Hitachi DH 50MB Manual

POWER TOOLS
TECHNICAL DATA
AND
SERVICE MANUAL
HAMMER DRILL
DH 50MB
SPECIFICATIONS AND PARTS ARE SUBJECT TO CHANGE FOR IMPROVEMENT
LIST No. E455 Feb. 2000
D
MODEL
DH 50MB

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
••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
10
6-1. Specification Comparisons ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 10
6-2. Drilling Speed Comparisons •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 11
6-3. Chiseling Performance •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 12
7. PRECAUTIONS IN SALES PROMOTION •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 13
7-1. Handling Instructions ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 13
7-2. Caution Plate •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 13
8. REFERENCES
•••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••
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8-1. Grease Replacement Procedures •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 14
8-2. O-Ring Replacement •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 14
8-3. Structure of the DH 50MB Hammer Drill •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15
[ Service Section ]
9. PRECAUTIONS IN DISASSEMBLYAND REASSEMBLY••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 23
9-1. Disassembly •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 23
9-2. Reassembly •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 24
9-3. Screw Locking Agent TB1401 ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 27
9-4. Tightening Torque •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 27
9-5. Wiring Diagrams •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 28
9-6. Insulation Test •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 28
9-7. No-Load Current Values ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 28
10. STANDARD REPAIR TIME (UNIT) SCHEDULES •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 29
[ Appendix ]
Assembly Diagram for DH 50MB •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 30
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, Model DH 50MB
2. MARKETING OBJECTIVE
The market demand for 50 mm (2") class hammer drills is quickly changing from spline or hexagon bit shank
types to a SDS-MAX bit shank type, especially in the European market. The new Model DH 50MB, which
features the SDS-MAX bit shank, has been developed to meet that market demand.
The main features of the Model DH 50MB are as follows:
1) High drilling speed and impact energy
2) Shock-absorbing handle
3) 2-mode function: Hammer drilling and hammering only
4) Compact and lightweight design
5) Soft-grip handle and side handle
6) Vario Lock mechanism (12 positions)
7) Constant speed with variable speed control
8) Warning display indicating service life of carbon brushes
3. APPLICATIONS
Concrete drilling
Drilling anchor bolt holes
Crushing, chiseling, grooving, edging, cutting, stripping, compacting/tamping and roughing concrete surfaces
[Application examples]
Air conditioning •••••••••••••••• Installation of air conditioners and water coolers
Piping and wiring ••••••••••••• Electric, gas and water supply work
Electric fixtures •••••••••••••••• Installation of electric and lighting fixtures
Sanitary facilities ••••••••••••••Sanitary plumbing
Interior finishing ••••••••••••••• Installation of seats, display counters, ducts and interior decoration
Other building, construction and repair work

--- 2 ---
4. SELLING POINTS
Unique body design
Sealed-grease construction requires minimal maintenance
B : Overall length 595 mm (23-1/2"), Weight 10.8 kg (23.8 lbs.)
C : Overall length 610 mm (24-1/32"), Weight 10.0 kg (22.0 lbs.)
Compact and lightweight: Overall length 495 mm (19-1/2"), Weight 9.8 kg (21.6 lbs.)
Fig. 1
Faster drilling speed
(About 1.8 times faster than the Model DH 40MA)
Change lever for switching between "Rotation +
Hammering" (for drilling), "Neutral" (for positioning the
tool tip) and "Hammering only" (for chiseling and
chipping).
Double insulation construction
Needle-pin type slip clutch
Indication lamp for
carbon brush replacement
Vibration-isolating handle
reduces operator fatigue
Variable speed with constant speed
Vario lock mechanism
Tool angle can be adjusted
easily by using the grip
Soft-touch grip handle
and side handle

