Routing with Air
Pneumatic (or air) routing
has been a standard in many shops and plants for decades and 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 a 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 routable materials used today including, but not limited to: fiberglass
or fiberglass/wood composites in the boat industry, aluminum in both the boat
and aerospace industry, and plastics in a wide variety of production 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, manufacturers
must look to specialized tooling to provide the best solution to their cutting
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 Lengths
- Air router tools must extend out of the collet, through the nose bushing,
and out of the guard. For this reason the tools are typically 3-1/4" up
to 4-1/2" long.
- Undersized Cutting
Edge Diameter (CED) - Bits must pass through a support bushing or bearing.
For this reason the CED is typically toleranced (-.001/-.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
(see diagram - B) - This add strength to the tool by adding material where
the most amount of stress is. Short fadeouts also allow the bushing to rest
closer to the actual cutting surface.
- Smooth, Large Radius
Cam Fadeout (see diagram - C) - Similar to the flute fadeout, this adds
strength in a weak area of the tool. The back of the cutting edge usually does
see much cutting action so this added material has only a minimal negative effect
of the cutting action while decreasing the instances of breakage.
- Large Chamfer (see
diagram - A) - 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. Operator fatigue is a variable not normally
associated with bit selection in the current climate of diminishing hand routing
operations in favor of CNC production. Reduced operator fatigue is normally
at the expense of cutting tool life and this must be considered during tool
selection. Some general recommendations for tool selection are as follows:
- Single flute tools are
very aggressive. Use them where high feed rates are needed and finish is a secondary
- Two flute tools are much
more stable in the cut, are 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 ¼ 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.
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. There are a multitude of other
factors that are much less visible and more likely to cause the problems listed
- Air Pressure -
In general, routers need 90psi and 30cfm of dry, clean, lubricated air supply.
If the router is receiving less than 70psi or 20cfm, then its usable horsepower
is cut in half as well exhibiting a drop in its RPMs. Router bits are designed
for specific RPMs and do not perform well at lower spindle speeds. Air pressure
should not drop more than 10% 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 tool, the higher the spindle speed needed to
cut at peak performance. 1/8" diameter tools work extremely well in some
of the older turbine style routers that spin up to 40,000RPM.
- Coolant - If cutting
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 and it greatly facilitates chip removal and produces 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) are shielded but not sealed. They should be
replaced a minimum of every 3-6 months. Vanes for the spindle should be replaced
every 6 months. Collets should be replaced every 2-6 months depending on material
being cut and router use.
Spindles are usually concentric
to .0005" from the factory. Regular use can cause this number to increase
up to .002". A damaged or dirty collet along with a used nose bearing can
increase this and cause runout at the tool tip to exceed .010". When there
is this kind of collaborative runout (spindle, spindle bearing, collet, and
nose bearing) the tool can have runout varying from zero to .010" each
time it is seated and tightened down. What this translates to is when an operator
is doing a repetitive operation, they 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 - 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 to 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