Three-jaw chucks are the standard work holding device for most CNC lathe users. It is among the most widely used types of chuck in a variety of turning applications. However, that does not mean it is the best chuck for all jobs. A collet chuck is an alternate work holding device that also uses mechanical forces to hold a workpiece. While a collet chuck does not work with the same wide range of workpiece sizes that a jaw chuck can accommodate, it offers advantages in speed, accuracy, and productivity that may be crucial for certain jobs.

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What is a Collet Chuck?

The standard work holding system that comes with most CNC lathes and turning centers consists of a three-jaw power chuck, a hydraulic actuating cylinder, and a drawtube. The hydraulic cylinder is attached to the rear end of the spindle, while the chuck is mounted to the spindle&#;s front or working side. The cylinder and chuck are usually connected via a hollow, steel drawtube that passes through the spindle bore.

Similarly, a CNC collet chuck is mounted to the front of a CNC lathe spindle, using the machine&#;s existing cylinder and drawtube to actuate:

The axial motion of the hydraulic actuator&#;s piston is what causes the collet chuck&#;s jaws to open and close. The drawtube moves in unison with the piston, driving a wedge-shaped plunger within the chuck body as the piston slides back and forth. The plunger, in turn, converts axial motion to radial motion, accomplishing the opening and closing of the jaws. The gripping force of the jaws to a workpiece corresponds directly to the output of the actuator; thus, this force is easily regulated via a pressure valve.

Of course, a collet chuck requires a collet to function. Typically, collets have something like a 0.062&#; gripping range. Collets are readily available for round, hex, and square stock. A collet chuck can handle a fairly wide range of collets (e.g. 3/16&#; all the way through to 2-5/8&#;). Special collet requirements can be accommodated. Most modern collet chucks have a quick (e.g. 10 seconds) change functionality for reduced set-up times.

When is a Collet Chuck a Better Choice than a Three-Jaw Chuck?

• Bar Feeding: Collet chucks are ideal for machines equipped with bar feeders because they provide full 360° contact, ensuring that the bar stock remains on centerline and allowing for accurate re-gripping after being advanced. A collet chuck also helps to minimize vibration, and opens and closes faster than a three-jaw chuck.
• Small Diameter Work: Collet chucks offer much better tool clearance for small parts ranging in size from 1/16&#; to 4&#; in diameter. Collet chucks can also be run at higher speeds, and provide superior gripping force, than three-jaw chucks.
• Short / Thin Parts: A collet chuck&#;s low-profile design provides better tool clearance and allows for machining very close to the chuck face, which helps prevent thin parts from sagging or bending.
• High Speed Operation: Compared to three-jaw chucks, collet chucks hold up far better to the negative effects of centrifugal force. This allows collet chucks to run at higher speeds with consistent gripping force.
• Reduced Setup Times: A collet can be changed much faster than chuck jaws, and without boring. Collet chucks keep your machines making chips &#; and profits!
• Pipe and Tube Work: Collets provide 360° contact with the part, distributing the gripping force evenly around the part&#;s entire circumference and reducing the risk of crushing or distorting thin-walled parts.
• Odd Shaped Parts: With a bit of customization, collets can easily be made to hold off-shaped or off-center parts. There is a wide selection of standard collets designed for round, square, and hex stock.
• Better Tool Life: The paddlewheel-like shape of a three-jaw chuck can deflect coolant before it reaches the cutting tool tip, shortening tool life, whereas the streamlined shape of a collet chuck enables precise coolant delivery. Collet chucks also produce far less mist than three-jaw chucks.

Our preferred supplier partner for collet chucks is Royal Products. Royal provides a wide range of work holding options, including several lines of collet chucks.

For more information about the benefits of collet chucks and help selecting the right work holding device for your operation, contact us.

Collets 101: Understanding Types and Uses

Many people, if approached on the street and asked for a definition of a collet, would likely develop a blank stare. Collets are integral parts of machining, and yet so many don&#;t know what they are or misrepresent them as chucks. As T.M. Smith Tool is known for their quick change tool holding systems, they know a thing or two about collet types, their capacity and the significance of these misunderstood and often underappreciated devices.

What is a Collet?

A collet is a form of chuck, but it is not identical. While a chuck is tightened around an object, a collet utilizes clamping pressure by forming a collar around the object being held, holding it securely in place. This clamping force is typing applied through a tapered design that uses a sleeve and inner cylindrical surface. While there are varying designs, all collet types operate by being pressed over the element to be held, resulting in both accurate alignment and static friction. While the collet is not suitable for every tool and operation, it does allow for self-centering, resistance against loosening, fast-chucking and steady clamping pressure.

Collet Types for Woodworking and Metalworking

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As with any tool or chuck, there are a variety of collets, making them versatile clamping devices. However, in general, different collet types are used in two specific fields of construction and manufacturing.

• Woodworking

  
  

  
  

  It should come as no surprise that a collet is useful in woodworking, as it is a tool found in drill presses and other machinery. However, the collet is most often used in routers to hold the cutting bits in place. The collet is secured to the tool using a hexagonal collet nut, allowing it to be tightened or loosened to the motor arbor.

• Metalworking

  
  

  
  

  While woodworking may only have a few varieties of collets, metalworking uses many types with varying holding capacities. Granted, the standard metalworking collet is used for holding round bar or tools, but there are also hexagonal, square and other shaped collets for specific tasks and tools. In addition to the different shapes and styles, there are also e-collets and step collets. E-collets or soft collets are typically machined for a specific job while step collets are designed to hold larger pieces.

ER Collets

While there are several types of collets, ER collets are the gold standard when it comes to clamping systems. Developed by Rego-Fix and patented in , the ER collet is manufactured and used worldwide as one of the most trusted clamping systems. The er collet chuck derived its name by combining the already established E-collet with the first letter of the development brand &#; Rego-Fix. These collets come in a standard series ER-8 through ER-50 with each series number referring to the receptacles tapered diameter size in millimeters.

While the revamped design allowed for broader clamping usages and convenience, the geometry and spring design make the ER collet useful only for cylindrical parts, meaning that square and hexagonal pieces still require specialty collets, like the 5C. However, despite the drawbacks of the cylindrical design, this collet system is still widely accepted as the most versatile collet chuck system.

If you are confused about your collet or chuck needs, then it may pay to contact T.M. Smith Tool by calling a representative at 1-800-521-. They are experts in all your tool holding needs and have a variety of collet, chuck and quick change designs that may suit your manufacturing and production needs. Don&#;t waste another minute debating the differences between chucks and collets, or the value in upgrading or updating an old drill press or milling machine. Call and find a solution that works for your business needs today.

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