New Chuck Standards Take Hold

At their best, industry standards promote progress and deliver benefits. Good standards are welcomed. They make a positive difference to all interested parties.

A new set of standards for lathe chucks and chuck jaws that is nearing completion appears to be this sort of welcome development. The section about chuck safety is especially important and breaks new ground in establishing who is responsible for safe chuck operation. So the new standards are more than a much needed update; they make a substantial contribution to the resources that chuck manufacturers, machine tool builders and end users can draw from for more effective application of these critical workholding devices.

 

Reflecting Current Trends

Chucks are a critical part of a lathe setup, but like most workholding devices, they do not always get immediate consideration in process planning or design. Yet current trends in turning operations are amplifying the role of the chuck. Typical spindle speeds are considerably higher than ever before, for example. These higher speeds increase the forces acting on the chuck's clamping power. Likewise, spindles tend to accelerate at much faster rates than in the past.

Tolerances on workpieces are tighter and workpieces are more likely to have thin walls or delicate features, making distortion from clamping forces in the chuck more troublesome. The move to lean manufacturing has heightened interest in part loading and unloading, drawing attention to ways in which a chuck lends itself to streamlined, error-proof operation. The lathe chuck has to be part of the solution, not part of the problem.

None of these trends were influential when the last effort to formulate chuck standards was completed in 1972. At that time, the effort was limited to updating chuck standards originally created almost 50 years earlier.

In 1992, a group of manufacturers of workholding equipment (mostly of rotating devices such as chucks and related items) began to discuss the formation of a trade association to represent their interests. This association would speak for members in a uniform voice, collect sales statistics, distribute marketing data and coordinate standards-making activities. The group ultimately established itself as the Workholding Products Group (WPG), which operates under the auspices of AMT—The Association For Manufacturing Technology in McLean, Virginia. (This box highlights the data gathering activities of the WPG.)

Because standards making was a priority, the group revived Technical Committee (TC) 11 in order to review existing standards governing chucks and chuck jaws. TC11 was originally formed in 1928 as part of Sectional Committee B5, a body dedicated to standards for "small tools and machine tool elements" under what is now the American Society of Mechanical Engineers (ASME). This particular committee had been dormant since 1972.

The revived chuck standards committee began meeting in 1996, usually convening two or three times a year to review the progress of ongoing projects. All of its members are volunteers, mostly from companies in AMT's Workholding Products Group. Early on, the committee recognized that it should revamp the standards for chucks and chuck jaws not only to meet the needs of chuck makers, but also to meet the needs of machine tool builders and end users. Five main standards-making areas were identified:

• Chuck terminology
• Chuck performance checks
• Chuck safety
• Chuck jaws
• Spindle interfaces

They make up the five sections proposed for the new standard.

Because putting forth standards is a multi-year effort, the work of this committee has come to fruition only in the last several years. However, substantial progress has been made on the first four sections, and the last one is well underway.

 

The Current Standard

The very first thing the committee did was review the 1972 revision of the standard. The group saw that this document had important historical value. Many of its provisions had governed the manufacturing of chucks and chuck jaws for decades. Numerous products manufactured to comply with this standard are still in daily use across America. For these products, the standard would continue to have value as a reference work for documenting compliance issues related to product use and performance.

Thus, the committee's initial immediate activity was to re-issue this document with updates to reflect current conditions and usage. This update was approved in January 2001. (B5.8 Chuck and Chuck Jaws can be ordered from ASME at www.asme.org or by calling 1-800-843- 2763.)

In the meantime, the committee got to work on the five sections planned for the new standard. The first of these was the section that defined chuck and chuck jaw terminology.

Terminology

 

Although the basic components in each type of chuck are similar from brand to brand, different manufacturers sometimes use different names for these components. To avoid confusion, the committee adopted a glossary of terms pertaining to chucks. Precise definitions for these terms were agreed upon. These terms were subsequently used throughout the other sections of the standard so that usage was uniform and unambiguous. Thus, provisions in the standard are less likely to be misinterpreted or misunderstood.

 

Performance Checks

The thrust of this section of the standard is to describe how chuck manufacturers should check the performance of their products. By conducting these checking procedures in the same manner, manufacturers can report results that chuck buyers can use to compare chucks and match them appropriately to the application. Standardized performance checks also make it easier for chuck buyers to identify inferior products being offered by unqualified manufacturers.

