cnc turned parts-Collets and Mandrels

 
Quite a few different collet systems are to be found in workshops. Some are used for holding tools such as milling cutters, some are used for bar or workpieces, while some may be used with both bar and workpieces.
 
One of the commonest is the ER collet, which comes in several different sizes, each having a different large diameter. The ER collet system allows up to 0.039in (1mm) collapse of a collet, although in the smaller sizes you can buy the collets in
0.5mm increments. A 16mm collet, for example, will hold round material down to 15mm diameter. Whatever the ER collet size, they all appear to go down to 1mm minimum, which will close down to 0.5mm.
 
There are many types and sizes of ER holder available. All the usual Morse taper shank sizes are available and you can also buy various diameters of extended par- allel shank holders. that have a short shank, but because you need to use the holder with a drawbar, you can’t put long bar stock right through them. To overcome this, for lathe work you can also buy ER collet holders designed to be fitted to a chuck backplate that you can machine to suit your lathe, so ensuring good concentricity. Because they don’t use a drawbar, you can fit bar stock right through and into the headstock mandrel.