--- 3 ---
Speed-adjust dial
Blow (/min.)
Rotation speed (/min.)
Rotation Speed
Blow
3000
2500
2000
1500
1000
350
300
250
200
150
100
12345
4-1. Selling Point Descriptions
4-1-1. Dial type, constant speed electronic control with stepless variable-speed
The Model DH 50MB contains and electronic control circuit which allows the number of revolutions and the
number of strikes to be stepless adjustable from levels 1 to 5 on the dial. The number of revolutions and the
number of strikes are within the range of values in the graph shown below, due to variations of products.
The constant speed control minimizes the change in the number of revolutions or number of strikes at the position
set on the dial even if the load fluctuates, thus providing ease of use and stable drilling efficiency.
Speed-adjust dial
Fig. 2
Fig. 3

--- 4 ---
4-1-2. Faster drilling speed
The drilling speed is 1.8 times faster than that of the Model DH 40MA, as the Model DH 50MB has greater striking
energy owing to the optimized design of the rotation speed, striking frequency and the weight of striker.
4-1-3. Vibration-isolating handle offers less operator fatigue
The two vibration-isolating rubbers provided between the handle and the crank case, and also between the handle
and the housing efficiently absorb the vibration transmitted from the tool main body to minimize transmission of
vibration to the operator's arms.
4-1-4. Indication lamp for carbon brush replacement
The indication lamp will light up (red) approximately 10 hours before the service life of the carbon brushes ends to
notify the operator that the carbon brushes should be replaced with new ones. Replacement of carbon brushes at
the proper time can prevent sudden stop of the motor and result in more efficient operation.
4-1-5. Easy-to-use tool holder
The easy-to-grip tool holder allows the tool to be attached and removed simply by sliding the grip backward.
4-1-6. Soft-touch grip handle and side handle
The double-layer molded handle and side handle consist of a plastic resin base covered with a soft plastic layer to
ensure a soft touch and easy grip of the handles.
4-1-7. Change lever for switching between "rotation + hammering", "neutral" and "hammering only"
The Model DH 50MB provides three functions, "rotation + hammering" function (for drilling), "neutral" function (for
positioning the tool tip) and "hammering only" function (for chiseling and chipping). These function modes can be
easily switched using the change lever located under the cylinder case. This permits accurate centering and
positioning because the function mode can be switched to the hammering only function mode with the drill bit (for
concrete drilling) mounted.
4-1-8. Needle-pin type slip clutch
The Model DH 50MB is equipped with a needle-pin type slip clutch to ensure a greater accuracy of slip torque and
enhanced safety.
Indication lamp for carbon brush
replacement (red)
Vibration-isolating rubber
Vibration-isolating rubber
Handle side

--- 5 ---
5. SPECIFICATIONS
5-1. Specifications
Capacity Drill bit (max. diameter); 50 mm (2"), Core bit (max. diameter); 160 mm (6-1/4")
Power Source
Voltage, current and
power input
Rotation
speed No-load
Full-load
Full-load blow
Type of motor
Type of switch
Type of handle
Enclosure
Dimensions
Weight
Plastic case color
Standard accessories
Net*
Gross
AC single phase 50 Hz or 60 Hz
120 --- 250 /min.
120 --- 250 /min.
1200 --- 2500 /min.
AC single-phase commutator motor
Trigger switch
D-type handle and side handle
Material:
Housing •••••••Glassfiber reinforced polyamide resin (green)
Handle
Handle cover
Crank case cover
495 mm x 293 mm x 120 mm (length x height x width)
(19-1/2" x 11-9/16" x 4-3/4")
9.8 kg (21.6 lbs.)
15.2 kg (33.5 lbs.)
Corrugated cardboard box
Plastic case •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••1
Side handle ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
Hex. bar wrench 4 mm ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
Hex. bar wrench 5 mm ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
Hex. bar wrench 6 mm ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
Stopper ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
Grease (A) •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 1
Voltage (V)
Current (A)
Power input (W)
110 115 127 220 230 240
13.4 12.8 11.6 6.6 6.4 6.2
1400
*: Net weight does not include cord and side handle.
•••••••• Glassfiber reinforced polyamide resin (black and gray)
Packaging
Off-black green
Insulation structure Double insulation

