Turning Long Thin Walled Tubes
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    Default Turning Long Thin Walled Tubes

    Hi All,

    Looking for some tips on turning some long thin walled tubes. I am running into a few issues.

    First is that the tubing is bowed, these tubes are about 36" long and 1.5" diameter. Some are better than others but ultimately its out of the question to find perfectly straight tubes. I have a follow rest for my 13x36 Clausing lathe but the tube nudges my whole carriage to the side as the high spot passes. Is there a way to shim the carriage back to tight tolerance on the ways? Or are these just forces a lathe isn't designed to take?

    let me know if anyone has any ideas..

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    Cut toward the tailstock, you will be turning it straight as you come to the high spot. Get it straight then you do what you want.

    Ed.

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    Quote Originally Posted by juggaloslaya View Post
    Hi All,

    Looking for some tips on turning some long thin walled tubes. I am running into a few issues.

    First is that the tubing is bowed, these tubes are about 36" long and 1.5" diameter. Some are better than others but ultimately its out of the question to find perfectly straight tubes. I have a follow rest for my 13x36 Clausing lathe but the tube nudges my whole carriage to the side as the high spot passes. Is there a way to shim the carriage back to tight tolerance on the ways? Or are these just forces a lathe isn't designed to take?

    let me know if anyone has any ideas..
    Are your gibs tight?

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    Can you straighten them before turning? Heat treat shops often have straightening presses.

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    If the carriage is being moved by the high spot you need to determine where it is loose, and why.

    What usually happens is the tubing bends away from the bit, and the diameter iws increased in the middle. The purpose of the steady rest is to trap the portion of the tubing just cut between the steady rest and the bit. This allows the diameter to cut the same along the length. This should also eliminate the high spot from being able to push the carriage. You need to be taking a full diameter cut at the tailstock end, then adjust the steady rest to touch this, then make the rest of the cut. It sounds like you have the steady rest before the cut, so it is being pushed by the high spot.

    How is the tail-stock end of the tubing being supported?
    What is the tubing material?
    What type of bit? Carbide? HSS?

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    Fill the tubes with Cerro metal ,melts at boiling water temp for reuse.

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    You might try driving a mandrel into the tube. This would straighten and support it.

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    idea #1 tighten the lathe down or fix how loose it is.
    #2 most tubes are nowhere near as straight as they seem to be, ever.

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    Also make sure you aren’t distorting/deflecting the tube in your chuck/collet. I turn full length (usually about 26”) thin stuff between centers pretty frequently; made a faceplate with a drive dog type thing, and that helped quite a bit.

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    Nudging the cross slide ?

    Use a smaller nose radius to lower the cutting forces.

    Also get rid of most "lead angle" or what ever you call it, and go with a almost
    square to the cut insert angle.

    Also, if you can, go with a positive rake to again "lower the cutting forces"

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    To followup on Digger Doug's comments.

    Consider grinding a bit just for this cut so you can easily control and modify the nose radius, rake angle, and angle of the cutting edge. Carbide "pushes" against the work more than HHS does, so try going to HSS. Even better yet, get some Tantung G. or one of the other cast alloy blanks.

    Cast Alloy Lathe Tools

    If you are going to use carbide, consider some of the high rake inserts designed for aluminum.

    One last thought. If nothing else is working for you, slow the speed down, hone the edge as sharp as you can get it (diamond if a carbide bit) and slather the bit and the work with Moly D tapping fluid.

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