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The following article appeared in Cutting Tool Engineering, October, 1992, and was written by Steve Plottner.

While the interface between a machine tool spindle and the tool has been changed through the years to meet new demands, the widely accepted long-taper holder has remained the standard of the American National Standards Institute (ANSI) and the European-based International Stan dards Organization (ISO). Today, how ever, high-speed machining has placed different demands upon toolholders, and some users have called for a new toolholder design to meet these demands. In response, alternatives to the long- taper design have been introduced. Many toolmakers are trying to understand this new technology so they may begin to make use of it.

Much of this activity has taken place in Europe, where the Deutches Institut fur Normang eV, commonly called DIN, is currently considering a proposal for a new short-taper design. The draft proposal is expected to be printed and become a DIN standard within the next four months. The committee drafting this standard will, at that time, send a working document to the ISO for further study. DIN committee member Eugen Valerius of Kennametal, Germany says he expects the DIN standard to become an ISO standard within three years. While most toolmakers acknowledge the need for an alternative design, opinions vary regarding the viability of the design proposed by DIN as an international standard. Some say the new toolholder, with its short, hollow shank, will help revolutionize the industry, but questions remain about the broad-based usefulness of this toolholder or the industry's readiness to abandon old designs.

The original design for the hollow- shank toolholder grew out of the work of a committee comprised of major German end users (including Benz and Volkswagen), toolmakers, and machine tool builders. Working with the University of Aachen's Werkzeuglabor (WZL) tooling laboratory, under the administrative leadership of Dr. Manfred Week, the committee sought to develop a new unpatented toolholder design for high- speed machining. The group hoped an innovative design could overcome many of the difficulties encountered with long- taper tooling at high spindle speeds, such as loss of rigidity, insufficient accuracy, uneven expansion of the holder, and an inability to maintain position in the z-axis.

The research team discovered that a connection having positive face contact with the spindle solved many of these problems. As a result, they made sure the two hollow-shank holders they designed--a short-taper holder and a double-cylinder holder--achieved such contact by using a flanged face connection. A retention knob is not used. Because both toolholders can be built with a small or large flange, and with or without coolant pons, eight different shank configurations are possible. The short-taper design allows greater radial accuracy because of its centering characteristics. On the double-cylinder design, taper and facing both carry the loads. This makes exact production tolerances necessary. Both holders seem to do a better job as rpm increases, adjusting to tool movement during high-speed operations. As centrifugal force expands the spindle diameter at high speeds, the hollow- shank holder sucks deeper into the spindle more quickly than a long-taper holder. A puller mechanism pulls back on the holder's internal walls, urging the thin and expandable outer walls to swell. Stress is generated at the face-contact area, providing good stiffness.

According to Brian Baker, director of steel products at GTE Valenite Corp., the new design meets its developers' objectives. Baker has been working with the hollow-shank toolholder for more than 18 months, researching and developening a potential product for Valentine. and thc forces acting in front of the spindle offer less error." Baker cites the toolholder' s high bending-load absorption and high radial accuracy as reasons for its superior performance. Many toolmakers around the world in addition to GTE Valentine. are researching the hollow-shank design and are planning to manufacture systems using it. At least one toolholder, developed by A. Ott GmbH. is already being marketed and distributed in the United States. Advanced Machine and Engineering Co.. Rockford. IL. is the American marketer of the unit called the Project 2000 machine tool interface. Dan Springhorn, Advanced Machine's service manager, said the toolholder has been available in the United States for six months. Several units are being used on an experimental basis in operations around the country, according to Springhorn. Project 2000 promotional literature claims that, compared to the standard long-taper toolholder, the new hollow- shank version offers better repeatability, higher rigidity, increased holder force within the gripper system, and reduced deflection at higher loads. Of these benefits, according to Springhorn, rigidity contributes most to tool performance. The high static and dynamic stiffness obtained with the beating shoulder allows for higher machining capacity and deeper cutting.

Springhorn believes the hollow-shank design's advantages over the long-taper holder will lead to the eventual acceptance of the new toolholder around the world. "Within five years," says Springhorn, "the hollow-shank holder will be the standard in Europe. Within 10 years, it will be the standard in America." But Rick Neigoot, senior product specialist--modular tools, at Sandvik Coromant, Fair Lawn, NJ, cautions against rushing to make this new design a standard. "A standard," says Neigoot, "should be based on the long-accepted use of a system. The accepted standard should be mature, withstanding the test of time. This eliminates changes or modifications to the system." David Lewis, manager of rotating- tool engineering at Kennametal Inc.. Raleigh, NC, and chairman of the ANSI Technical Committee B 5/TC-45 (which defines and updates the American toolholder standard), plans to develop an American position on the hollow- shank toolholder before the year's end. His goal is to finish it in enough time for a plenary session of the ISO to read and discuss it. Lewis says that many factors will contribute to the further development and manufacture of this new toolholder design, as well as to its acceptance as a standard. One sure influence will be the economic consolidation of the European Community by 1993. "A lot of things need to be considered," says Lewis, "including what's good for companies and what's good for the industry."

