Cutting bevel gears on a milling machine represents a practical, albeit less precise, alternative to utilizing dedicated gear generating equipment like bevel gear generators. This method is particularly valuable for prototype development, small batch production, repair work, or educational purposes where dedicated machinery is unavailable or cost-prohibitive. The process relies on a universal dividing head mounted on the milling machine table and a suitable form cutter, typically a single-point tool ground to the desired tooth profile or a standard involute gear cutter approximating the correct form at the large end of the tooth.
(who cutting bevel gears on a milling machine)
The fundamental principle involves indexing the gear blank through precise angular increments using the dividing head while the rotating cutter forms each tooth space sequentially. The critical setup parameter is orienting the gear blank relative to the cutter axis to match the required pitch cone angle. This is achieved by tilting the dividing head spindle to the pitch cone angle. For straight bevel gears, the cutter axis remains perpendicular to the axis of the gear blank. The gear blank must be offset vertically relative to the cutter centerline to ensure the cutter engages the correct portion of the tapered tooth space. Calculating this offset requires knowing the blank diameter, pitch cone angle, and cutter geometry.
The milling operation itself employs a down-cut or up-cut strategy depending on setup rigidity and material. Careful control of depth of cut per pass is essential, especially for harder materials, to prevent tool deflection, chatter, and poor surface finish. Multiple passes are typically required to reach the full tooth depth. Generating the correct tooth profile presents a significant challenge. A standard involute form cutter approximates the correct profile only at the large end of the tooth; the profile becomes progressively less accurate towards the small end due to the inherent taper and curvature of the bevel gear tooth. While acceptable for slower speeds or less critical applications, this profile error limits the achievable smoothness and load capacity compared to gears cut by generation. For higher accuracy demands, a custom-ground single-point form cutter matching the exact desired tooth profile at a specific section is necessary, though more expensive.
Indexing accuracy is paramount. Any error in the dividing head or its setup translates directly into uneven tooth spacing (index error), causing noise and vibration. Rigorous setup verification using dial indicators and meticulous calculation of dividing head settings are crucial. Fixturing the blank securely to withstand cutting forces without deflection is equally important. Coolant application is recommended, especially for ferrous metals, to control heat, extend tool life, and improve surface finish. Continuous monitoring during the cut for signs of chatter, excessive vibration, or tool wear is essential for maintaining quality.
The primary advantage of milling bevel gears lies in accessibility. Utilizing existing milling equipment avoids the need for specialized, expensive gear cutting machines. This flexibility makes it suitable for one-off jobs or low-volume production. However, several inherent limitations must be acknowledged. The process is significantly slower than dedicated gear generation due to the sequential, single-tooth cutting approach and manual indexing. Achieving high levels of profile accuracy and surface finish is difficult and often requires skilled manual intervention and specialized tooling. While straight bevel gears are feasible, cutting spiral bevel gears with their complex curved teeth is generally impractical on a standard milling machine due to the required simultaneous rotational and translational motions during cutting. The process demands a high level of operator skill in setup, calculation, cutter grinding, and machining technique to achieve acceptable results.
(who cutting bevel gears on a milling machine)
In conclusion, milling bevel gears on a conventional milling machine is a viable technique within specific constraints. It offers a practical solution for creating straight bevel gears when dedicated equipment is inaccessible. Success hinges on meticulous setup, precise indexing, appropriate cutter selection, and careful machining practice. While it cannot match the accuracy, speed, or versatility of dedicated bevel gear generators, particularly for spiral bevels or high-precision applications, it remains a valuable skill for the mechanical engineer or machinist tackling prototyping, repair, or small-scale production challenges where flexibility and resource utilization are paramount. Understanding the limitations and managing expectations regarding achievable tolerances and surface finish is critical for successful implementation.