Thread Bar Project, nothing is going right and I need help

Yes, so can I fix my stock piece now or did I tighten it too much while I was turning? I tried loosening it and it still wobbled but I could loosen it more I think. I'm not sure, basically do I need to start another piece or can I somehow fix this one, because I spent a lot of time turning it.
 
jlsmithseven said:
I've use a #4 for this project and had to go almost right up to the end of the taper. Is that too deep? How do I know how deep to go, I thought it was 2/3 of the way up the taper.
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Drill in almost to the end of the taper on the center drill. This gives max support for the given center drill size. Do NOT go past the shoulder of the taper; if you do, the center will ride on the sharp edge and not the taper itself.

Remember that heat will expand the work piece so you have to check the tailstock pressure frequently when turning with dead centers. You only need enough pressure on the tailstock ram to keep the work piece fully engaged, and keep the centers lubed.
 
jlsmithseven said:
Yes, so can I fix my stock piece now or did I tighten it too much while I was turning? I tried loosening it and it still wobbled but I could loosen it more I think. I'm not sure, basically do I need to start another piece or can I somehow fix this one, because I spent a lot of time turning it.
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You might be able to save it but not knowing what it looks like right now, hard to say. I would try shaving off a small amount on each end and re-center drill it. This establishes a new taper for the centers. Then try to get the set up right and give it another try. If that fails, stay late after class and make a new bar.
 
I picked up something reading this thread. First, A thread bar it's an exercise that many schools use where a bar is turned to several diameters and each section is threaded.
You said you turned your center in the chuck on the machine and your part was fine. Next you said you can't always get on the same machine, that means you would need to make a new center every time you put the part in a machine. If you're moving the center you made with the part to a different machine it is not going to turn true . that is what I believe your problem is. If you move the part to a new machine you have to make a new center in that machine and not remove it until you're done with the part.
 
mark_f ....I have made the new center, I cut the 60 degree angle true every time.
the piece looks fine. it's just the smallest amount of wobble that will make the threads cut deeper on one side than the other. the piece is fully turned down , but I did manage to get a new center drill in one end right before the end of class today. on the face of this side, right next to the center drill hole, there was a tiny chip. like right on the outer edge, so i center drilled it until that little chip was removed and i went almost to the end of the taper like you said. im hoping this has fixed it, i didnt check yet but will tomorrow. thanks.
 
The pilot section of a common commercial center drill is far deeper than a center will ever reach for obvious reasons, as long as one drills past the pilot and less than the body one has made a perfect 60 Deg. center given the accuracy of the tool.
 
I think I'm tightening the tail stock way too hard. When I move my piece and the lathe dog, it barely has any give. Which in return means the lathe dog is not moving at all and sits in the same place while I'm spinning. Does that make sense?
 
JL, you have a teacher there, explain what is going on and get some help. It's very hard to say for sure if any one or more than one problem is causing your problem. You are paying for the tech school, so make them work for it. Testing is only one part of the course, recognizing you have a problem and need to understand why is both experience and the job of the teacher when you can't resolve it yourself, Then you can really work on the thread bar. Good luck.
 
jlsmithseven said:
I think I'm tightening the tail stock way too hard. When I move my piece and the lathe dog, it barely has any give. Which in return means the lathe dog is not moving at all and sits in the same place while I'm spinning. Does that make sense?
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That's tighter than it has to be. Back off pressure. Just snug it so there is no axial play; it will get tighter as the part heats up.

EDIT: I forgot that you're moving from lathe to lathe. Now that you've re-drilled your centers, don't forget to re-cut the taper on your headstock dead center after mounting it in the new lathe; this will get it concentric with the spindle.

Let us know how it goes.
 
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