--- 6 ---
5-2. Optional Accessories
1. Drilling work for through-holes (rotation + hammering)
(1) Drill bit (SDS max shank)
+
Drill bit (taper shank)
+
(1) Drill bit (taper shank) (2) Taper shank adapter
(3) Cotter
2. Driling work for anchor holes (rotation + hammering)
+
Outer diameter
(mm) Overall length
(mm) Code No.
313448
313449
313450
313451
313452
313453
313454
313455
340 (13-3/8")
340 (13-3/8")
320 (12-5/8")
320 (12-5/8")
370 (14-9/16")
370 (14-9/16")
370 (14-9/16")
370 (14-9/16")
16 (5/8")
19 (3/4")
22 (7/8")
25 (1")
28 (1-1/8")
32 (1-1/4")
38 (1-1/2")
40 (1-9/16")
Outer diameter
(mm) Overall length (mm) Code No.
313456
313457
313458
313459
313460
313461
313462
313463
540 (21-1/4")
540 (21-1/4")
520 (20-15/32")
520 (20-15/32")
570 (22-7/16")
570 (22-7/16")
570 (22-7/16")
570 (22-7/16")
16 (5/8")
19 (3/4")
22 (7/8")
25 (1")
28 (1-1/8")
32 (1-1/4")
38 (1-1/2")
40 (1-9/16")
(1) Drill bit (taper shank)
Outer diameter(mm) Code No.
944463
Taper dimension
Morse taper No. 1
Code No.
313464
Code No.
944477
(3) Cotter(2) Taper shank adapter
11 (7/16")
12.3 (15/32")
12.7 (1/2")
14.3 (9/16")
14.5 (9/16")
17.5 (11/16")
944460
944461
993038
944462
944500

--- 7 ---
(1) Guide plate
Core bits with outer diameter of 32, 35, 38, 45, 50, 54, 60, 64, 70, 75, 79, 94, 100, 105, 120, 150 mm (1-1/4",
1-3/8", 1-1/2", 1-3/4", 2", 2-1/8", 2-3/8", 2-1/2", 2-3/4", 2-15/16", 3-1/8", 3-11/16", 3-15/16", 4-1/8", 4-3/4", 6")
[Guide plate is not used with core bits with outer diameter of 25 mm (1") and 29 mm (1-1/8")]
(2) Center pin
for core bits with outer diameter of 32, 35 mm (1-1/4", 1-3/8")
for core bits with outer diameter of 38, 45, 50, 54, 60, 64, 70, 75, 79, 94,100, 105, 120, 150 mm
(1-1/2", 1-3/4", 2", 2-1/8", 2-3/8", 2-1/2", 2-3/4", 2-15/16", 3-1/8", 3-11/16", 3-15/16", 4-1/8", 4-3/4", 6")
[Center pin is not used with core bits of 25 mm (1") and 29 mm (1/8")]
(3) Core bit
Code No. 956009
Code No. 955165
(1) Drill bit (SDS-plus shank)
+
(2) SDS-plus shank
bit adapter
3. Boring work for large-diameter holes (rotation + hammering)
(1) Guide plate (2) Center pin (3) Core bit (4) Core bit shank
+
+
+
Outer diameter (mm) Code No. Outer diameter (mm) Code No.
25 (1") 955994 75 (2-15/16") 959709
29 (1-1/8") 955995 79 (3-1/8") 955157
32 (1-1/4") 955996 94 (3-11/16") 956004
35 (1-3/8") 955998 100 (3-15/16") 959710
38 (1-1/2") 956000 105 (4-1/8") 955159
45 (1-3/4") 955154 120 (4-3/4") 956006
50 (2") 959706 150 (6") 956728
54 (2-1/8") 955155
60 (2-3/8") 959707
64 (2-1/2") 956002
70 (2-3/4") 959708
(4) Core bit shank
for core bits with outer diameter of 25, 29, 32, and 35 mm (1", 1-1/8", 1-1/4", and 1-3/8")
for core bits with outer diameter of 38, 45, 50, 54, 60, 64, 70, 75, 79, 94, 100, 105, 120, 150 mm
(1-1/2", 1-3/4", 2", 2-1/8", 2-3/8", 2-1/2", 2-3/4", 2-15/16", 3-1/8", 3-11/16", 3-15/16", 4-1/8", 4-3/4", 6")
Code No. 313465
SDS-plus shank bit adapter
+ +
Code No. 313466
Code No. 313467

