When you purchase a CNC lathe or turning centre the machine will usually come equipped with a three-jaw power chuck as its workholding system. These useful devices allow for a variety of applications; operating at midrange rotational speeds, providing good accuracy and also the capacity to grip a wide range of part sizes. However, three-jaw chucks are not the answer to every machining situation and as such there are a variety of alternative workholding options. Perhaps the most popular and common amongst these are collet chucks.
Collet chucks were initially developed to assist in the machining of smaller parts and are now frequently used on workpieces with a diameter of about 80mm or less. However, it is possible to source collet chucks with a capacity of around 150mm for larger workpiece applications. The benefits offered by collet chucks when machining workpieces with a diameter below the 80mm mark mean that some machine tool and lathe manufacturers now install them as standard.
Perhaps the biggest advantage that they provide when machining smaller parts is the increased tool clearance delivered through the sleek shape and compact nose diameter. The setup allows for the machining process to occur closer to the chuck, which serves to increase rigidity and improve surface finish on the workpiece.
Another reason that collet chucks are so well suited to the machining of smaller parts is that they are both symmetrical and have a lower mass when compared to traditional three-jaw chucks, which enables them to operate at greater revolutions per minute. Due to the fact collet chucks are somewhat lighter than three-jaw chucks, they are not as prone to the influence of centrifugal force; thus delivering a more stable gripping force throughout the range of turning speeds.
One of the key ways that collet chucks differ from three-jaw chucks is that they provide support to the workpiece around 360 degrees, as opposed to having just three points of contact. Even distribution of the gripping force means that the workpiece is less likely to slip and also reduces the chances of distortion; a huge benefit when manufacturing tubes or parts with thin walls.
In addition to the benefits that we have already touched on, there are several other benefits that collet chucks provide, such as reduced vibration when bar feeding and improved clamping and unclamping speed. In addition, custom collets can be utilised for the holding of irregular shaped parts.