The large gear in a reduction, typically on the output shaft of a mill, kiln, crane or compressor drive, and often the most expensive part in the box. On a manual lathe the term also names the large spindle gear engaged by the back gear. Big bull gears are often fabricated or cast with a bolted or welded rim, and on open drives they are lubricated by spray.
Heard on the job
Bull gear on the ball mill is fine, it's the pinion that's pitted, so flip the pinion and run the other flank.
Insider tip
Flipping an open-drive pinion end for end puts the unused flank to work and buys time on a worn set.
Also heard as
- girth gear
- main gear