--- 8 ---
+
4. Hole drilling •••••• For drilling steel and wood
++
(1) 13 mm (1/2") drill chuck
(13VLA) (2) Chuck adapter
(3) Chuck wrench
5. Chemical anchor hole drilling work (rotation + hammering)
++
+
(Socket) (1) Chemical anchor adapter
6. Demolition work (hammering)
(1) Bull point
7. Grooving and edging (hammering)
(1) Cold chisel
(1) 13 mm (1/2") drill chuck (13VLA)
Code No. 950272
(2) Chuck adapter (3) Chuck wrench
Code No. 313468 Code No. 930515
12.7 mm (1/2")
19.0 mm (3/4")
Socket square size Code No.
313469
313470
280 mm (11")
400 mm (15-3/4")
Overall length Code No.
313471
313472
280 mm (11")
400 mm (15-3/4")
Overall length Code No.
313473
313474

--- 9 ---
(1) Cutter
+
8. Cutting and stripping (asphalt cutting, etc.) (hammering)
9. Digging (substitute pick-ax) (hammering)
+
(1) Scoop
11. Tamping work (hammering)
10. Surface roughing work (hammering)
Code No. 313477
(1) Bushing tool (2) Shank
++
+
+
(1) Rammer (2) Shank
Code No. 313478
150 mm x 150 mm
50 mm (2") 400 mm (15-3/4")
Width Code No.
313475
Overall length
220 mm (8-21/32") Code No.
313479
Overall length
400 mm (15-3/4") Code No. 313476
Overall length
220 mm (8-21/32") Code No. 313479
Overall length

--- 10 ---
Maker, Model
Capacity
No-load (/min.)
Full-load (/min.)
Full-load blow (/min.)
Insulation structure
Full-load vibration level (dB)
No-load sound pressure
level (dB/A)
Weight
(kg)*
Overall length (mm)
Height (mm)
Width (mm)
Drill bit dia. (mm)
Power input (W)
Power output (W)
Core bit dia. (mm)
Item
Rotation
speed
Dimensions
Double insulation
50 (2")
160 (6-1/4")
120 --- 250
1400
1200 --- 2500
HITACHI
DH 50MB
120
495 (19-1/2")
293 (11-9/16")
120 (4-3/4")
9.8 (21.6 Ibs.)
87
120 --- 250
Double insulation
52 (2")
150 (6")
120 --- 250
1500
1100 --- 2250
B
120
595 (23 -1/2")
280 (11-1/32")
128 (5-1/16")
10.8 (23.8 Ibs.)
85
120 --- 250
Double insulation
37 (1-7/16")
160 (6-1/4")
0 --- 255
1050
0 --- 2700
D
119
495 (19-1/2")
259 (10-7/32")
115 (4-17/32")
7.9 (17.4 Ibs.)
84
0 --- 255
12. Syringe (for chip removal)
Code No. 944575
500 g can
Code No. 980927
30 g tube
Code No. 981840
70 g tube
Code No. 308471
13. Impact drill grease
Note: Code numbers listed above are subject to change without notice.
Please refer to periodic Technical News Bulletins for updates.
6. COMPARISONS WITH SIMILAR PRODUCTS
6-1. Specification Comparisons
*Weight does not include cord and side handle.
Catalog weight
Actual weight 10.3 (21.6 Ibs.) 10.8 (23.8 Ibs.) N/A

