How to Choose Between Grooved (Serrated) and Smooth Bore for Main and Sub Spindle

Collet Selection Guide – Main vs. Sub Spindle:

Main Collet Mostly will made with a grooved (Serrated) bore ,cuz Main collet is for first operation in the main spindle to clamp the bar rod.So it might be required more clamping power.
Sub Collet mostly will made with a smooth bore , cuz sub collet is used for second ooperation in the sub spindle to pick up the semi-finshed component, and it will clamp the finised side , so it might be required to protect the surface of the part.
Many swiss sliding head lathe will use the same type collet both for main spindle and sub spindle , like Tornos gt26 use the F30 76-101 (0161) type collet for both main-spindle and sub-spindle , but as i said at above 1 & 2, even they use the same type collet, but main collet mostly use grooved bore, sub collet use smooth bore.For some swiss lathe, like Tsugami 20, their might use two type collet ,one for main-spindle , the other for sub spindle.
When the bore size is within 6.0mm, whatever main spindle or sub spindle collet, all will be smooth bore, and it is also available for clamping bar rod in main spindle or semi-finished part on sub spindle.
When we making the main collet and sub collet, the technology will be not the same. for main collet, we will consider its clamping force and operation in swiss turning, then the open amount will bigger than the sub – spindle collet.
At the mean time, for sub collet, we will consider it protection request, so the open amount of the end of the collet will smaller than the main collet, and it will also be made to a more precision collet.