Drill Master 3670 Installation manual

3/8” VARIABLE SPEED
REVERSIBLE DRILL
Model 3670
SET UP AND OPERATING INSTRUCTIONS
Visit our website at: http://www.harborfreight.com
Read this material before using this product.
Failure to do so can result in serious injury.
SAVE THIS MANUAL.
Copyright©2003 by Harbor Freight Tools®. All rights reserved. No portion of this manual or any artwork
contained herein may be reproduced in any shape or form without the express written consent of
Harbor Freight Tools. Diagrams within this manual may not be drawn proportionally. Due to continuing
improvements, actual product may differ slightly from the product described herein. Tools required for
assembly and service may not be included.
For technical questions or replacement parts, please call 1-800-444-3353.
Manual revised 10g

Page 2For technical questions, please call 1-800-444-3353.SKU 3670
SAVE THIS MANUAL
Keep this manual for the safety warnings
and precautions, assembly, operating,
inspection, maintenance and cleaning
procedures. Write the product’s serial number
in the back of the manual near the assembly
diagram (or month and year of purchase if
product has no number). Keep this manual
and the receipt in a safe and dry place for
future reference.
IMPORTANT SAFETY
INFORMATION
In this manual, on the labeling, and
all other information provided with
this product:
This is the safety alert
symbol. It is used to alert
you to potential personal
injury hazards. Obey all
safety messages that follow
this symbol to avoid possible
injury or death.
DANGER indicates a
hazardous situation
which, if not avoided, will result
in death or serious injury.
WARNING indicates a
hazardous situation
which, if not avoided, could
result in death or serious injury.
CAUTION, used with
the safety alert
symbol, indicates a hazardous
situation which, if not avoided,
could result in minor or moderate
injury.
NOTICE is used to
address practices not
related to personal injury.
CAUTION, without the
safety alert symbol, is
used to address practices not
related to personal injury.
General Power Tool Safety Warnings
WARNING Read all safety warnings
and instructions. Failure to follow the
warnings and instructions may result
in electric shock, re and/or serious
injury.
Save all warnings and instructions
for future reference.
The term ″power tool″ in the warnings
refers to your mains-operated (corded)
power tool or battery-operated
(cordless) power tool.
1. Work area safety
a. Keep work area clean and well lit.
Cluttered or dark areas invite accidents.
b. Do not operate power tools in
explosive atmospheres, such as in
the presence of ammable liquids,
gases or dust. Power tools create
sparks which may ignite the dust or
fumes.
c. Keep children and bystanders
away while operating a power tool.
Distractions can cause you to lose
control.
2. Electrical safety
a. Power tool plugs must match the
outlet. Never modify the plug in
any way. Do not use any adapter
plugs with grounded power tools.
Unmodied plugs and matching outlets
will reduce risk of electric shock.
b. Avoid body contact with grounded
surfaces such as pipes, radiators,

Page 3For technical questions, please call 1-800-444-3353.SKU 3670
ranges and refrigerators. There is an
increased risk of electric shock if your
body is grounded.
c. Do not expose power tools to rain
or wet conditions. Water entering
a power tool will increase the risk of
electric shock.
d. Do not abuse the cord. Never use
the cord for carrying, pulling or
unplugging the power tool. Keep
cord away from heat, oil, sharp
edges or moving parts. Damaged
or entangled cords increase the risk of
electric shock.
e. When operating a power tool
outdoors, use an extension cord
suitable for outdoor use. Use of a
cord suitable for outdoor use reduces
the risk of electric shock.
f. If operating a power tool in a damp
location is unavoidable, use a
Ground Fault Circuit Interrupter
(GFCI) protected supply. Use of a
GFCI reduces the risk of electric shock.
3. Personal safety
a. Stay alert, watch what you are
doing and use common sense when
operating a power tool. Do not use
a power tool while you are tired or
under the inuence of drugs, alcohol
or medication. A moment of inattention
while operating power tools may result
in serious personal injury.
b. Use personal protective equipment.
Always wear eye protection. Safety
equipment such as dust mask, non-
skid safety shoes, hard hat, or hearing
protection used for appropriate
conditions will reduce personal injuries.
c. Prevent unintentional starting.
Ensure the switch is in the off-
position before connecting to power
source and/or battery pack, picking
up or carrying the tool. Carrying
power tools with your nger on the
switch or energizing power tools that
have the switch on invites accidents.
d. Remove any adjusting key or wrench
before turning the power tool on.
A wrench or a key left attached to a
rotating part of the power tool may result
in personal injury.
e. Do not overreach. Keep proper
footing and balance at all times. This
enables better control of the power tool
in unexpected situations.
f. Dress properly. Do not wear loose
clothing or jewelry. Keep your hair,
clothing and gloves away from
moving parts. Loose clothes, jewelry
or long hair can be caught in moving
parts.
g. If devices are provided for the
connection of dust extraction and
collection facilities, ensure these are
connected and properly used. Use of
these devices can reduce dust-related
hazards.
h. Only use safety equipment that has
been approved by an appropriate
standards agency. Unapproved
safety equipment may not provide
adequate protection. Eye protection
must be ANSI-approved and breathing
protection must be NIOSH-approved for
the specic hazards in the work area.
4. Power tool use and care
a. Do not force the power tool. Use
the correct power tool for your
application. The correct power tool will
do the job better and safer at the rate
for which it was designed.
b. Do not use the power tool if the
switch does not turn it on and off.
Any power tool that cannot be controlled

