CNC gear hobbing, crown hobbing, is a unique lead modification technology that we apply to high-speed spur and helical pinions. This process produces a barrel or “crowned” shape on the flank of the gear tooth to help compensate for misalignment and noise reduction. Forest City Gear helped introduce this technique to the small motor and power tool industries in the US.
Carbide re-hobbing is often used as a more economical approach than gear grinding. It is a post heat-treat gear-finishing process that uses a neutral rake carbide hob to re-cut hardened gears, which helps us achieve a gear quality of AGMA 9 or better. Gears that have been distorted, damaged, or enlarged during heat treatment can be salvaged by this process. Motor armature shafts that have been hobbed with a small diameter hob are the typical candidates for this technique as form grinding each tooth is too slow and small diameter CBN wheels are very expensive.
We also do diagonal hobbing, where we move across the cutting tool to get more cutting surfaces engaged. This helps create a better finish and a more accurate tooth profile on the gear.
During the hobbing process, we continuously shift the hob cutter to an unused part after each part is cut. By frequently moving the cutter during the run of a production lot, we minimize the wear on the cutter, which in turn, reduces the noise on the gear because a more consistent involute is achieved.
On our plant floor, we use a variety of gear hobbers: