ANTI-KICKBACK DESIGN
Anti-kickback was developed to ensure safety and is considered a standard feature on larger diameter CMT bits where 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 with generous rounded shoulders between the flutes to stay in almost constant contact with the wood when cutting and also to make a smoother initial connection with the work piece.
CMT designed rounded shoulders between the flutes to radically reduce dangerous kickback.
 
 
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 SHEAR ANGLE
Hold a bit by the sank 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.
Our CMT Mortising bit (left) has a negative shear angle of 6 degrees and our Cavetto Edge Mold bit (right) a positive shear angle of 15 degrees.
 
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 HOOK ANGLE
The hook angle is sometimes called the rake ad 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 curved grind on the outer cutting edge of the carbide. The presence of extra mass behind the cutting edge gives the carbide many added advantages:
-strength behind the edge
-stays sharper longer
-gives more resharpening
-prevents burning
-reduces chattering
CMT includes radial relief on all straight edge bits to guarantee durability and the best highest quality performance.
 
 The hook angle is determined by the slant of the cutting edge toward the center of the bit.
 Radical relief grind compared to flat grind.
 CLEARANCE
A major 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 ad it serves as a free space for the bit to avoid coming into contact with the work piece and burning, and as an exit for sawdust.

 

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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