Page 4For technical questions, please call 1-800-444-3353.SKU 3670
with the switch is dangerous and must
be repaired.
c. Disconnect the plug from the power
source and/or the battery pack from
the power tool before making any
adjustments, changing accessories,
or storing power tools. Such
preventive safety measures reduce
the risk of starting the power tool
accidentally.
d. Store idle power tools out of the
reach of children and do not allow
persons unfamiliar with the power
tool or these instructions to operate
the power tool. Power tools are
dangerous in the hands of untrained
users.
e. Maintain power tools. Check for
misalignment or binding of moving
parts, breakage of parts and any
other condition that may affect the
power tool’s operation. If damaged,
have the power tool repaired before
use. Many accidents are caused by
poorly maintained power tools.
f. Keep cutting tools sharp and clean.
Properly maintained cutting tools with
sharp cutting edges are less likely to
bind and are easier to control.
g. Use the power tool, accessories
and tool bits etc. in accordance
with these instructions, taking into
account the working conditions and
the work to be performed. Use of
the power tool for operations different
from those intended could result in a
hazardous situation.
5. Service
a. Have your power tool serviced by a
qualied repair person using only
identical replacement parts. This will
ensure that the safety of the power tool
is maintained.
Drill Safety Warnings
1. Hold Drill by insulated gripping
surfaces when performing an
operation where the Drill may contact
hidden wiring or its own cord.
Contact with a “live” wire will make
exposed metal parts of the Drill “live” and
shock the operator.
2. Maintain labels and nameplates on
the tool. These carry important safety
information. If unreadable or missing,
contact Harbor Freight Tools for a
replacement.
3. Avoid unintentional starting. Prepare to
begin work before turning on the tool.
4. Do not lay the tool down until it has come
to a complete stop. Moving parts can
grab the surface and pull the tool out of
your control.
5. When using a handheld power tool,

hands to resist starting torque.
6. Do not leave the tool unattended when
it is plugged into an electrical outlet.
Turn off the tool, and unplug it from its
electrical outlet before leaving.
7. This product is not a toy. Keep it out of
reach of children.
8. People with pacemakers should
consult their physician(s) before use.

to heart pacemaker could cause
pacemaker interference or pacemaker
failure. In addition, people with
pacemakers should:


on.

electrical shock.


Page 5For technical questions, please call 1-800-444-3353.SKU 3670
grounded. Ground Fault Circuit
Interrupter (GFCI) should also be
implemented – it prevents sustained
electrical shock.
9. WARNING: Some dust created by power
sanding, sawing, grinding, drilling, and
other construction activities, contains
chemicals known [to the State of
California] to cause cancer, birth defects
or other reproductive harm. Some
examples of these chemicals are:


cement or other masonry products

treated lumber
Your risk from these exposures varies,
depending on how often you do this type
of work. To reduce your exposure to
these chemicals: work in a well ventilated
area, and work with approved safety
equipment, such as those dust masks

