Chatter issues on small OD part
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    Default Chatter issues on small OD part

    Hey guys, so I'm turning a part which is rather small and the stick out about six inches. I'm wondering what approach you guys would use to make this part? The test piece is 303 stainless and the part itself will be of inconel. I'm not quite sure if there will be a decrease in the chatter when I machine the inconel. Currently, I'm contour roughing the front rad with a vbgt with a .016" rad and leaving .01 in x and .005 on z. Next I'm roughing toward the second rad using a vbgt .0312 rad UM chipbreaker. Leaving .04 in x and .010 in z. The. Starting at the front of the first Rad, blending into it, and finishing at a .040 DOC at 255sfm and .0005 ipr using an vbgt .008. Will post a pic of the part and drawing in a minute once I figure out how to. Any advice will be great. Thanks guys.

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    Have you considered CNC swiss or other sliding headstock machine?

    What is "rather small"?

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    Without looking at a picture or print I would suggest trying to cut the part in a single pass.

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    .160" over 4.2". Needs a 16 finish.

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    A swiss machine (sliding headstock) or a lathe with twin turrets that allows for "pinch turning" would be my suggestion.
    That probably doesn't help YOU with the part, I know.

    Inco needs to be setup correctly, and machined aggressively.
    A long, thin part, with tight tolerances and fine finishes, is going to be a nightmare!

    Doug.

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    Doug,
    Do you mean twin spindles? Hang on to both ends in chucks or collets and turn between them is what i am thinking.

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    Quote Originally Posted by RJT View Post
    Doug,
    Do you mean twin spindles? Hang on to both ends in chucks or collets and turn between them is what i am thinking.
    No he means twin turrets, for pinch turning, so that you're essentially balancing the forces on the OD of the part, making it easier to keep it straight and in tolerance. Like this: YouTube

    But really, this sounds like a Swiss part...

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    Quote Originally Posted by Tupper87 View Post
    Hey guys, so I'm turning a part which is rather small and the stick out about six inches. I'm wondering what approach you guys would use to make this part? The test piece is 303 stainless and the part itself will be of inconel. I'm not quite sure if there will be a decrease in the chatter when I machine the inconel. Currently, I'm contour roughing the front rad with a vbgt with a .016" rad and leaving .01 in x and .005 on z. Next I'm roughing toward the second rad using a vbgt .0312 rad UM chipbreaker. Leaving .04 in x and .010 in z. The. Starting at the front of the first Rad, blending into it, and finishing at a .040 DOC at 255sfm and .0005 ipr using an vbgt .008. Will post a pic of the part and drawing in a minute once I figure out how to. Any advice will be great. Thanks guys.

    Ok, so I have never cut iconel so I could be FOS with this. Isn't .01" in Z and .04" (doc, so .08" on diameter?) in X a little excessive for finishing? Also, .0005 ipr seems way too low, but again, I've not cut this stuff so maybe that is right?

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    It is a Swiss part. But you gotta get through it, right? Your feed is way too slow. Do you have a Tailstock? There are ways to set up a sort of make-shift Steady rest. But you need to support it somehow. You could try a Swiss methodology where you Turn segments, then pull the part out as you go.

    R

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    Even if you don't pull it out out a bit at a time, turning it a bit at a time may help, especially if the stock is significantly oversize. That way the full stock diameter provides rigidity for the area you're working on at each stage.

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    A creative follow-rest. Maybe even two of them... one for turning in one direction, and then another tool / follow-rest for finishing up the neck in the other direction.

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    How many do you have to make and what time frame? That should dictate course of action. It is an obvious Swiss job. You could also rough them out, send them out to grind diameters and then finish the threads. If you have to make 10 of them and you fight it all week and they still look ugly what have you saved over outsourcing to someone with the right equipment for the job?

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    Quote Originally Posted by doug925 View Post
    A swiss machine (sliding headstock) or a lathe with twin turrets that allows for "pinch turning" would be my suggestion.
    That probably doesn't help YOU with the part, I know.

    Inco needs to be setup correctly, and machined aggressively.
    A long, thin part, with tight tolerances and fine finishes, is going to be a nightmare!

