is a holding device—specifically, a subtype of chuck
A chuck is a specialized type of clamp used to hold an object, usually an object with radial symmetry, especially a cylindrical object. It is most commonly used to hold a rotating tool or a rotating workpiece...
—that forms a collar
Collar may refer to:Human neckwear:*Collar , the part of a garment that fastens around or frames the neck*Ruff collar*Slave collar*Collar , a device of any material placed around the neck of the submissive partner in BDSM...
around the object to be held and exerts a strong clamping force on the object when it is tightened, usually via a tapered outer collar. It may be used to hold a workpiece or a tool.
A collet is a sleeve with a (normally) cylindrical
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
inner surface and a conical
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
outer surface. The collet can be squeezed against a matching taper such that its inner surface contracts to a slightly smaller diameter, squeezing the tool or workpiece whose secure holding is desired. Most often this is achieved with a spring collet, made of spring steel
Spring steel is a low alloy, medium carbon steel or high carbon steel with a very high yield strength. This allows objects made of spring steel to return to their original shape despite significant bending or twisting.-Grades:...
, with one or more kerf
Kerf and similar can mean:* kerf, the width of a cut* Kerf, a poetry collection by Peter Sanger* Kerala E.N.T. Research Foundation , a hospital at Kollam in Kerala in India...
cuts along its length to allow it to expand and contract. An alternative collet design is one that has several tapered steel blocks (essentially tapered gauge blocks) held in circular position (like the points of a star
A star is an ideograph whose outer edge forms a symmetrical polygon whose vertices alternate between joining outward- and inward-pointing pairs of edges. The figure may be the border or interior of the polygon, or one or more closed polygonal paths that include all of the border and also have some...
, or indeed the jaws of a jawed chuck) by a flexible binding medium (typically synthetic
Synthetic rubber is is any type of artificial elastomer, invariably a polymer. An elastomer is a material with the mechanical property that it can undergo much more elastic deformation under stress than most materials and still return to its previous size without permanent deformation...
or natural rubber). The Jacobs Rubber-Flex brand is a name that most machinists would recognize for this type of collet chuck system. Regardless of the collet design, the operating principle is the same: squeeze the collet against the tool or workpiece to be held, resulting in high static friction. Under correct conditions, it holds quite securely.
Generally, a collet chuck
, considered as a unit, consists of a tapered receiving sleeve (often integral with the machine spindle), the collet proper (usually made of spring steel), which is inserted into the receiving sleeve, and (often) a cap that screws over the collet, clamping it via another taper.
Usually in shop-floor terminology, the terms collet
are used in contradistinction; users speak of holding a workpiece or tool with either a collet or a chuck. In this context "chuck" means any type of chuck other than
a collet chuck (scroll chuck, independent-jaw chuck, etc.).
Advantages and disadvantages compared to other types of chuck
Each collet generally has only a narrow clamping range, which means that a large number of collets are required to hold a given range of materials in the chuck, unlike with many other types of chuck that will generally cover a wide range of sizes. This gives collet chucks the disadvantage of relatively high capital cost
Capital costs are costs incurred on the purchase of land, buildings, construction and equipment to be used in the production of goods or the rendering of services, in other words, the total cost needed to bring a project to a commercially operable status. However, capital costs are not limited to...
The collet's advantage over other chucks is that it manages to combine all of the following traits into one chuck, and this combination is highly valuable in an environment of repetitive part production:
- Speed of chucking (unclamp one part, switch to a new part, reclamp)
- Strong clamping force
- Resistance against being jarred loose (untightened)
- Centering at a high level of precision (runout is less than 0.005 in (0.0127 cm) TIR)
Of the above traits, scroll chucks offer always № 1 and № 2; usually № 3; to varying extents № 4 (depending on the situation); but not reliably № 5. Independent-jaw chucks offer always № 3; usually № 4; reliably № 5 (but at the expense of paying a skilled user to spend time achieving it); never № 2; and generally not № 1. Meanwhile, a collet chuck can deliver all 5 reliably, and with no need for a skilled user. (№s 3 to 5 do depend on the object being clamped closely matching the size and shape of the collet's clamping surface. This constraint is usually not a problem when the object is good-quality bar stock; the shank of a non-abused drill bit, reamer, endmill, etc.; or a previously machined part that is being rechucked for additional cutting operations.)