microscopic particles. (California Health
& Safety Code § 25249.5, et seq.)
10. WARNING: Handling the cord on this
product will expose you to lead, a
chemical known to the State of California
to cause cancer, and birth defects or
other reproductive harm. Wash hands
after handling. (California Health &
Safety Code § 25249.5, et seq.)
11. The warnings, precautions, and
instructions discussed in this instruction
manual cannot cover all possible
conditions and situations that may occur.
It must be understood by the operator
that common sense and caution are
factors which cannot be built into this
product, but must be supplied by the
operator.
Vibration Safety
This tool vibrates during use. Repeated

cause temporary or permanent physical
injury, particularly to the hands, arms
and shoulders. To reduce the risk of

1. Anyone using vibrating tools regularly

be examined by a doctor and then have

medical problems are not being caused
or worsened from use. Pregnant
women or people who have impaired
blood circulation to the hand, past hand
injuries, nervous system disorders,
diabetes, or Raynaud’s Disease
should not use this tool. If you feel any
symptoms related to vibration (such as
tingling, numbness, and white or blue

possible.
2. Do not smoke during use. Nicotine
reduces the blood supply to the hands


3. Wear suitable gloves to reduce the
vibration effects on the user.
4. Use tools with the lowest vibration when
there is a choice.
5. 
of work.
6. Grip tool as lightly as possible (while still

do the work.
7. To reduce vibration, maintain the tool
as explained in this manual. If any
abnormal vibration occurs, stop use
immediately.

Page 6For technical questions, please call 1-800-444-3353.SKU 3670
SAVE THESE
INSTRUCTIONS.
GROUNDING
TO PREVENT
ELECTRIC SHOCK
AND DEATH FROM INCORRECT
GROUNDING WIRE
CONNECTION:
Check with a qualied electrician
if you are in doubt as to whether
the outlet is properly grounded.
Do not modify the power cord
plug provided with the tool.
Never remove the grounding
prong from the plug. Do not use
the tool if the power cord or plug
is damaged. If damaged, have it
repaired by a service facility
before use. If the plug will not t
the outlet, have a proper outlet
installed by a qualied
electrician.
Grounded Tools: Tools with Three
Prong Plugs
3-Prong Plug and Outlet
1. Tools marked with “Grounding Required”
have a three wire cord and three prong
grounding plug. The plug must be
connected to a properly grounded outlet.
If the tool should electrically malfunction
or break down, grounding provides a
low resistance path to carry electricity
away from the user, reducing the risk of
electric shock. (See 3-Prong Plug and
Outlet.)
2. The grounding prong in the plug is
connected through the green wire inside
the cord to the grounding system in the
tool. The green wire in the cord must
be the only wire connected to the tool’s
grounding system and must never be
attached to an electrically “live” terminal.
(See 3-Prong Plug and Outlet.)
3. The tool must be plugged into an
appropriate outlet, properly installed and
grounded in accordance with all codes
and ordinances. The plug and outlet
should look like those in the preceding
illustration. (See 3-Prong Plug and
Outlet.)
Double Insulated Tools: Tools with
Two Prong Plugs
Outlets for 2-Prong Plug
1. Tools marked “Double Insulated” do not
require grounding. They have a special

OSHA requirements and complies with
the applicable standards of Underwriters

Standard Association, and the National
Electrical Code.
2. Double insulated tools may be used in
either of the 120 volt outlets shown in the
preceding illustration. (See Outlets for
2-Prong Plug.)

Page 7For technical questions, please call 1-800-444-3353.SKU 3670
Extension Cords
1. Grounded tools require a three wire
extension cord. Double Insulated
tools can use either a two or three wire
extension cord.
2. As the distance from the supply outlet
increases, you must use a heavier gauge
extension cord. Using extension cords
with inadequately sized wire causes a
serious drop in voltage, resulting in loss
of power and possible tool damage.
(See Table A.)
3. The smaller the gauge number of the
wire, the greater the capacity of the cord.
For example, a 14 gauge cord can carry
a higher current than a 16 gauge cord.
(See Table A.)
4. When using more than one extension
cord to make up the total length, make
sure each cord contains at least the
minimum wire size required. (See Table
A.)
5. If you are using one extension cord for
more than one tool, add the nameplate
amperes and use the sum to determine
the required minimum cord size. (See
Table A.)
6. If you are using an extension cord
outdoors, make sure it is marked with the

