Flycutters in Machining: Applications on Lathes and Milling Machines

Flycutters are versatile cutting tools that serve important but distinctly different functions when used on lathes versus milling machines. This article explores how these simple yet effective tools operate in both environments, their advantages, and best practices for their use.

Flycutters on Milling Machines

On a milling machine, a flycutter is a single-point cutting tool that rotates in a circular path to create a flat surface. Unlike traditional face mills that have multiple cutting edges, the flycutter typically has just one cutting bit mounted on an arm that extends from a central shaft.

Function and Operation

When mounted in a milling machine spindle, the flycutter rotates to remove material in a sweeping motion. The single cutting edge takes a shallow cut with each revolution, gradually creating a flat surface across the workpiece. The simplicity of this design allows for:

• Creating wide, flat surfaces with a single pass
• Achieving excellent surface finishes due to the intermittent cutting action
• Working with relatively low horsepower requirements
• Cutting larger areas than would be possible with standard end mills

Advantages

Flycutters excel at facing operations on milling machines. Their large cutting diameter allows machinists to surface wide areas efficiently. The interrupted cutting action also helps dissipate heat, reducing the risk of warping both the tool and workpiece. Additionally, flycutters are often less expensive than comparable diameter face mills and can be easily resharpened or fitted with replaceable inserts.

Applications

On milling machines, flycutters are primarily used for:

• Facing operations on large flat surfaces
• Creating precise datum surfaces
• Cleaning up rough castings
• Precision leveling of workpieces
• Creating decorative finishes with distinctive circular patterns

Flycutters on Lathes

When used on a lathe, a flycutter functions quite differently. On a lathe, it's typically mounted on the tool post or in the tailstock and serves as a specialized boring or facing tool.

Function and Operation

In lathe applications, the flycutter remains stationary while the workpiece rotates. The cutting action occurs as the rotating workpiece makes contact with the stationary cutting edge of the flycutter. This arrangement is essentially the reverse of how a flycutter operates on a milling machine.

Applications on Lathes

On lathes, flycutters are primarily used for:

• Boring large diameter holes
• Facing operations, particularly on the internal surfaces of hollow components
• Creating precise internal shoulders or recesses
• Machining large diameter features without specialized tooling

Advantages

The primary advantage of using a flycutter on a lathe is the ability to machine large internal diameters without specialized tooling. This makes flycutters particularly valuable for one-off jobs or shops with limited tooling budgets. Flycutters can reach areas that might be difficult to access with standard boring bars, allowing for more versatile internal machining operations.

Key Differences in Application

The fundamental difference between using flycutters on lathes versus milling machines is in the movement of the tool and workpiece:

• On milling machines: The flycutter rotates while the workpiece remains stationary (except for feed motion)
• On lathes: The workpiece rotates while the flycutter remains stationary (except for feed motion)

This difference leads to variations in cutting forces, chip formation, and appropriate speeds and feeds. On milling machines, the flycutter experiences intermittent cutting, taking a chip only during a small portion of each revolution. On lathes, the cutting action is continuous as long as the tool is engaged with the rotating workpiece.

Safety Considerations

Flycutters require careful attention to safety, especially on milling machines where they rotate at high speeds with an extended cutting arm:

• Always use appropriate guards and shields
• Set reasonable spindle speeds to prevent excessive centrifugal forces
• Ensure proper tool balance to minimize vibration
• Secure workpieces properly to prevent movement during cutting
• Use cutting fluids as appropriate to manage heat and improve finish

Conclusion

While sharing the same name, flycutters perform distinctly different operations on lathes versus milling machines. Understanding these differences allows machinists to leverage these versatile tools appropriately for their intended applications. Whether facing a large surface on a mill or boring an internal diameter on a lathe, the flycutter remains a valuable and cost-effective tool in the machinist's arsenal.