Feature Stories Archive
Routing With Air
Though simple in concept, air
routing is a technologically advanced process that has paid
its dues and is now the choice of many manufacturers.
BY VAN NISER
Pneumatic (or air) routing has been a standard in many
shops and plants for decades; its appeal only seems to
increase as technology advances. Air routers are simple
machines that use high-tech tooling to produce parts that
would be difficult or unsafe to machine in any other manner.
They offer the advantages of light weight, easy-to-maneuver
design, no risk of electrical shock and simple maintenance.
Because of these advantages, air routers are the router of
choice for many industrial hand routing applications.
Air routers are used to cut most machinable materials
used today including, but not limited to: plastics,
fiberglass or fiberglass/wood composites used in the boat
industry and aluminum used in both the boat and aerospace
industries. Their applications include: cut-out routing
through the use of a template; trimming operations while
following a fixture; free-hand trimming; and, as technology
grows, robotic applications.
With the wide variety of materials and applications in
use and only a few variations of the standard air router
available, fabricators must look to specialized tooling to
provide the best solution for their cutting needs.
Tooling Requirements for Air Routers
Router bits for air routers are specialty tools. They
look different, perform better and, as opposed to standard
router bits, are designed specifically for air routers. Air
router tools have the following notable differences:
- Longer Overall Length: Air router tools must extend
out to the collet, through the nose bushing and out of
the guard. For this reason, the tools are typically 31Ú4
in. up to 41Ú2 in. long.
- Undersized Cutting Edge Diameter (CED): Bits must
pass through a support bushing or bearing. Because of
this, the CED is typically toleranced (-0.001/-0.008).
Since hand routing is not normally an operation that
requires high tolerance, this is an accepted method of
protecting the cutting edge from damage due to contact
with the bushing or nose guard.
- Short Flute Fadeout: This adds strength to the tool
by adding material to the place which will have the most
amount of stress. Short fadeouts also allow the bushing
to rest closer to the actual cutting surface.
- Smooth, Large Radius Cam Fadeout: Similar to the
flute fadeout, this adds strength in a weak area of the
tool. The back of the cutting edge usually doesn't see
much action, so this added material has only a minimal
negative effect on the cutting action while decreasing
the instances of breakage.
- Large Chamfer: This prevents damage to the bearings,
bushings and collet.
Air router bits offer the same variety of cutting
geometries as standard bits. Just like standard tools, air
router bits must be selected according to the material being
cut, finish and feed desired, and operator fatigue from hand
routing. Reduced operator fatigue is normally at the expense
of cutting tool life and this must be considered during tool
Some general recommendations for tool selection are as
- Single flute tools are very aggressive. Use them
where high feed rates are needed and finish is a
- Two flute tools are much more stable in the cut,
easier to control and produce a better finish.
- A premium finish can be obtained by taking two
passes: one roughing pass with a single flute tool and a
second finishing pass with a three- or four-edge tool,
removing a thickness of material equal to approximately
1Ú4 the diameter of the bit.
- If a spiral is desired, use a downcut. This ejects
the chips away from the operator and can help hold the
part in place.
- When cutting thin materials, use a straight tool.
This will help stabilize the material.
Operating Conditions and Maintenance
The recurring problem of inconsistent finishes,
inconsistent tool life, or router bit breakage plagues all
users. This is usually blamed on the tool because it is the
item that is most visible and costly in a routing operation.
But there are a multitude of other factors which are much
less visible and more likely to cause the problems listed
Air Pressure: In general, routers need 90 psi and
30 cfm of dry, clean, lubricated air supply. If the router
is receiving less than 70 psi or 20 cfm, then its usable
horsepower is cut in half, as well as exhibiting a drop in
Router bits are designed for specific RPMs and do not
perform well at lower spindle speeds. Air pressure should
not drop more than 10 percent from the static pressure when
the router is turned on. Too many quick disconnects, too
small of a supply line, or too many users on a line can
cause these pressure problems. If air pressure drops while
the spindle is under load, it may be an indicator that the
router itself is in poor repair and may need an overhaul.
Wrong Spindle Speed: Whether the result of low air
pressure, a router in poor condition, or just the wrong
router, spindle speed can greatly affect the performance of
router bits. The smaller the diameter of the tool, the
higher the spindle speed needed to cut at peak performance.
Tools with 1Ú8-inch diameters work extremely well in some of
the older turbine-style routers that spin up to 40,000 rpm.
Coolant: If cutting some plastics or aluminum is a
problem, use coolant. Many manufacturers keep a block of
beeswax or barsoap at each routing station. The operator
dips the bit into the block before each cut, greatly
facilitating chip removal and producing more consistent
Maintenance: As with any machine, maintenance is
critical. Air routers are extremely susceptible to
particulate damage due to their operating environments and
are notorious for not having regular maintenance and
overhaul performed on them. The spindle and nose bearings
(see diagram above) are shielded, but not sealed. They
should be replaced a minimum of every 3-6 months. Vanes for
the spindle should be replaced every six months. Collets
should be replaced every 2-6 months depending on material
being cut and router use.
Spindles are usually concentric to 0.0005 in. from the
factory. Regular use can cause this number to increase up to
0.002 in. A damaged or dirty collet, along with a used nose
bearing, can increase this and cause runout at the tool tip
to exceed 0.010 in. When there is this kind of collaborative
runout -- spindle, spindle bearing, collet and nose bearing
-- the tool can have runout varying from zero to 0.010 in.
each time it is seated and tightened down. What this
translates to is when an operator is doing a repetitive
operation, he will see one tool perform extremely well and
get a maximum number of parts, while the next tool will be
difficult to push, give a poor finished surface and cut
drastically fewer parts. The bit is always blamed but is
rarely the actual problem.
Operator training: Air routing, without a doubt,
is very "feel" oriented. An experienced operator can tell
when a bit is dull or when performance of the tool and bit
drop. New operators will always break more tools than an
experienced counterpart. It just takes one hit of the tool
on the fixture, one time when a single edge tool gets away
from the operator, or one plunge too fast or erratic and the
cutting edge will chip. This chip will immediately degrade
performance and cause the tool to behave differently. This
starts a chain reaction and the entire cutting edge is
corrupted in a short time. When evaluating router and router
bit performance, do not forget operator competency.
Air routing has been around for a long time and will
continue to be an extremely viable method for trimming
and/or manufacturing parts. With the correct tooling and an
excellent maintenance program, air routers are more reliable
and comfortable to use than electric routers in abusive or
repetitive applications and can be a cost effective
alternative to CNC machines.
Van Niser is director of Plastic Application
Engineering at Onsrud Cutter. Based in Libertyville, IL,
Onsrud Cutter is a manufacturer of a wide range of cutting
tools for the plastics industry.
Plastics Machining & Fabricating
F: (847) 362-5028