is acceptable for outdoor use.
7. Make sure the extension cord is properly
wired and in good electrical condition.
Always replace a damaged extension

electrician before using it.
8. Protect the extension cords from sharp
objects, excessive heat, and damp or
wet areas.
RECOMMENDED MINIMUM WIRE GAUGE
FOR EXTENSION CORDS* (120/240 VOLT)
NAMEPLATE
AMPERES
(at full load)
EXTENSION CORD
LENGTH
25’ 50’ 75’ 100’ 150’
0 – 2.0 18 18 18 18 16
2.1 – 3.4 18 18 18 16 14
3.5 – 5.0 18 18 16 14 12
5.1 – 7.0 18 16 14 12 12
7.1 – 12.0 18 14 12 10 
12.1 – 16.0 14 12 10  
16.1 – 20.0 12 10 
TABLE A
* Based on limiting the line volt-
age drop to ve volts at 150% of
the rated amperes.
Symbology
Double Insulated
Canadian Standards Association

V~ Volts Alternating Current
AAmperes
n0xxxx/min. 
(RPM)

Page 8For technical questions, please call 1-800-444-3353.SKU 3670
SPECIFICATIONS
Electrical Input 120 V~ / 60 Hz / 3.1 A
Motor Speed 
Chuck Capacity 1/16” to 3/8”
Chuck Type Keyless
3150240
UNPACKING
When unpacking, make sure that the
item is intact and undamaged. If any parts
are missing or broken, please call Harbor

possible.
INSTRUCTIONS FOR PUTTING
INTO USE
Read the ENTIRE IMPORTANT
SAFETY INFORMATION
section at the beginning of this
manual including all text under
subheadings therein before set up
or use of this product.
TO PREVENT
SERIOUS INJURY
FROM ACCIDENTAL
OPERATION:
Turn the Power Switch of the tool
off and unplug the tool from its
electrical outlet before
assembling or making any
adjustments to the tool.
Note: For additional information regarding the
parts listed in the following pages, refer
to the Assembly Diagram near the end of
this manual.
Functions
1.
Figure 1
Forward/
Reverse Switch
(30)

Dial (31) Trigger
(32)

The Trigger can be locked in the ON
position for extended operation.
See Figure 1.
2. The Keyless Chuck allows the operator
to install and remove drill bits without
using a key or tools.
OPERATING INSTRUCTIONS
Read the ENTIRE IMPORTANT
SAFETY INFORMATION
section at the beginning of this
manual including all text under
subheadings therein before set up
or use of this product.
Tool Set Up
TO PREVENT
SERIOUS INJURY
FROM ACCIDENTAL
OPERATION: Release the Trigger
(32) and disconnect from power
source before adjusting tool or
installing a drill bit.
1. To insert a drill bit, hold the rear ring
of the Chuck (5) with one hand while
turning the front end clockwise with the
other hand to open the jaws.
Rev 10g, 12c

Page 9For technical questions, please call 1-800-444-3353.SKU 3670
2. Open the jaws enough to allow the bit to
slide into the Chuck. Turn the front ring
counterclockwise to tighten the jaws on
the bit shank.
3. CAUTION! 


bit to make sure it is securely attached.
4. WARNING! Do not use dull or damaged
bits. Doing so can cause undue stress
on the Drill, leading to possible property
damage and/or personal injury.
Work Piece and Work Area Set Up
1. Designate a work area that is clean and

access by children or pets to prevent
distraction and injury.
2. Route the power cord along a safe
path to reach the work area without
creating a tripping hazard or exposing
the power cord to possible damage. The
power cord must reach the work area
with enough extra length to allow free
movement while working.
3. Secure loose work pieces using a vise
or clamps (not included) to prevent
movement while working.
4. There must not be objects, such as utility
lines, nearby that will present a hazard
while working.
General Operating Instructions
1. Plug Power Cord (21) into suitable outlet.
2. Use the Forward/Reverse Switch (30)
above the Trigger (32) to determine the
rotation direction of the Chuck. Slide it to
the right side for reverse Chuck rotation.
Slide to the left side for forward Chuck
rotation. See Figure 1. CAUTION! Allow
Chuck to come to complete stop prior to
changing its direction of rotation.
3. Squeeze the Trigger (32) to start the
tool. The Trigger has a variable speed
feature. Pressing it lightly will make the

cause the tool to operate faster.

