Adjusting The Speed; Working Advice - Bosch GBM 50-2 Professional Manual Original

26 | English
net switches on automatically as soon as the indicator (16)
on the residual current device (15) lights up red.
Overload protection
The power tool is equipped with an overload protection sys-
tem. In normal conditions of use, the power tool cannot be
overloaded. In the event of overloading, the power tool auto-
matically shuts off the electronics. The magnet will remain
active.
– To start the power tool again after this, press the motor
on/off switch (9) into position "I".
Carry out the following steps before you continue working
with the power tool:
– Eliminate any blockages that may be present. If the ap-
plication tool jams, the anti-clockwise rotation function
must not be used.
– Allow the power tool to run with no load for approx. one
minute; afterwards, it will be ready for use again.
Overload indicator
The overload indicator (6) indicates whether an overload
has occurred when the power tool is switched on.
Green continuous light No overload
Yellow continuous Heavy workload
light
– Reduce feed speed
Red flashing light Very heavy workload
– Reduce feed speed or switch off
motor, otherwise overload pro-
tection will be activated

Adjusting the Speed

Select the correct speed before starting work. The
u
speed must be appropriate for both the drilling dia-
meter and the material you intend to drill. When the
speed is set incorrectly, the application tool can become
damaged or get caught in the workpiece.
Mechanical gear selection
Only operate the gear selector switch (19) when the
u
power tool is not in use.
You can preselect two speed ranges with the gear selector
switch (19).
First gear:
Low speed range for working with large drilling diameters.
Second gear:
High speed range for working with small drilling diameters.
– Press the release button (18) and turn the gear selector
switch (19) into the required position.
– If the gear selector switch is not able to be rotated in
place, turn the application tool slightly and then change to
the required position.
Speed control
You can preselect the required speed using the speed
preselection thumbwheel (2), even during operation.
The required speed depends on the application tool used
and the material being machined. This will prevent the ap-
1 609 92A 4S6 | (10.05.2019)
plication tool from overheating when drilling and guarantee
high drilling quality.
Speed preselection
−1
First gear: 50–255 min
−1
Second gear: 100–510 min

Working Advice

Workpiece Properties
The magnet retention force of the power tool essen-
u
tially depends on the thickness of the workpiece. The
greatest magnet retention force is achieved using soft
steel with a thickness of at least 20 mm.
Note: When drilling into thinner steel, an additional steel
plate (of at least 100 x 200 x 20 mm) must be placed under
the magnetic base. Ensure that the steel plate cannot fall off.
General Advice
Secure the power tool with a safety strap when work-
u
ing overhead or on non-horizontal surfaces. In the
event of a power failure or overload, the magnet retention
force is not maintained. The power tool may fall over and
cause accidents.
If the application tool jams, do not apply any more
u
feed; instead, switch off the tool. Investigate the reason
for the application tool jamming and eliminate the cause.
Do not use the anti-clockwise rotation function.
Always check all parts of the coolant supply system
u
before beginning work. Never use damaged parts.
Keep the coolant away from tool parts and people in
u
the working area.
The surface of the workpiece must be smooth and clean.
Smooth out coarse irregularities, e.g. welding spatter, and
remove loose rust, dirt and grease. The retention force of the
magnet only applies for suitable surfaces.
The motor of the power tool can only be started when the
magnet is switched on. Before drilling, the status of the mag-
net strength (21) should be checked.
Magnet Magnet strength
strength indic-
ator
Green continu- Sufficient magnet strength
ous light
Red flashing Insufficient magnet strength; the power
light tool must not be used.
Causes: Material not thick enough, un-
even surface, coated in paint, scale or
zinc, unsuitable material (e.g. high-car-
bon steel)
– Use a drill emulsion or cutting oil for cooling and lubrica-
tion in order to prevent the drill bit from overheating or
jamming.
Application tool
Annular cutter (dia.
35−50 mm), screw
tap
Twist drill, annular cut-
ter (dia. < 35 mm)
Bosch Power Tools