Bosch Professional GBM 50-2 Original Instructions Manual page 16

16 | English
– 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-
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
tool must not be used.
light
1 609 92A 4S9 | (10.05.2019)
Magnet
strength indic-
ator
– Use a drill emulsion or cutting oil for cooling and lubrica-
tion in order to prevent the drill bit from overheating or
jamming.
– Metal workpieces should be centre-punched before being
Application tool
drilled.
Annular cutter (dia.
– Twist drill: For drilling diameters > 10 mm, pre-drill with a
35−50 mm), screw
small drilling diameter. This allows you to reduce the con-
tap
tact pressure and puts less strain on the power tool.
Twist drill, annular cut-
– When drilling into metal, only use sharpened annular cut-
ter (dia. < 35 mm)
ters (brand accessories) that are in perfect condition.
– Turn the crank handle (4) to move the drill forwards.
– Select the speed that is appropriate to the specifications
of the tool
Note: When thread-cutting, the lowest speed setting
must be used.
Working with the Annular Cutter
– Only use annular cutters that are free of defects; ensure
that these are in perfect condition before each use. Do
not use any annular cutters that are damaged.
– Switch the power tool off immediately if the annular cut-
ter gets stuck.
– Protect the annular cutter. The tip of the annular cutter is
hard yet fragile.
The following measures will help to slow down the wear and
prevent breakage of annular cutters:
– When drilling in steel, ensure that there is enough coolant
available; use coolant for metal cutting.
– Make sure that the workpiece is level and clean to guaran-
tee the required magnet strength.
– Before drilling, ensure that all parts are properly at-
tached.
– At the start and end of the drilling procedure, the contact
pressure should be reduced by a third.
– If large quantities of metal chips accrue when drilling in
materials such as cast iron, copper die casting, etc., com-
pressed air can be used instead of coolant to assist in the
removal of metal chips.
Neutral Position of the Rotational Direction Switch
The power tool stops if the rotational direction switch (8) is
activated during drilling.
If the rotational direction switch is in the centre position, the
application tool can be rotated clockwise while the on/off
switch for the motor (9) is continuously pressed.
In this way, the thread-cutting process can be ended
smoothly.
Drilling
– Align the power tool by referring to the laser cross on the
workpiece.
Magnet strength
Causes: Material not thick enough, un-
even surface, coated in paint, scale or
zinc, unsuitable material (e.g. high-car-
bon steel)
Bosch Power Tools