A rotary broach, also known as a wobble broach, is a precision tool used in machining to create polygonal shapes such as hexagons, squares, or other custom profiles inside a pre-drilled hole. It is commonly used in CNC lathes, mills, and other machining centers to produce internal features in components like fasteners, gears, and medical devices. The rotary broaching process involves a broach tool that is slightly tilted, typically at a 1-degree angle, relative to the workpiece. This tilt allows the broach to "wobble" as it rotates, enabling it to cut the desired shape into the material. The broach is mounted in a special holder that allows it to rotate freely. As the workpiece rotates, the broach is fed into the hole, and the cutting edges of the broach progressively remove material to form the desired profile. The key to the rotary broaching process is the combination of the tool's rotation and the wobbling motion, which reduces the cutting forces and allows for efficient material removal. This method is advantageous because it can produce precise, clean, and burr-free internal shapes in a single pass, without the need for secondary operations. Rotary broaching is highly efficient and can be used on a variety of materials, including metals and plastics. It is particularly beneficial for producing small to medium-sized features with high accuracy and repeatability. The process is also relatively fast, making it suitable for high-volume production environments.

Rotary broaching is a versatile machining process used to create polygonal shapes in a variety of materials. The materials that can be broached using a rotary broach include: 1. **Metals:** - **Steel:** Both carbon and alloy steels, including stainless steel, can be broached. The hardness of the steel will affect the tool life and the broaching speed. - **Aluminum:** Due to its softness and machinability, aluminum is commonly broached, allowing for quick and efficient operations. - **Brass and Copper:** These materials are easily broached due to their ductility and low hardness. - **Titanium:** Although more challenging due to its strength and toughness, titanium can be broached with appropriate tool design and cutting parameters. - **Inconel and Other Superalloys:** These high-strength materials can be broached, but they require specialized tooling and careful process control. 2. **Non-Metals:** - **Plastics:** Many types of plastics, including thermoplastics and thermosetting plastics, can be broached. The process is particularly useful for creating precise internal shapes in plastic components. - **Composites:** Certain composite materials can be broached, though the process may require adjustments to account for the material's layered structure and potential for delamination. 3. **Other Materials:** - **Wood:** Although less common, wood can be broached, especially in applications requiring precise internal shapes. - **Ceramics:** Some ceramics can be broached, but the process is challenging due to the material's brittleness and hardness. The choice of material affects the broaching process, including tool design, cutting speed, and lubrication. Proper selection of these parameters is crucial to achieving the desired results and prolonging tool life.

1. **Select the Broach and Holder**: Choose the appropriate rotary broach and holder for your application. Ensure the broach is sharp and the holder is compatible with your machine. 2. **Install the Holder**: Secure the rotary broach holder in the lathe tailstock or milling machine spindle. Ensure it is tightly fastened to prevent movement during operation. 3. **Align the Holder**: Align the holder with the workpiece. In a lathe, ensure the holder is centered with the spindle axis. In a milling machine, align it with the spindle centerline. 4. **Set the Tool Length**: Adjust the tool length so that the broach protrudes slightly beyond the holder. This ensures proper engagement with the workpiece. 5. **Secure the Workpiece**: Clamp the workpiece securely in the lathe chuck or milling machine vise. Ensure it is stable and aligned with the broach. 6. **Adjust the Machine Speed**: Set the machine to a low RPM. Rotary broaching typically requires slower speeds to ensure precision and prevent tool damage. 7. **Feed the Broach**: In a lathe, use the tailstock to feed the broach into the rotating workpiece. In a milling machine, lower the spindle to engage the broach with the stationary workpiece. 8. **Monitor the Process**: Observe the broaching process closely. Ensure the broach is cutting smoothly and adjust the feed rate if necessary. 9. **Complete the Broaching**: Continue feeding until the desired depth is achieved. Retract the broach carefully to avoid damaging the workpiece or tool. 10. **Inspect the Workpiece**: After broaching, inspect the workpiece for accuracy and finish. Make any necessary adjustments for future operations. 11. **Clean and Store Tools**: Clean the broach and holder after use. Store them properly to maintain their condition for future use.

Rotary broaching offers several advantages over traditional broaching methods: 1. **Versatility**: Rotary broaching can be used on various machines, including CNC lathes, mills, and manual machines, allowing for greater flexibility in manufacturing processes. 2. **Speed**: The process is faster as it can create complex shapes in a single pass, reducing cycle times compared to traditional broaching, which often requires multiple passes. 3. **Setup Time**: Rotary broaching requires less setup time. The tool is easy to install and align, minimizing downtime and increasing productivity. 4. **Complex Shapes**: It can produce intricate and non-standard shapes, such as hexagons, squares, and splines, with high precision and consistency. 5. **Material Versatility**: Suitable for a wide range of materials, including metals and plastics, without significant wear on the tool, enhancing tool life and reducing costs. 6. **Surface Finish**: Provides excellent surface finish and dimensional accuracy, often eliminating the need for secondary finishing operations. 7. **Tool Life**: The design of rotary broaches allows for even distribution of cutting forces, which extends tool life and reduces the frequency of tool changes. 8. **Reduced Force**: The cutting action requires less force, which minimizes stress on the machine and workpiece, reducing the risk of damage and increasing the longevity of equipment. 9. **Compact Design**: The compact nature of rotary broaching tools makes them suitable for use in tight spaces and on small workpieces. 10. **Cost-Effectiveness**: Lower operational costs due to reduced tool wear, faster cycle times, and minimal setup requirements make rotary broaching a cost-effective solution for many applications.

To maintain and sharpen a rotary broach, follow these steps: 1. **Inspection**: Regularly inspect the broach for wear, damage, or dullness. Look for signs of chipping or uneven wear on the cutting edges. 2. **Cleaning**: Keep the broach clean by removing chips and debris after each use. Use a soft brush or compressed air to clean the tool, ensuring no residue is left that could affect performance. 3. **Lubrication**: Apply a light coat of rust-preventive oil to the broach after cleaning to protect it from corrosion. Ensure the broach holder and spindle are also lubricated to facilitate smooth operation. 4. **Sharpening**: When the broach becomes dull, it needs sharpening. Use a precision grinding machine to sharpen the cutting edges. Ensure the grinding wheel is appropriate for the broach material, typically a diamond or CBN wheel for carbide broaches. 5. **Angle Maintenance**: Maintain the original cutting angles during sharpening. Use a toolmaker’s microscope or a comparator to verify angles and ensure precision. 6. **Balancing**: After sharpening, check the broach for balance. An imbalanced broach can cause poor performance and damage to the workpiece or machine. 7. **Storage**: Store the broach in a protective case or holder to prevent damage. Keep it in a dry, temperature-controlled environment to avoid rust and deformation. 8. **Replacement**: If the broach is excessively worn or damaged beyond repair, replace it to ensure optimal performance and avoid damage to the workpiece or machine. By following these steps, you can maintain the efficiency and longevity of a rotary broach, ensuring precise and clean cuts in your machining operations.