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MATERIAL AND CUTTING SPEEDS
• The ease with which material can be
drilled is dependent on several factors
including tensile strength and abrasion
resistance.
Whilst hardness
strength is the usual criterion, wide
variations in machinability can exist
among material showing similar physical
properties.
• The
cutting
dependent upon requirements for tool
life and surface finish and further
restricted by the rigidity of the tool and
work piece, lubrication, and machine
power available.
• The harder the material the lower
the cutting speed. Some materials of low
hardness contain abrasive constituents
leading to rapid cutting-edge wear at high
speeds. Feed rates are governed by
rigidity of set up, volume of material to be
removed, surface finish and available
machine power.
and/or
conditions
can
• It is preferable to set and maintain a
constant surface speed (RPM) for a given
material and vary the feed rate within
defined limits.
• Machine feed is measured in inches
or millimeters per minute and is the
product of RPM x number of teeth in the
cutter x feed per tooth. Too light or
be
excessively high feed rates will both cause
premature cutter failure. Heavy feeds on
hard materials will cause chipping of the
cutting
edge
generation.
• Slender and long shanked cutters
are restricted in feed rate due to
deflection, and wherever possible the
largest and most robust tool must be used.
This is important for harder materials.
Steel up to 400 HB is the potential limit for
conventional M2 HSS tools.
Above 300 HB, cobalt alloy cutters should
be considered for increased tool life. In
softer grades of material, cobalt alloy
cutters may give increased output by
increasing speeds and feed rates by up to
50%. Tungsten Carbide cutters permit
surface speeds and feed rates up to
those for standard cutters.
and
excessive
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