to limit the travel of the Trigger. Turning

Trigger movement to low speed settings.
Turning the dial clockwise (+) will allow
for full Trigger range and faster speeds.
4. To lock the Trigger in the ON position,
squeeze the Trigger, pressing in the

the Trigger. The tool will operate
continuously. To stop the tool, squeeze
and release the Trigger.
5. To prevent accidents, turn off the tool
and disconnect from power source after
use. Clean, then store the tool indoors
out of children’s reach.
The Drilling Operation
1. 
good condition and appropriate to task.
2. 
not press too hard. Too much pressure
will not help the process and will cause
bit to overheat, may cause bit to bend or
break, cause undue strain on the tool,
and may damage the bit or work piece.
Pressing too hard may stall the motor.
3. WARNING! If motor stalls, release
Trigger immediately to prevent damage
to the tool.
4. 

bit while drilling may cause the bit to
Rev 10g

Page 10For technical questions, please call 1-800-444-3353.SKU 3670
bend or break and may damage the work
piece.
5. 
about to penetrate the work piece.
6. Keep the motor running when pulling the
bit out of a completed hole to prevent the
bit from jamming.
Metal Drilling
1. Use high speed steel, carbide or
specialty bits for metal drilling.
2. Secure the work piece to keep it from
moving during the drilling operation.
3. Use a punch to create a dimple for the
bit to start.
4. Start by drilling slowly to keep bit from
moving away from your starting point.
5. As the hole is established, increase tool
speed. Do not go so fast or use so much
pressure that the bit heats up. This can
damage the bit and create an irregular
hole. For hard metal or thick pieces, use
cutting oil to keep the bit cool.
6. Since drilling in metal is a slow operation,
you may lock the Trigger in the ON
position to maintain a constant speed
and reduce fatigue.
7. When drilling large holes in metal, start
by drilling a smaller pilot hole, then using

Wood Drilling
1. Use high carbon bits or bits specially
designed for wood drilling, such as brad
point, spade bits, forstner bits, etc.
2. Secure the work piece to keep it from
moving during the drilling operation.
3. Start by drilling slowly to keep the bit
from moving away from your starting
point. Increase speed as the hole is
established.
4. To prevent or reduce “break out” when
the bit penetrates the work piece, clamp
a piece of scrap material to the back of
the work piece.
5. Do not lock the Trigger in the ON
position, as the bit can easily jam in
wood and the motor must be stopped
quickly.
MAINTENANCE AND
SERVICING
Procedures not specically
explained in this manual must
be performed only by a qualied
technician.
TO PREVENT
SERIOUS INJURY
FROM ACCIDENTAL
OPERATION:
Turn the Power Switch of the tool
off and unplug the tool from its
electrical outlet before
performing any inspection,
maintenance, cleaning
procedures, or removing/
attaching bits.
TO PREVENT SERIOUS INJURY
FROM TOOL FAILURE:
Do not use damaged equipment.
If abnormal noise or vibration
occurs, have the problem
corrected before further use.
Cleaning, Maintenance, and
Lubrication
1. BEFORE EACH USE, inspect the
general condition of the tool. Check for

