What are typical machine constants for hobbing machines and what are they for?
All hobbing machines use an Index Constant that synchronizes rotation of the workpiece with the cutter. For example, a 30:1 index constant means that the index change gear ratio is equal to 30/Teeth for a single start cutter cutting a spur gear. With the correct index change gears, a single start cutter will rotate a number of revolutions equal to the teeth on the workpiece while the workpiece makes one complete revolution. Index change gears for a differential machine are the same for cutting both spur and helical gears. Some hobbing machines use a dial controlled hydraulic table feed. Other machines use gearing to advance the cutter table. Machines that use feed gearing have a Feed Constant. Machines that have a feed constant will often display it on the machine somewhere as a number (e.g. 8 or 12). CPC-HOB requires dividing this number into 1.0 to get the feed constant. Machines equipped with a differential use a differential formula* to determine differential (or lead) change gears
