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15
14.7 Teeth shape
“C” TYPE SHARPENING (HZ)
Coarse toothing with roughing tooth raked on both
sides and non-raked finishing tooth. The roughing
tooth is about 0.3 mm higher.
Coarse toothing with roughing tooth and finishing
tooth. Used in saws with pitch greater than or equal
to 5 mm for cutting ferrous and non-ferrous
materials with solid or solid-profiled
sections.
Figure 15
“BW” TYPE SHARPENING DIN 1838--UNI 4014
Coarse toothing with teeth alternately raked to the
right and left.
Toothing generally used on cut-off machines for
cutting ferrous and alloy materials with tubular and
profiled sections.
Figure 16
POSITIVE AND NEGATIVE CUTTING ANGLES
The cutting angle may vary from positive to
negative depending on the cutting speed, the
profile and the type of material to be cut.
A positive angle determines better penetration of
the tool and hence lower shear stress and greater
ease of sliding for the swarf over the cutting edge.
On the other hand, the cutting edge has lower
mechanical resistance, so that as the breaking load
of the material to be cut increases, the cutting
angle decreases from positive until it becomes
negative, thus offering a cutting edge with a larger
resistant section.
Figure 17
Short swarf material such as brass, bronze,
aluminum and hard cast iron require smaller cutting
angles because the swarf becomes crushed
immediately and the rake angle has little effect
during the cutting stage.
The cold saws use discs with positive cutting
angles for cutting solid materials and with negative
cutting angles for cutting hollow profiles. This is
because, as a result of the high cutting speeds,
even with non-ferrous materials the tool ”strikes”
against the wall of the profile to be cut several
times, thus requiring a cutting edge with a larger
resistant section.
Figure 18
Circular saws can also be characterized by other
parameters such as the whine reduction feature,
which cuts down noise at high speeds, or
expansion, which compensates for the pushing of
chips inside the cutting edge, thus reducing the
thrust on the walls of the material to be cut.
Figure 19