Hydro power: Drilling Performance

Courtesy of Matthew Panosh/Schunk

A Schunk CAT40 TENDO Platinum hydraulic toolholder used in a finish milling application.

While hydraulic toolholders have been around for many years, there’s still a good deal of debate about their utility. Advocates extol the extremely tight TIR, crushingly high gripping force and simple operation of hydraulic holders, while detractors say they are expensive and limited to certain applications. The detractors instead tout the versatility and dependability of other toolholding methods. Ultimately, it’s up to the individual machine shop to decide if they are an effective choice.

To Have and to Hold

“Hydraulic toolholding technology … really took a strong hold, especially in the automotive industry, around the turn of the 1980s,” said Alan Miller, engineering manager at BIG Kaiser Precision Tooling Inc., a Hoffman Estates, Ill.-based manufacturer of tooling and toolholders. Compared to collet chucks, with their array of parts, he noted, hydraulic holders are easier to change and provide consistent runout. “People realized that, for large production runs, they were the way to go.”

In contrast to mechanical chucks, hydraulic toolholders are simple to set up: The operator just inserts the tool and turns the actuation screw. That screw causes a piston to push hydraulic fluid into the bladder surrounding the tool shank, compressing the thin metal wall evenly around either the sleeve or directly around the tool shank, providing gripping forces of up to 900 newtons.

According to Matthew Panosh, tooling group manager at Schunk Inc., Morrisville, N.C., Schunk hydraulic toolholders offer runout of 3µm or less measured at 2½ times the clamping diameter. “The real benefit of hydraulic toolholders is that they clamp the tool concentrically,” he said. “You drop the tool in and turn the actuation screw to the dead stop. If you do that 10 times or 100 times, as long as the holder is in good shape, the runout value will be the same.”

In addition to repeatability, hydraulic toolholders are repairable when individual components begin to wear or break. Schunk has repaired and replaced seals in holders up to 15 years old and returned them to full functionality, according to Panosh.

Origin Story

The origins of hydraulic toolholders date to the middle of the last century, according to Bob Andre, vice president of manufacturing at Hydra-Lock Corp., Mt. Clemens, Mich. “Hydraulically actuated part and tool holding first came on the market in 1947, with Hydra-Lock being an originator of much of the technology,” Andre said, adding that Hydra-Lock patented some of that technology.

However, the role of hydraulic toolholders as a mainstay in some machine shops is more recent and owes much to the desire to overcome the limitations of other types of toolholders, according to Timothy Fara, managing director for Bilz Tool Co. Inc., Lombard, Ill. In the 1980s, he said, endmill holders were the predominant toolholders in the marketplace. Early collet chucks were too limiting, in that they were only suitable for drilling applications, and while the early 1990s saw the rise of single-angle collets like the Erickson TG (Tremendous Grip), which allowed for greater gripping strength and the ability to handle radial loads, they weren’t ideal for all applications.

“One problem with the Erickson TG collets started when we began to push the feed rates to keep up with the jobs, which would cause the tools to move around,” Fara said. “So, different types of collets were created to account for different types of jobs, which is when the hydraulic chuck really started to catch on.”

Courtesy of Hydra-Lock

From left to right, a special flange-mounted hydraulic holder and two hydraulic holders with standard shank mountings.

The main advantage of hydraulic toolholders is their ability to securely grip the tool shank, which reduces TIR. “The industry was looking for lower TIR, something that would hold a cutting tool closer to the center line,” Fara said. “The main reason for that is that for every 0.001 ” the tool goes off center, you [immediately] sacrifice 10 percent of your tool life because chip load is no longer evenly divided amongst the flutes of the cutting tool. Whatever side is offset takes the brunt of the chip load, so wear is accelerated because there is more work being done by one side of the endmill than the other. Hydraulic toolholders, with their extremely tight TIR, were an answer to that.”

Similar to other types of tooling, a variety of hydraulic toolholder classes are available. For example, Hydra-Lock offers three: Class A uses a solid-steel expanding sleeve, Class B uses a slit-steel expanding sleeve for greater expansion for a given pressure, and Class C uses the company’s Hydra-Fibre plastic material in the sleeve and is for holding thin-walled and out-of-round parts or tools.

Schunk’s TENDO series of hydraulic toolholders also is available in three different levels. The entry-level EC line, according to Panosh, is only available in sleevable diameters and not repairable. The Platinum line, made from through-hardened tool steel, is available in a range of sizes, both sleevable and direct-clamping. The Tech line consists of application-specific specials.

Alternative Nation

Despite their advantages, some toolholder manufacturers have stopped selling hydraulic units in favor of mechanical or thermal alternatives.

“About 8 years ago, we moved our toolholder focus almost exclusively to milling chucks,” said Scot Irie, product manager at Lyndex-Nikken Inc., Mundelein, Ill. “Early hydraulic chucks had no shutoff system, which resulted in internal leakage of hydraulic fluid, so we transferred our efforts to milling chucks.”

Courtesy of BIG Kaiser Precision Tooling