Multiaxis turning centers question(s)

I hope I don't cause a disturbance in the flow by asking an "on topic" question!
When would a sub-spindle be needed? Can it also be used as a tailstock?
What is the C axis? I'm guessing it's the rotational positioning of the sub-spindle or is it the live tooling axis?
Can a radial thread be put in with live tooling? I'm thinking it would require an encoder on the tooling drive. Machine dependent?
Thanks, Dave
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Any time you want to do turning or milling on the backside of a part. It can be used to grip and sync turn, supporting the free end, yes.

C-axis is the rotational positioning of *either* the main or sub spindle. In this mode, a spindle turns into a 'c-axis' indexer, much like a 4th axis on a mill.

Yes, it can. You don't actually *have* to have an encoder, if you use a tapping head, but most machines now have the rigid tap option on the live tools.
--
Anthony

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Thanks for your reply Anthony. I noticed OD tool holders with places on both sides, makes sense now. So the idea of the extra features is to do as much work on one machine verses moving the turned part to a mill or swapping ends to turn the back side.
Dave

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Dave
One other real benefits of a multiaxis turning centre is the ability to keep tolerances tight and parts very consistent. With that said, a machine like this requires a different planning and operating process as well because you could now be turning and milling all at one go, so you can't afford to have tools fail if you are leaving the thing alone for an hour or 2.
Rgds
Adrian
On Mon, 02 Feb 2009 11:19:34 -0600, Dave W wrote:

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