A big advantage of gang tooling is rapid cycle Arial, aided by fast tool changes for parts that are not typically complex, said Brian Ferguson, product manager of lathes for Hardinge Inc. (Elmira, NY). For these parts, turret tooling can lead to excess cycle time as tools index.

For gang tooling applications, Hard-inge has patented an interchangeable tool top plate with a dovetail bed configuration that provides structural rigidity and clamping of tools during machining operations. The system allows the top plate to be changed in less than 1 minute, with repeatability within 0.0002 inch. Unlike some other top plate systems, all of the tooling does not have to be removed on a Hardinge system to add a tool. Instead, an individual tool can be replaced with another. "It's quick and accurate," said Ferguson.

The top plates for gang tooling can be set with tooling for various jobs and then stored, along with the part program, for future job runs. Another top plate that is tooled up can be put into place, the program uploaded and within minutes, parts are being machined. Some projects may require several different top plates to accommodate a range of part sizes. For example, bar stock that has 1/2 inch diameter may need different tooling than 1-1/8 inch diameter bar stock. If the tooling is determined and set up front, changeover time is decreased.

While gang tooling limits the amount of live tooling offered because of limited space on the cross plate, turret tooling provides the flexibility of making each station a live tooling station.

A turret type machine also can be outfitted with a secondary spindle, or subspindle, which allows for more complex machining jobs. Once machining on the main spindle is complete, then the part can be transferred to the subspindle for work on the back side of the part, resulting in completed parts on a single machine.

"Turret systems give flexibility in productivity," said Chen. "Manufacturers can do what they want, whether the part is short or long."

Disadvantage: cost
While turret systems provide flexibility for more complex jobs, Chen said a disadvantage with turrets is that the tooling costs more than for gang tooling. Turret tooling can be more complex because more tools can be added, and therefore, maintenance time and cost is greater. For example, Chen said, if a turret machine crashes, it will take some time to get it up and running again, but if gang tooling crashes, another tool plate can be put in place. Although it is a rare occurrence, Chen said it is possible for the indexing to malfunction on a turret system.

"Gang-type tooling is nothing more than positioning," said Ferguson. "Once the tools are set on the plate, there's no opportunity for anything to occur when moving from tool to tool other than positioning problems."

How does a manufacturer determine which tooling system is best for its needs? Although some of the same parts can be machined with either type of tooling, both Chen and Ferguson agree that if a part needs an extensive amount of live tooling, then turret tooling is the way to go. "A gang type system is limited in the amount of live tooling holders it can accommodate," said Ferguson. The Hardinge system currently accommodates one, while turrets can hold either 10 or 12 live tools, depending on the size of the turret.

Companies not requiring many tool changes can use gang tooling, said Chen. Gang tooling saves the index time associated with turret tooling, which increases cycle time and adds to the bottom line--more parts per hour and the ability to accept other jobs. "I would try to use a gang tooling machine when running a 1-1/2 inch and smaller diameter part because it is very fast," said Ferguson. "Cycle time is going to be shorter because there is no indexing time." A turret takes longer because it has to go back, raise, index and lock back into place.

Gang tooling systems are limited in the length of workpieces that can be accepted. Turret tooling systems are usually equipped with a tailstock to provide steady support for the back end for turning of longer pieces. Gang systems lack such capability.

Application and part size are the best determinants when choosing the tooling for a turning system.