How
We Produce Our High Quality Bits
RESEARCH, GEOMETRY AND
DESIGN
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ANTI-KICKBACK DESIGN
Anti-Kickback was developed to
ensure safety and is considered a standard feature on larger diameter CMT bits
where the risk of kickback is the highest. Kickback occurs when the bit makes
the initial bite into the wood and jumps back. Due to the large amount of space
between the flutes on the cutter head. CMT bits are designed to stay in almost
constant contact with the wood when cutting and also to make a smoother initial
connection with the workpiece.
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CMT designed
rounded shoulders between the flutes
to radically reduce dangerous kickback.
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SHEAR ANGLE
Hold a bit by
the shank and look at the cutting edge,
you will notice that it goes either straight up and down, left to right
(negative shear) or right to left (positive
shear). The angle cutting edge or its "shear" will determine how the
cut is made. Specific shear angles are
designed to work best in certain type
of materials. A shear angle gives a less
choppy cut and give a cleaner finish,
thus making them preferred over straight
cutting edges for edge work. Negative
shear cutting angles give the smoothest
finish and are recommended for laminate
work. |
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Our CMT Mortising
bit (left) has a negative shear angle
of 6º
and our Cavetto Edge Mold (right) a positive shear angle of 15º.
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HOOK ANGLE
The hook angle
is sometimes called the rake and you
can see it by looking down at the top of your bit – notice the angle
the cutting edge makes with the overall bit diameter. (See drawing) This
is the angle at which the cutting edge meets the
stock and its purpose is to help leave
a smoother, splinter-free finish.
RADIAL RELIEF
Radial relief is the curve grind on the
outer cutting edge of the carbide. The presence of extra mass behind the
cutting edge gives the carbide many added advantages:
- more strength
behind the edge
- stays sharper
longer
- gives more
resharpenings
- prevents
burning
- reduces
chattering
CMT included
radial relief on all straight edge bits to guarantee durability and the best
high quality performance. |
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The hook angle is determined by
the slant of the cutting edge towards
the center of the bit.
Radial relief grind compared to
flat grind.
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CLEARANCE
A minor feature
that makes a major difference in tool performance is clearance space. As the
bit rotates, the tip of the cutting edge makes an outer circle as it removes
stock, and the rotation of the body makes a smaller inner circle. The little
space created between the rotation of the tip and the rotation of the body (See
photos right) is known as the clearance and it serves as a free space for the
bit to avoid coming into contact with the workpiece and burning, and as an exit
for sawdust. |
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Notice the space created when measuring
the diameter from the cutting edge (left) and from the body of the
bit (right).
This little space makes a big difference
in the efficiency of chip and sawdust ejection.
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PUTTING IT
TOGETHER
TURNING
Bar stock steel is turned on a CNC lathe into the
recognizable first shape of the router bit (See photos 1 and 2). Bits are
centered and balanced, making the holes visible on the top and bottom of every
bit that are followed in every step of production to ensure concentric
machining. Notice the very smooth finish on a turned CMT bit. Even though it
will be removed and refinished during later phases, we feel that starting with
precision and paying attention to details means a better end product.
MILLING
After turning, the bits are milled to
make the flutes and seats for the carbide tips and putting a finer finish on
the bit body and shank (See photo 3). Looking at the flutes of a bit at this
stage, you can see the shear angle of the bit. Milling is done on Swiss
automatic and automated loading CNC machines for a perfectly smooth and
accurate finish, especially the seats where the carbide tips will be brazed.
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