion
Armature
Handle
Fig. 2
Transmission of rotation
Transmission of rotation is described with reference to Fig. 2. The gear arrangement of the Models DH 25PA
and DH 25PB is the same as that of Model DH 20V.
Rotation of the armature is transmitted to the second gear to rotate the third gear via the slip mechanism
between the second gear and the third pinion shaft. Rotation of the third gear is then transmitted to the
cylinder threaded onto the third gear. Rotation of the cylinder is transmitted to the retainer sleeve coupled
together by means of three needle pins, and then to the drill bit inserted into the retainer sleeve by way of two
key rails and a steel ball which hold the bit.
Striking function
Rotation of the armature is transmitted to the crank shaft and the connecting rod, and the piston reciprocates
within the cylinder. As the piston reciprocates, the changing air pressure inside the air chamber between the
piston and the striker causes the striker to move and continuously strike against the end of the second
hammer. At the same time, the changing air pressure within the air chamber which moves the striker also
provides an "air cushion" which absorbs the impact of the striking action.

--- 16 ---
Idle striking prevention mechanism
The idle striking prevention mechanism in the Models DH 25PA and DH 25PB is different from that of
conventional hammer drills. When the drill bit is lifted from the concrete surface on completion of drilling, the
second hammer moves to the position indicated by the continuous lines in Fig. 3, and the protruding portion at
the tip of the striker is gripped by the O-ring mounted on the inner wall of the retainer sleeve. Accordingly, the
air-escape slot is opened and there is no change in the air pressure within the air chamber. That prevents
movement of the striker (idle striking operation). The gripping force of the O-ring on the striker is so small in
comparison with the conventional mouth system that practically no pressing force at all is required to restart
the striking operation.
Cylinder
Travel
distance Striker Air-escape slot
O-ring
Second hammer
Retainer sleeve
Tool shaft
Fig. 3
Slip mechanism
A clutch plate holding a steel ball is inserted between the second gear and the spring plate as a slip
mechanism in the Models DH 25PA and DH 25PB. If an excessively large torque is applied to the tool shaft,
the second gear idles and does not transmit rotation.
The slip torque is adjusted by the slip plate and the belleville (coned disk) spring pressure. Even if the drill bit
comes in contact with a reinforcing bar within 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. The slip
torque is set at 2.1 to 3.1 kg•m on the tool shaft.

--- 17 ---
Sealed and dust-proof construction
The cylinder case 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 cap (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 switch is also fully
dust-proofed to prevent dust and chips from entering the handle section and causing possible operational
trouble or a breakdown of the insulation.
Speed control
The Models DH 25PA and DH 25PB are equipped with a variable speed control switch which permits free
Adjustment of the rotation speed and striking force. When drilling fragile materials, pull the switch trigger
gently for low rotation speed (striking force) to achieve optimum results.
8-4. "Rotation Only" and "Rotation + Striking" Changeover Mechanism (DH 25PB only)
The change lever on the Model DH 25PB permits quick and easy changeover between the "Rotation Only" and
"Rotation + Striking" functions.
Armature rotation is transmitted to the first gear, and then to the crank shaft via the two steel balls in the groove of
the first gear. When the change lever is set to the "Rotation Only" position, the eccentric pin of the change lever
pushes up the clutch shaft and the steel balls fall in the groove. Thus the first gear idles on the crank shaft. When
the change lever is returned to the "Rotation + Striking" position, the force of the spring in the crank shaft presses
the clutch shaft back and the steel balls connect the crank shaft hole and the first gear groove to transmit rotation
to the crank shaft.
8-5. "Rotation Only" (no striking) (DH 25PB only)
To use the tool for drilling holes in steel or wood, the chuck adapter and a drill chuck (optional accessories) must
be used. Turn the change lever fully clockwise to the drill mark position to obtain "Rotation Only" function.
Since the Model DH 25PB is equipped with a change lever for changeover between "Rotation Only" and "Rotation
+ Striking" functions, merely mounting the chuck adapter will not stop the striking action; it is absolutely necessary
to turn the change lever to the "Rotation Only" setting for drilling holes in steel or wood. Should the change
lever be set to the "Rotation + Striking" position when the tool is used for drilling, the striking action may
cause the drill chuck to be broken or damaged. Sales personnel should carefully ensure that the buyer is
thoroughly advised on this point.