    Doug.
    I do have twin turrets. Which I am going to use when the piece comes back from stress relief. The finally OD needs to be .160" so I'll be taking it from .180 down. Hopefully this helps. The only thing I'm unsure of is do I try and pinch turn with an svvbn and finish the entire thing. Or use left and right tools and blend them at the rads. Any thoughts on which would be better? I'm thinking the svvbn would cause more chatter?

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    Quote Originally Posted by precisionmetal View Post
    A creative follow-rest. Maybe even two of them... one for turning in one direction, and then another tool / follow-rest for finishing up the neck in the other direction.
    I wish I had one BUT I don't think my boss will spring for one atm....

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    Quote Originally Posted by precisionmetal View Post
    A creative follow-rest. Maybe even two of them... one for turning in one direction, and then another tool / follow-rest for finishing up the neck in the other direction.
    Quote Originally Posted by litlerob1 View Post
    It is a Swiss part. But you gotta get through it, right? Your feed is way too slow. Do you have a Tailstock? There are ways to set up a sort of make-shift Steady rest. But you need to support it somehow. You could try a Swiss methodology where you Turn segments, then pull the part out as you go.

    R
    That would be great but the .160 Od cannot have any Mark's as it's considered a weak point. I've tried turning it in segments but it leaves behind indications of where the cutter enters and exits... Unless there is a way to do this without any indications? I'm already a week into this... driving me absolutely nuts.

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    Quote Originally Posted by precisionmetal View Post
    A creative follow-rest. Maybe even two of them... one for turning in one direction, and then another tool / follow-rest for finishing up the neck in the other direction.
    Quote Originally Posted by mhajicek View Post
    Even if you don't pull it out out a bit at a time, turning it a bit at a time may help, especially if the stock is significantly oversize. That way the full stock diameter provides rigidity for the area you're working on at each stage.
    The stock size is .5" which absolutely sucks... The only issue I find with that is it leaves tiny indications of entrance and exit moves.. Unless I'm missing something?

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    You do it at Transition points, not just in the middle of a controlled feature. But it's not really a method for regular Lathes. So with a great deal of care, you can do it, but it takes time to get it dialed in.

    You need to support the end somehow. BTW you are never going to Pinch a .16" diameter that long. NEVER in a Million years, without support. Right now you need to get it Roughed out to .02" over, so one step at a time. The witness marks don't matter on the rough part. Chatter doesn't matter on the rough part. So just get it to HT for now. After that, support the end one way or another, build a Follow rest that bolts onto your toolholder out of UHMW or something if you want, but you need to support the part. Change your insert to a .001" radius, slow the spindle down to painful, and feed about 10% of the insert radius.

    R

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    Quote Originally Posted by precisionmetal View Post
    A creative follow-rest. Maybe even two of them... one for turning in one direction, and then another tool / follow-rest for finishing up the neck in the other direction.
    Quote Originally Posted by litlerob1 View Post
    You do it at Transition points, not just in the middle of a controlled feature. But it's not really a method for regular Lathes. So with a great deal of care, you can do it, but it takes time to get it dialed in.

    You need to support the end somehow. BTW you are never going to Pinch a .16" diameter that long. NEVER in a Million years, without support. Right now you need to get it Roughed out to .02" over, so one step at a time. The witness marks don't matter on the rough part. Chatter doesn't matter on the rough part. So just get it to HT for now. After that, support the end one way or another, build a Follow rest that bolts onto your toolholder out of UHMW or something if you want, but you need to support the part. Change your insert to a .001" radius, slow the spindle down to painful, and feed about 10% of the insert radius.

    R
    Thank you for the input I was thinking .004 rad in a positive insert I'd need to go to smaller tool holders to get a the rad smaller... I'm still kind of a noob when it comes to these kind of parts so bare with me. You don't think the tailstock alone will be enough support? How would I make a steady rest? I'd need some sort of bearing no? If you wouldn't mind, could you explain how one would eliminate witness marks if I were to machine it in segments?

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    Thank you everyone for the advice. I really appreciate it!


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