Routing with Air
Pneumatic, or air, routing has remained a standard in many production environments because air routers are lightweight, maneuverable, relatively simple to maintain, and well suited to repetitive industrial hand-routing applications.
Air routers are used to machine fiberglass and fiberglass-wood composites, aluminum, plastics, and other routable materials.
Typical applications include template cutouts, fixture-guided trimming, free-hand trimming, and increasingly, robotic operations.
Because the basic air-router design varies relatively little across such a broad range of applications, specialized tooling plays a major role in achieving the desired cutting performance.
Tooling Requirements for Air Routers
Router bits designed for air routers differ from standard router tooling in several important ways.
Longer Overall Length
Air-router tools must extend from the collet, through the nose bushing, and beyond the guard before reaching the workpiece.
Undersized Cutting Diameter
The cutter must pass through a support bushing or bearing. For this reason, the cutting-edge diameter is typically manufactured slightly undersize.
A typical tolerance is approximately -0.001 to -0.008 inch. Since hand routing usually does not require the same dimensional tolerances as precision CNC machining, this allows the cutter to pass through the support system without damaging the cutting edge.
Short Flute Fadeout
A short flute fadeout adds material in an area of high stress, improving cutter strength. It also allows the support bushing to remain closer to the cutting area.
Smooth Cam Fadeout
A smooth, large-radius cam fadeout also strengthens a normally weak area of the tool.
Because the back of the cutting edge performs relatively little cutting, the additional material has minimal effect on cutting performance while helping reduce breakage.
Large Chamfer
A larger chamfer helps prevent damage to the bearings, bushings, and collet as the tool is installed and used.
Selecting Air Router Tool Geometry
Air-router tooling is available with many of the same cutting geometries as standard router bits.
Selection should account for the material being cut, desired finish, required feed rate, and operator fatigue.
Operator fatigue is particularly important in hand routing because aggressive tooling can increase the physical effort required to control the router.
- Single-flute tools: Aggressive cutters suited to high feed rates where finish is a secondary concern.
- Two-flute tools: More stable and easier to control, generally producing a better finish.
- Premium finishing: Use a single-flute tool for roughing followed by a three- or four-edge finishing tool.
- Spiral tooling: Downcut spirals direct chips away from the operator and can help hold the workpiece down.
- Thin materials: Straight-flute tooling can help stabilize the material during cutting.
Operating Conditions and Maintenance
Inconsistent finish, poor tool life, and router-bit breakage are often blamed on the cutting tool itself.
In many cases, however, the underlying cause is air supply, spindle speed, machine condition, collet condition, or operator technique.
Air Pressure
Air routers require sufficient clean, dry, lubricated air to maintain spindle speed and usable horsepower.
If supply falls below roughly 70 PSI or 20 CFM, available horsepower can drop significantly along with spindle RPM.
Router bits are designed around specific spindle-speed ranges and can perform poorly when the router is unable to maintain speed under load.
Air pressure should generally not drop more than about 10 percent from static pressure when the router is switched on.
Excessive quick-disconnect fittings, undersized supply lines, or too many users on one air line can all contribute to pressure loss.
Spindle Speed
Incorrect spindle speed can significantly affect cutting performance.
Smaller-diameter cutters generally require higher spindle speeds. For example, 1/8-inch tools can perform well in high-speed turbine routers operating near 40,000 RPM.
Coolant for Aluminum
When routing aluminum, lubrication can improve chip evacuation and finished-part consistency.
Some shops use beeswax or bar soap at the routing station, dipping the cutter into the material before cutting to provide simple lubrication.
Maintenance Intervals
Air routers operate in environments where dust and chips can accelerate wear, making regular maintenance especially important.
- Spindle and nose bearings: inspect regularly and consider replacement approximately every 3–6 months.
- Spindle vanes: consider replacement approximately every 6 months.
- Collets: replacement intervals may range from approximately 2–6 months depending on router use and material.
Runout and Concentricity
New spindles may leave the factory with concentricity near 0.0005 inch. Regular use can increase this figure to approximately 0.002 inch.
A worn or dirty collet combined with a used nose bearing can increase total runout at the cutter tip substantially.
This can make one cutter appear to perform perfectly while the next is difficult to push, produces a poor finish, or has dramatically shorter life.
In these situations, the bit is often blamed even though the actual cause is the routing system.
Operator Technique
Air routing is highly dependent on operator feel and experience.
An experienced operator can often recognize when a tool is becoming dull or when machine performance begins to change.
A collision with the fixture, loss of control with an aggressive single-edge cutter, or an excessively fast or unstable plunge can chip the cutting edge.
Once damaged, the cutting edge can quickly deteriorate further and produce increasingly poor performance.
Conclusion
Air routing remains a practical method for trimming and manufacturing parts across a wide range of industrial applications.
With correctly designed air-router tooling and a strong maintenance program, pneumatic routers can provide reliable performance in repetitive or demanding hand-routing environments.
For suitable applications, they can also provide a cost-effective alternative to CNC equipment.