 

Safety

The section about chuck safety ("Safety Code of Practice") is remarkable for several reasons. It is an entirely new addition to the proposed chuck standard. Committee members believe that this section makes the United States the first country to include chuck safety in a chuck standard. According to Spencer Hastert, who headed the subcommittee that formulated this safety code, the standard takes a fresh approach. It recognizes that responsibility for the safe use of chucks is shared by the chuck manufacturer, the OEM who installs a chuck on a machine tool and the end user.

"End users have to take an active role in protecting their own safety," says Mr. Hastert, "so acknowledging this is an integral part of the code."

Because chucks and chuck top jaws come in a variety of types and styles, the safety code does not dictate how manufacturers must design or construct chucks and jaws. It simply specifies the general requirements that design and construction must meet. For example, the code does not set specific values for input force, stroke length or speed of actuating equipment. Instead, it requires manufacturers to make sure that these values are compatible with the chuck.

Likewise, the code does not dictate weight, position or speed limitations for top jaw configurations; it merely requires that top jaw design address these limits. Other critical design characteristics of chucks and jaws are treated in a similar fashion.

The safety code spells out what safety instructions must be provided by original chuck manufacturers and by original top jaw manufacturers. Here again, the code does not prescribe specific values such as maximum drawbar pull, static gripping force or maximum rotation speed, but it does require that manufacturers provide these values in their instruction manuals. However, the code includes a series of appendices that gives formulas and outlines procedures for determining these chuck forces.

A similar approach is applied to machine tool builder responsibilities and end user responsibilities. Builders are responsible for selecting a chuck that is compatible with the machine tool's cutting capabilities, but this compatibility is not defined in numerical terms. All of the issues that the builder must address in safety instructions are listed, but it is left to the builder to determine how much detail to include. Finally, the builder must provide a safety placard that not only identifies the chuck make and model number, but also gives maximum input pressure in the cylinder and maximum rpm.

Workholding end users are admonished to read, understand and adhere to the instruction manual for the chuck. Other responsibilities include following proper maintenance procedures and regular checking of static gripping force. These activities must be documented. Samples of a maintenance schedule sheet and a grip force log sheet are given in the appendices.

This section of the standard has been submitted for industry comment and is now before the ASME for ratification and publication. "Implementing this safety code will go a long way to fill a gap in the technical information that is accessible to builders and users," says Mr. Hastert.

 

Jaw Mountings

The section on chuck jaw mountings describes the interfaces between top jaws and mounting surfaces on various types and sizes of chucks. The existing standard describes only two widely used types of interfaces, whereas the new standard describes seven of the most common types. Essentially, this section presents diagrams and tables listing all critical dimensions for mating features on master jaws and their matching interface on top jaws.

According to Chriss Mayfield, director of administration and training at Abbott Workholding Products (Manhattan, Kansas), a shop that makes its own top jaws will find these tables useful as guidelines to be sure that features such as the tongue and groove interface have correct dimensions and tolerances to fit the chuck, and so on. Mr. Mayfield, who headed the subcommittee that compiled this section of the standard, notes that a shop can also use the tables to reference specifications for top jaws ordered from suppliers. Compliance with this section will indicate the tolerances to which interfacing surfaces of top jaws have been produced.

Manufacturers of chucks and manufacturers of top jaws can follow the specifications to ensure compatibility between their products. "This is will be very useful to manufacturers of top jaws, such as Abbott," says Mr. Mayfield. "We have 35,000 part numbers, and this standard will help us meet customer demands for top jaws to fit the chucks in their shops."

The section has been submitted for industry comment and will be reviewed in light of these comments before being submitted to ASME for ratification and publication.

 

Spindle Interfaces

This section deals with how a chuck attaches to the spindle nose of a lathe. It will present diagrams and tables listing all critical dimensions and tolerances for mating surfaces between the chuck and the lathe spindle. This data will help chuck manufacturers and machine tool builders maintain compatibility between their products.

As of March 2005, the subcommittee assigned to this section had begun compiling data so that an initial draft of the section could be presented later this year. The subcommittee expects to have the completed document submitted for industry comment in early 2006.

 

Teamwork Pays Off

Although members of TC11 come from companies that compete with other companies represented on the committee, this rivalry is put aside during meetings and subcommittee work. In fact, the committee prides itself on its nonpartisan spirit of cooperation. Many members have become good friends over the years of working together.

The committee has also benefited from stable and effective leadership. Richard Spooner, president and CEO of Powerhold, Inc. (Middlefield, Connecticut) is the longtime chairman of the committee. His ability to coordinate its activities and keep the committee focused has much to do with its success. Mr. Spooner, however, credits the hard work of the individuals involved and the support of the companies that they represent for the committee's progress.