40 | MARCH 2016 www.canadianmetalworking.com
BY BRIAN MACNEIL
With decades of engineering advances in material strength
and designs, engineers are now more
able than ever to push the envelope
when it comes to weight savings in
all forms of transportation, including construction vehicles.
While new techniques offer sound
environmental and cost advantages,
they often present new challenges
Incorrectly applying a cutting
tool to thin, deep, and lightweight
structural sections in a component
often induces the kind of heavy chatter that results in damaged tools,
components, and machine spindles.
Taking advantage of some simple
programming and tool tips can go a
long way in preventing these issues.
Thin walls are described by their
ratio of wall thickness to height.
This ratio changes the cutting technique that must be chosen.
For ratios of less than 30-to-1, use
the step support milling technique.
This provides overlapping support
on opposite sides of the wall. When
you alternate the depth of cut from
side to side, material is left to sup-
port part of the wall for the opposite
side (see Figure 1).
At ratios above 30-to-1, employ
what often is called a Christmas tree
routine. The goal is for the thicker
section below to support the thinner
sections above. The key is to move
down the wall in a stepwise manner,
leaving a greater thickness as you
move down (see Figure 2).
Finishing in either of these scenarios also requires a change in the
usual way of thinking. Conventional
and climb milling give two very
different results based on the chip
formation each causes.
Climb milling tends to have a
pulling effect, while conventional
milling gives more of a pushing
action. Because of this pushing
action, choose conventional toolpaths on thins walls. There is less
deflection, and better accuracy is
maintained, but the possibility of
smearing is increased, so coolant is
recommended in all materials.
In practical terms, conventional
milling has a tendency to cut under-
size, while climb milling tends to
cut oversize, so take this into consid-
eration for setting tolerances.
CUTTING ON THE FLOOR
Thin floors also are typically stated
as a ratio. When the floor becomes
less than 1-to- 30 of the pocket’s
width or length, it is considered
thin. To overcome this, try leaving
more material for a finish pass.
Leaving as much as 4 mm will keep
the base as stable as possible in the
Tool selection is critical. The
higher the helix on the tool, the
more pull it tends to create. This, of
course, has a negative effect on the
Use indexable milling tools whenever possible because they usually
have lower axial cutting forces when
compared to solid-carbide tools.
If solid-carbide tools are the only
option, use one with a low helix
angle and the largest possible
corner radius. The radius has an
opposite effect, creating a chance for
(see Figure 3).
Brian MacNeil is milling products
and application specialist, Sandvik
Coromant Canada, 905-826-8900,
MACHINING THIN WALLS AND FLOORS
Proper technique, coolant use are keys to successful milling operation