3-jaw live chuck in tailstock .... unlock the tailstock?

borne2fly · Apr 16, 2011

I'm turning a part that's supported at both ends by chucks ..... a 4-jaw in the spindle and a bison 3-jaw live chuck in the tailstock. This is the first time I've used a live tailstock chuck. Workpiece is mild steel, 5" dia x 24" long. I've been told to unlock the tailstock so it can move on the ways in case the workpiece expands from heating. Does this sound right? I'm use to locking the tailstock because I mostly use a live center, so I figured the same thinking would apply to a live chuck. My fear is that the morse taper holding the chuck in the tailstock might come loose unless I lock it and keep a light pressure applied.

sicero · Apr 16, 2011

My thoughts would be, a death grip on the chuck or tailstock is not needed but I sure wouldn't leave it loose. Kenny

L Vanice · Apr 16, 2011

A loose tailstock to bed joint would lose rigidity and support on the end of the bar. The result would be chatter and loss of accuracy on the diameter of your cut. It would take a lot of cutting to get a bar that big hot. If you are really worried, you could wrap the end of the bar with one layer of greased thin steel shim to encourage the bar to slide axially in the jaws of the live chuck if it does want to expand. I would rather just avoid getting the bar very hot.

Larry

eKretz · Apr 16, 2011

Do not leave the tailstock unlocked. I use tailstock chucks in our lathes all the time. If the part were to get hot enough to cause that much growth, it will slide itself in the chuck jaw, there's no stopping it. At a length of only 20" you'd have to get it awfully darn hot to even need to worry about that. Use coolant and forget about it.

HuFlungDung · Apr 16, 2011

It really should not be necessary to apply end pressure when using a tailstock chuck. Lock the tailstock to the bed and back the quill out a little bit, and the backlash should provide plenty of distance for typical expansion of the workpiece. Its also very easy to feel if the pressure is getting high by tweaking the handwheel this way or that.

I assume this is a hollow workpiece, or why the chuck?

borne2fly · Apr 16, 2011

Yes, it's a hollow workpiece. It's also an excuse to try out that tailstock chuck

It's unanimous, lock the tailstock.

For a while there I actually considered leaving it unlocked, then I figured I better bounce this off the PM board, .... I hear all sorts of nutty things from people but you guys in here have always given sound advice. Thanks again!

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3-jaw live chuck in tailstock .... unlock the tailstock?

borne2fly

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sicero

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L Vanice

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eKretz

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HuFlungDung

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borne2fly

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