Another unique take on driven-toolholder design is offered by San Antonio, Fla.-based Exsys Tool Inc., which represents the Eppinger brand. Product Support Manager Scott Leitch said torque transfer is critical with driven tooling. “Our tools use what’s called a compensating clutch. This helps compensate for any misalignment of the turret, and provides more efficient torque transfer from the drivetrain to the part, allowing the toolholder to engage with the bevel gears on the drive mechanism in a much smoother fashion. It also eliminates the noise and vibration that eat up tooling and put a lot of wear and tear on the drivetrain.”

　　The system can also absorb surprises. “If there’s a crash, the clutch is designed to shear away,” Leitch said. “This prevents damage to the machine and can be repaired in a few minutes.”

　　Easy Does It

　　Repair and maintenance should be two key words in the vocabulary of any driven tool user. Glenn Miller, rotary tool repair manager at Minneapolis-based Productivity Inc., provided a number of tips to prolong the life of driven toolholders, starting with the day you take them out of the box.

　　“In terms of life, we don’t see a lot of difference between sealed or unsealed bearings,” he said. “What’s important is how you run the tools in. Some shops get a brand new tool, throw it in the machine and immediately run it wide open. In 9 months, they’re wondering why it’s worn out.”

　　Miller added that even with driven tools that are run-in at the factory, the grease tends to settle to one side of the bearing, leaving the opposite side unprotected. And sometimes there’s too much grease, which creates excessive heat. “On new toolholders or where they’ve been sitting for a long time, run the tool at 1,000 rpm for half an hour, then kick it up to 2,000 or so for another half hour. This spreads the grease evenly throughout the bearing.”

　　In a similar vein, keep an eye on high-pressure coolant. “It sounds silly, but quite often the machinist will change setups and the nozzle ends up pointing at the base of the tool, right where the bearing sits,” Miller said. “In that situation, it doesn’t matter what kind of seal you have—the coolant’s going to penetrate it and wash away the grease.”

　　The good news is that, when properly maintained, driven tools often last upwards of 3 to 4, years barring a crash or improper use. “About 2,000 hours is the magic number for preventive maintenance—no different than any other machine tool,” Miller said. “You spend a couple hundred bucks to send it out for a thorough cleaning, replace the seals, regrease the bearings and you should be good to go.”

　　Despite the power and rigidity of most mill/turn machines, a good dose of common sense is required when using them. “Just because the live tool has a 10-hp motor attached to it doesn’t mean you should expect it to cut like a 10-hp machining center,” said Allen Rupert, director of operations for WTO USA Inc., Charlotte N.C. “The first question you have to ask before purchasing any driven toolholder is what you want to do with it. Can you take a 12,000-rpm toolholder designed for high-speed light machining and use it to cut titanium with a 1 " endmill? Sure, but don’t expect it to last very long. Every one of these tools has a sweet spot, and you need to find the right tool for your application.”

　　Driven tools are fast becoming the new paradigm in machine shops aiming to reduce operations and handling while increasing part quality and profit. CNC machine tool builders continue to offer more capable mill/turn lathes, and toolmakers are rising to the challenge with durable and accurate driven toolholders. However, the successful use of these accessories often comes down to product knowledge, regular maintenance and plain old shop smarts. CTE