--- 11 ---
6-2. Drilling Speed Comparisons
Drilling speed varies considerably depending on the work conditions. Use the factory test results shown in Fig. 4
as a reference, for comparison purposes only.
Fig. 4
0100 200 300 400 500
DH 50MB
B
D
DH 50MB
B
D
DH 50MB
B
D
DH 50MB
B
D
DH 50MB
B
D
DH 50MB
B
D
DH 50MB
B
D
DH 50MB
B
D
HITACHI
B
D
HITACHI
B
D
HITACHI
B
D
HITACHI
B
D
HITACHI
B
D
HITACHI
B
D
HITACHI
B
D
HITACHI
B
D
φ16
φ19
φ22
φ25
φ28
φ32
φ38
φ40
480
380
340
430
320
290
275
250
290
225
370
225
240
190
190
160
130
120
110
110
75 *
60 *
90
90
Drill bit dia.
(mm) Maker Model Drilling speed (mm/min.)
*: Note that the data marked with asterisks are test results using drill bits which are beyond the tool's rated capacity. Use the
above data as a reference, for comparison purposes only.
[Test conditions]
Orientation : Downward drilling
Pressing force : 10 kgf
Test material : Concrete panel with a compression strength of 240 kgf/cm2
Drill bit size : SDS-max shank drill bit

--- 12 ---
Voltage
supply
230 V
Maker Model
HITACHI DH 50MB
BB
DD
050 100 150 200 250
150
145
90
Demolished amount (kg/30 min.)
6-3. Chiseling Performance
Chiseling performance varies considerably depending on the work conditions. Use these factory test results
shown in Fig. 5 for comparison purposes only.
Fig.5
[Test conditions]
Orientation : Downward chiseling
Test material : Concrete panel with a compression strength of 2,919 N/cm2(240 kgf/cm2)
Bull point : SDS-max shank bull point of 280 mm

--- 13 ---
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 Model DH 50MB Hammer Drill 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
Each Model DH 50MB unit is provided with a Caution Plate (illustrated below) which lists basic safety precautions
for its use. Carefully ensure that the customer fully understands and follows these precautions before using the
tool.
(1) For Australia, New Zealand and China
(2) For the U.S.A. and Canada
(3) For Taiwan
WARNING
To reduce the risk of injury, user must read and
understand instruction manual.
AVERTISSEMENT
Afin de reduire le risque de blessures, l'utilisateur doit
lire et bien comprendre le mode d'emploi.

--- 14 ---
8. REFERENCES
8-1. Grease Replacement Procedures
The electro-pneumatic hammering section and gear change section each use different kinds of grease.
It is not necessary to replenish the grease unless the tool is disassembled for repair or there is a 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 re-lube with 30 g in the Cylinder Case and
75 g in the Crank Case (on the Connecting Rod side). Take care not to overfill with grease as an excessive
amount of grease can cause hammering failure.
The gear change section (in the Gear Cover) uses grease No. 29 for power tools. Lube with 40 g of this grease.
Do not use the special grease used for the hammering section, or it will leak to the motor parts resulting in 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 its 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 50MB Hammer Drill
Grip Bevel
gear
Cylinder
Needle
holder
Second
hammer Striker Air
chamber
Key Piston Connecting rod
Crank shaftFirst gear
Needle
roller
Retainer
sleeve
O-ring
Second gear
Bevel pinion
Armature
Key slot
Fig. 6
Torque transmission
Rotation transmission is described below with reference to Fig. 6. The gear arrangement of the Model
DH 50MB has the armature shaft positioned between the crank shaft and bevel pinion shaft. Rotation of the
armature shaft is transmitted to the second gear through the first gear of the crank shaft and the second
pinion. Then the rotation is transmitted from the second gear through the slip mechanism disposed between
the second gear and the bevel pinion shaft to turn the bevel gear. The bevel gear is keyed to the cylinder
through the clutch to rotate together. Rotation of the cylinder is transmitted to the retainer sleeve coupled
together by means of four needle pins, and then to the drill bit inserted into the retainer sleeve by way of three
key slots and two needle rollers which couple them together.
Hammering
Armature rotation is transmitted to the crank and connecting rod so that the piston moves reciprocally within
the cylinder. Air pressure developing between the piston and the striker changes with movement of the piston.
The internal pressure thus pushes the striker to repeatedly strike the end face of the second hammer. Since
the striker is moved by means of air pressure, the cushioning effect of the air absorbs the hammering shock
experienced by the operator. If air leaks from the air pressure chamber, the cushioning effect will not be
enough to absorb shock. O-rings fitted around the striker and piston for air sealing therefore play an important
role for the intended function of this hammer drill.
Handle
Needle
pin
Clutch