On a wood router
A router is a tool used to rout out an area in the face of a relatively hard workpiece, typically of wood or plastic. The main application of routers is in woodworking, especially cabinetry....
(a hand-held or table-mounted power tool used in woodworking
Woodworking is the process of building, making or carving something using wood.-History:Along with stone, mud, and animal parts, wood was one of the first materials worked by early humans. Microwear analysis of the Mousterian stone tools used by the Neanderthals show that many were used to work wood...
), the collet is what holds the bit in place. In the U.S. it is generally for 0.25 or bits, while in Europe bits are most commonly 6 or. The collet is hexagonal on the outside so it can be tightened or loosened with a standard wrench
A wrench or spanner is a tool used to provide grip and mechanical advantage in applying torque to turn objects—usually rotary fasteners, such as nuts and bolts—or keep them from turning....
, and has threads on the inside so it can be screwed on to the motor arbor.
There are hundreds of designs of collet used in the metalworking industry. Common industry-standard designs for manual mills are 5C and R8, however most are proprietary designs that only fit one specific manufacturer's equipment. Collets can range in holding capacity from zero to several inches in diameter. The most common type of collet is one that grips a round bar or tool, but there are collets for square, hexagonal, and other shapes. In addition to the outside-holding collets that are so common, there are collets that are used for holding a part on its inside surface so that it can be machined on its outside surface (basically, akin to an expanding mandrel
A mandrel is one of the following:* an object used to shape machined work.* a tool component that grips or clamps materials to be machined.* a tool component that can be used to grip other moving tool components.- Variants :...
). Furthermore, it is not uncommon for users to make a custom (bespoke) collet to hold any unusual size or shape of part. These are often called emergency collets
) or soft collets
(from the fact that they are bought in a soft (non-hardened) machinable state and cut as needed to fit). Yet another type of collet is a step collet
, which steps up to a larger diameter from the spindle (analogous to how a mushroom cap is larger than the stem). Step collets allow the holding of rather large workpieces, as long as they need not pass into the spindle through-hole—for example, disc-shaped workpieces.
In the accompanying photo, the two top left collets are the side and end view of one style of collet; the two right collets are from a smaller range. The lower image is of a disassembled pin chuck that is used to hold small drills or workpieces. The leftmost part is the body
, the collet
is shown protruding from the body, and the nose cap
is separate, on the right.
In use, the part to be held is inserted into the collet, and then the collet is pushed (via a nose cap) or pulled (via a drawbar) fully into the body (which has a taper to match the collet machined into the front). When the nose cap or drawbar is tightened properly, enough force is applied to the collet that the tapers at the front and back of the collet are pushed into their matching tapers, causing the collet to constrict in diameter. This constriction exerts considerable force onto the shank of the workpiece or tool that is being held in the collet. It is then securely held against any forces it may encounter during normal operation.
Many users (hobbyists, graphic artists, architects, students, and others) may be familiar with collets as the part of an X-Acto
X-Acto is a brand name for a variety of cutting tools and office products owned by Elmer's Products, Inc. Cutting tools include hobby and utility knives, saws, carving tools and many small-scale precision knives used for crafts and other applications....
or equivalent knife that holds the blade. Another common example is the collet that holds the bits of a Dremel
Dremel is a brand of power tools known primarily for their rotary tools. The tools were originally developed by Albert J. Dremel, who founded the Dremel Company in 1932 in Racine, Wisconsin. In 1993, the company was purchased by Robert Bosch GmbH, and today it is a division of the Robert Bosch Tool...
or equivalent rotary file.
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
industry, a die collet is used for picking a die
A die in the context of integrated circuits is a small block of semiconducting material, on which a given functional circuit is fabricated.Typically, integrated circuits are produced in large batches on a single wafer of electronic-grade silicon or other semiconductor through processes such as...
up from a wafer
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...
after die cutting process has finished, and bonding
Wire bonding is the primary method of making interconnections between an integrated circuit and a printed circuit board during semiconductor device fabrication. Although less common, wire bonding can be used to connect an IC to other electronics or to connect from one PCB to another...
it into a package.
Some of them are made with rubber, and use vacuum for picking.
Internal combustion engines
The two halves of the collar which fits around the stem of a valve and traps the spring
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...
against the cylinder head
In an internal combustion engine, the cylinder head sits above the cylinders on top of the cylinder block. It closes in the top of the cylinder, forming the combustion chamber. This joint is sealed by a head gasket...
are known as split collets.