Collet chucks are a familiar tool in metalworking and wood workshops all over the world. They will usually be found alongside the 3-jaw and 4-jaw chucks of lathes and milling machines.

General purpose and specialized chucks come in a great variety of types, sizes and names. Depending on the job at hand, you could be using a magnetic, air, collet, vacuum, gear, jaw, lever, clamping, universal, woodworking, safety, milling, lathe, roto-clamp, electrostatic, grinding, core, drawbar, speed, spindle, diaphragm, precision, spinning, tap, power, pulldown, Jacobs, eccentric, roll, scroll or hydraulic chuck .. and I'm sure there are quite a few more.

In our engineering workshop, although the jobs were many and varied, we almost only ever used the jaw chuck (3 and 4-jaw,) and the collet chuck.

When comparing the collet chuck to the jaw chuck there are advantages and disadvantages that must be taken into consideration before deciding on the best choice for any given job.

Advantages of the collet chuck:

* Powerful clamping force. Whereas the jaw chuck has only a few points of contact on the workpiece, the collet chuck contacts the entire circumference.

* High speed stability as a result of lower spindle load and less effect from centrifugal force. At very high speeds, the extra mass of a regular jaw chuck has a longer acceleration time, the spindle bearing loads are greater and the effect of centrifugal force is to reduce the initial clamping force.

* Resistance against accidental knocking and jarring. The greater surface contact area of the gripping force results is a more stable clamping of the tool or workpiece.

* Speed of installing or replacing the chuck. This is a major consideration in mass production work. A collet changeover could take just 15 seconds - compared to possibly 15 minutes or more for a manual jaw chuck swap-over.

* Precision self-centering. As a result of the clamping force contacting the entire circumference of the tool or workpiece, self-centering is more accurate than in the case of a jaw chuck which has fewer points of contact.

* More secure pipe and tube work. The risk of crushing or denting thin-walled materials is greatly reduced by the even distribution of the 360 degree contact.

Disadvantages of the collet chuck:

* Narrow range. Each individual collet has a limited clamping range - so to cover a wide variety of workpiece or tool sizes, many collets will be required. This can add up to quite an expense.

* Job size limitation. Collets are best suited to smaller sized workpieces or tool shanks - usually no larger than 3" diameter.

The most popular collet chuck is type that grips the outside of a tool shank or cylindrical workpiece for machining. There is also an inside-holding variety which facilitates machining of the entire outside surface. Custom shapes are also available for holding square and hexagonal etc. stock.

Some of the industrial standard collet chucks are named 5C, 16C, 20C, 25C and R8.

The typical collet chuck has a parallel cylindrical surface on the inside and a conical surface on the outside. It has longitudinal grooves to allow for expansion and contraction when either 'pushed' with a threaded taper cap at the front end or 'pulled' at the back end. The clamping effect is produced by forcing the collet into a matching tapered socket which contracts the collet and efficiently grips the workpiece or tool.

Some of the names manufacturing quality collet chucks for the market today are Hardinge, Techniks, Skill-Craft, Royal, Lexair, and Riten