Leading the movement to standardize the hollow-shank design is DIN. Committee-member Valerius says that last year the committee published four DIN draft standards, two for the double- cylinder design, with small and large flange, and two for the short-taper design, also with the two flanges. But in the original drafts, each combination had a number of coolant variations. "The DIN draft proposal contained 50 different options," says Valerius. The DIN committee sent the draft to ISO, but both groups expected difficulties with the broad variety of designs. In January 1992, DIN met again, this time reducing the diversity of short- taper options and deciding on one coolant-supply system for all hollow-shank designs. The present, somewhat slimmer, DIN draft proposal contains only 15 options, centering on the short-taper design with a small and large flange. The small-flange version is primarily for lathe applications, the larger flange for high-performance applications. Valerius is quick to point out that although DIN is expected to adopt the standard in four months and ISO is expected to follow suit within three years, this work is not meant to replace the current long-taper design. Both the DIN standard and the working document presented to ISO state that the short-taper design is an additional standard for high- precision, high-speed machining. In conventional applications, the long-taper holder is still to be used.

Sandvik Coromant's Neigoot sees the proliferation of standards as a major international problem. Neigoot argues that a standard should minimize a program (everything involved in the switchover to new tooling), yet end users who adopt the hollow-shank holder will have to increase inventory to make sure both hollow-shank and long-taper standard holders are on hand. They'll also require more machines--some that accept the long-taper holder, some that accept the hollow-shank version. The proposed DIN standards would further complicate a program because "the two types that are proposed have five or six sizes in each type--with and without coolant."

Neigoot wonders why the effort seems to be surrounded by a sense of urgency. "Is it for commercial reasons?" he asks. Neigoot is among those who believe that the producers of the new toolholders have a vested interest in accelerating the standardization process. Being an international standard would certainly lend credibility to a new product that users might otherwise view skeptically. But Anthony Bratkovich, engineering director at AMT--The Association For Manufacturing Technology, says there is a feeling among some in the industry that "we cannot afford to wait." There are two points of view, says Bratkovich. Countering those who believe the new design has not been tried enough are those who think enough testing has been done and the results show the new design to be reasonably sound from a technical viewpoint. "The international body may want to move quickly; there will be a million different modifications if they wait," he says. A lengthy wait may also give the Japanese a chance to take the lead in the development of these high-performance toolholders. Some German companies fear that a Japanese design instead of a German design could be the basis of a new worldwide standard unless the European organizations act soon. Even Valerius at Kennametal, Germany qualifies his optimism by saying the three- year timetable for ISO approval will happen "unless other countries, such as Japan, come up with something first." There are market forces, however, that may impede the development a acceptance of the hollow-shank hold, such as a lack of demand among general end users. While it is true that major end- users' needs drove the development the design, it is also tree that most e users are operating equipment that not benefit from the use of a hollow- shank toolholder. Most machines in the United States and abroad operate at speeds well below 20,000 rpm. End us- ers will continue using the long-taper toolholder on these machines for years to come.

At the very least, the cost of purchasing new machines that use the hollow- shank toolholder, or retrofitting older machines with new spindle mechanisms to accommodate the new design, will be weighed very carefully against any perceived benefits. For some, it may be very difficult to justify the cost of switching toolholder systems. As for toolholder manufacturers, several would like to see their own proprietary designs become standards. If a nonproprietary design like the DIN proposal is adopted as a standard, that design might become a commodity item.

Those who believe in the new toolholder design are confident the industry can overcome what they see as relatively minor hurdles. GTE Valenite's Baker suggests that people with a vested interest in current competing systems will naturally be the first ones to point out potential problems with the new design. "It won't be smooth sailing," he predicts. But despite this resistance, Baker believes that 50 to 60% of the machines worldwide will be using the new toolholder design within the next 10 years.

Acceptance will come first from the larger end users, who have the capital to invest in high-speed machine tools and new toolholder systems. Some end users in Europe are already using the new toolholder, and others are making plans to do so. GM Europe is among them. In the United States, the technology is just now emerging. "This really hasn't raised its head outside of Germant," says Dan Chattier of Command Corp. International, Minneapolis, a manufacturer of conventional toolholders. "So it's a hidden controversy here."

As toolmakers begin making use of the new nonproprietary design, various proprietary elements will begin to be included. For instance, Ott's Project 2000 includes a clamping arrangement that is patented by Ott. This does not change the actual shank, which, according to Valerius at Kennametal, Germany, will remain the nonproprietary design developed as the DIN standard. Consequently, end users will have a universal connection system. What this will mean in the marketplace remains to be seen. Although no one can predict the ultimate success of the new design, there is a place in the industry for the hollow- shank toolholder. In the high-speed lathe and turning markets, the benefits that can be gained in accuracy and rigidity do seem to outweigh the costs in changing over to the new system. This new design represents the first serious change in many years, and toolmakers, machine builders, and end users will need to study this innovation and decide for themselves if it's relevant for their operations. "It's very hard to have a revolution in this kind of thing," says Kennametal's David Lewis. But in a world of machining at 50,000 rpm, revolutions can occur very quickly.

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