--- 16 ---
Switching between "Drill + Hammering", "Neutral" and "Hammering only"
Fig. 7
The shanks of the SDS max type working tools are all
of the same shape for drill bits, bull points for chiseling
and chipping and cold chisels. When chiseling and
chipping with this hammer drill, it is necessary to stop
the drilling motion and choose the "Hammering only"
mode by means of the change lever to lock the working
tool against rotation.
The change lever mechanism is described below with
reference to Figs. 7, 8 and 9.
Fig. 7 is a cross-sectional view showing the "Rotation +
Hammering" mode, in which the bevel gear dog meshes
with the clutch dog to transmit rotation to the cylinder
keyed to the clutch, so as to rotate the working tool.
Fig. 8 is a sectional view showing the "Neutral" mode, in
which, with the change lever turned 90˚, the bevel gear
is brought out of engagement with the clutch to cut off
power transmission. In this position, the tool holder grip
can be manually turned to enable easier positioning of
the working tool for chiseling and chipping.
Fig. 9 is likewise a sectional view showing the
"Hammering only" mode. With the change lever turned
another 90˚, the clutch comes into mesh with the lock
sleeve, and the splines on the outer circumference of
the lock sleeve come into mesh with the splines on the
internal face of the cylinder case, so that the cylinder as
well as the working tool are prevented from rotating.
Since this hammer drill has three switchable modes as
mentioned above, serious accidents may result if a tool
for chipping or chiseling should be used in the
"Rotation + Hammering" mode. Ensure that your
customers are advised to always use the "Hammering"
mode when doing chiseling or chipping work.
Fig. 9
Fig. 8
Lock sleeve Clutch
Change lever
Bevel gear
Cylinder
Lock sleeve Clutch
Change lever
Bevel gear
Cylinder
Lock sleeve Clutch
Change lever
Bevel gear
Cylinder

--- 17 ---
Mechanism to prevent idle hammering
The arrangement against idle hammering of this hammer drill is about the same as for the DH 40MA/MB in
which, when the drill bit or bull point is no longer pressed against the concrete or similar material, the second
hammer moves to a position shown in Fig. 10 so that the striker is displaced from its hammering position. This
opens the air vent so that the piston movement causes no change in air pressure in the pressure chamber,
thus stopping the hammering action.
Slip mechanism
The slip mechanism is described below with reference to Fig. 11. The bevel pinion and the gear holder are
coupled together by the key and press-fitting. The springs (C) and the needle pins are housed in elongated
grooves of the gear holder. The needle pin is pressed against the inner face of the second gear by the springs
(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 the
springs (C) to allow idle rotation of the second gear. With this 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.
Second hammer Striker
Travel distance of the second hammer Air vent
Pressure chamber
Fig. 10
Bevel pinion
Fig. 11
Elongated grooves
of the gear holder
Needle pin
Key
Spring (C)
Bevel pinion
Gear holder
Second gearGear holder
Section A-A
AA

--- 18 ---
Fig. 12
Drill bit
As illustrated in Fig. 12, the tool holder is designed to accept SDS max shank bits so that torque transmission
to the drill bit is accomplished with three key rails formed on the tool holder, with two needle rollers provided to
prevent the drill bit from slipping out.
The round shank, with an outer diameter of 18 mm, tends to attract less dust to itself or to the hammer drill
itself. Also, the runout of drill bit becomes less by making the guide length of the shank longer.
A
A
Key slot
Dia. 18 mm
Key rail (3 pieces)
Needle roller
(2 pieces) Retainer sleeve
Needle holder
Key slot
Cross section A-A
Tool holder cross section