Page 11For technical questions, please call 1-800-444-3353.SKU 3670
Troubleshooting
Problem Possible Causes Likely Solutions
Tool will not start. 1. Cord not connected.
2. No power at outlet.
3. Internal damage or wear.
(Carbon brushes or switch, for
example.)
1. Check that cord is plugged in.
2. Check power at outlet. If outlet is unpowered,
turn off tool and check circuit breaker. If breaker
is tripped, make sure circuit is right capacity for
tool and circuit has no other loads.
3. Have technician service tool.
Tool operates slowly. 1. Extension cord too long or wire
size too small.
2. Applying too much pressure.
1. Eliminate use of extension cord. If an extension
cord is needed, use shorter/heavier gauge cord.
See Extension Cords in GROUNDING section.
2. 
torque setting to it minimum.
Performance
decreases over time.
1. Accessory dull or damaged.
2. Carbon brushes worn or
damaged.
1. Keep cutting accessories sharp. Replace as
needed.
2. 
Excessive noise or
rattling.
Internal damage or wear. (Carbon
brushes or bearings, for example.)
Have technician service tool.
Overheating. 1. Forcing tool to work too fast.
2. Accessory misaligned.
3. Accessory dull or damaged.
4. 
5. Motor being strained by long or
small diameter extension cord.
1. Allow tool to work at its own rate.
2. Check and correct accessory to fence and/or
table alignment.
3. Keep cutting accessories sharp. Replace as
needed.
4. 
approved dust mask/respirator while blowing dust
out of motor using compressed air.
5. Eliminate use of extension cord. If an extension
cord is needed, use one with the proper diameter
for its length and load. See Extension Cords in
GROUNDING section.
Follow all safety precautions whenever diagnosing or servicing the tool.
Disconnect power supply before service.
loose hardware, misalignment or binding
of moving parts, cracked or broken parts,
damaged electrical wiring, and any
other condition that may affect its safe
operation.
2. AFTER USE, wipe external surfaces
of the tool with clean cloth. Do not use
solvents.
3. Inspect the Chuck and remove any dirt
or debris.
4. PERIODICALLY check the Mounting
Screws (3) and tighten if necessary.
5. 
Harbor Freight Tools for replacements

replace them.
6. WARNING! If the supply cord of
this power tool is damaged, it must be
replaced only by a qualied service
technician.

Page 12For technical questions, please call 1-800-444-3353.SKU 3670
Part Description Qty.
2 1
3 Mounting Screw (M5 x 22) 1
4 Spring Washer 1
5 Chuck 1
6 Spindle 1
7 Half Circle Key 1
8 1
9 Gear 1
10 Fender Ring 1
11  1
12  1
13 Armature 1
14  2
15  2
16  1
17 Stator 1
Part Description Qty.
18 Clip 1
19 Self Tapping Screw (4 x 12) 2
20 Cable Sheath 1
21 Power Cord and Plug 1
22 Switch Module 1
23  2
24  2
25  2
26 Right Motor Housing 1
27 Screw (4 x 16) 2
28 Screw (4 x 20) 6
29  1
30 Forward/Reverse Switch 1
31 Torque Adjusting Knob 1
32 Trigger 1
PLEASE READ THE FOLLOWING CAREFULLY









PARTS LIST
Record Product’s Serial Number Here:
Note: If product has no serial number, record month and year of purchase instead.
Note: Some parts are listed and shown for illustration purposes only, and are not available
individually as replacement parts.

Page 13For technical questions, please call 1-800-444-3353.SKU 3670
ASSEMBLY DIAGRAM
2
3
4
5
67
8
9
11
10
12
13
14
15
16
17
22 23
25
24
19
18
21
20
27
26
28
29
30
31
32

Page 14For technical questions, please call 1-800-444-3353.SKU 3670
LIMITED 90 DAY WARRANTY
Harbor Freight Tools Co. makes every effort to assure that its products meet high quality and
durability standards, and warrants to the original purchaser that this product is free from defects
in materials and workmanship for the period of 90 days from the date of purchase. This warranty
does not apply to damage due directly or indirectly, to misuse, abuse, negligence or accidents,
repairs or alterations outside our facilities, criminal activity, improper installation, normal wear
and tear, or to lack of maintenance. We shall in no event be liable for death, injuries to persons
or property, or for incidental, contingent, special or consequential damages arising from the use
of our product. Some states do not allow the exclusion or limitation of incidental or consequential
damages, so the above limitation of exclusion may not apply to you. THIS WARRANTY IS


To take advantage of this warranty, the product or part must be returned to us with
transportation charges prepaid. Proof of purchase date and an explanation of the complaint must

the product at our election or we may elect to refund the purchase price if we cannot readily and
quickly provide you with a replacement. We will return repaired products at our expense, but if
we determine there is no defect, or that the defect resulted from causes not within the scope of
our warranty, then you must bear the cost of returning the product.

from state to state.
3491 Mission Oaks Blvd. • PO Box 6009 • Camarillo, CA 93011 • [phone]