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END-MILL GEOMETRIES
angles and depths, depending upon your
desired depth and width of cut.
Engraving
Engraving tools make a shallow cut along a
toolpath. They are capable of etching very fine,
often decorative, details into a surface.
FLUTE TYPES
End mills for machining wood have radial or
helical flutes. Radial flutes are straight grooves
that are parallel to the tool’s axis, while helical
flutes wrap around the tool.
Higher helix angles clear chips away from the
cutting edge faster. Straight tooling with radial
flutes have a 0° helix angle, while spirals for
cutting wood can have a helix angle of up to 35°.
In addition to high helix angles, router bits also
have steeper rake (tool attack angle) and clear-
ance angles to evacuate the chips much faster
than a traditional end mill.
As the tool turns, the direction of the spiral
determines which way chips are ejected. The
two basic types of helical end mills are upcut
and downcut, shown in Figure 6-7.
Stay away from left-hand rotation tools, often
indicated with an “L” or “LH” in the tool num-
ber. They are meant for spindles that rotate
counterclockwise.
Upcut Spiral
This tool’s flutes eject chips upward, out of the
gap created between the cut piece and the
waste material (kerf). Because the chips are
forced up, the material’s top surface can
become chipped or frayed (known as tearout),
while the bottom face will be cleanly cut.
Although upcut tools are very efficient at dissi-
pating heat and clearing chips, they have some
undesirable effects that can make them a poor
choice for routing plywood. The upward chip
movement pulls the material up from the cut-
ting bed, creating a troublesome lifting effect
on lighter, thinner materials. This movement
can also pull at small cut parts and long skinny
parts. This can be problematic for vacuum hol-
downs, and you’ll need to use tabs to keep
parts in place.
Downcut Spiral
A downcut spiral’s flutes push chips downward,
toward the machine bed. When cutting with ¼″
FIGURE 6-7
An upcut tool pushes
chips up and out, while
a downcut tool forces
them down into the
kerf, as it cuts
06/MACHINING FOR DESIGNERS
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