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  • A question about lathe/work-piece setup

    Bear with me fellows,

    I’m about to ask a question that likely make little sense.

    Let’s assume you have a 12” long 2” diameter (or even longer) round prefabricated part that CAN be held in a lathe’s 4-jaw chuck but is too large to fit inside the spindle. The piece mics the same diameter at both ends and holds true at any distance between the two ends. You need to do some work on the end; just pick a need ….. turning the end OD a little or boring a hole in the end as an example.

    When you set up the piece, it is required that the piece be dialed in and run true. The problem is, if it’s dialed in next to the chuck’s jaws, run-out is .015” at the end. If you dial in at the end, run-out is .015” at the jaws.

    What is the correct way of setting up this piece. Do you dial in at the end where you will be working and damned the area being held by the chuck? Lets make it a little more difficult, the work piece is a pipe with the ID being too large and too thin to run a live center. What now?

    Harold
    For those having fought for it, Freedom has a flavor the protected will never know.
    Freedom is only one generation away from extinction.

  • #2
    At 12" long you need to support the outboard end with a steady rest...and dial in both ends!

    David
    David Kaiser
    “You can have peace. Or you can have freedom. Don't ever count on having both at once.”
    ― Robert A. Heinlein

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    • #3
      I would first find a bull nose live center big enough to fit the workpiece, or turn up a piece to fit into the end of the workpiece such that you can you can use a live center (or dead center) to hold the tail end true. Use a steady rest. Use the tailstock center and your 4 jaw to dial everything in, then set up your steady rest, remove tailstock, go to work.

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      • #4
        SUPER!

        Now a followup question. How do you keep the steady rest from marring the area where it is riding? The tips on my steady rest are brass. Every time I attempt to use my steady rest, the three plungers eventually cut an unwanted grove in my work piece.

        Harold
        For those having fought for it, Freedom has a flavor the protected will never know.
        Freedom is only one generation away from extinction.

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        • #5
          Oil, or spend a day building tips with ball bearings on them!

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          • #6
            You can also find a bearing to press over the shaft, set your steady rest fingers on the outer race of the bearing, then press it off when you're done machining
            Last edited by lbhsbz; 02-25-2011, 02:18 AM.

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            • #7
              To avoid damage from your steady rest, Make a spider that grabs onto your workpeice with 3 or more set screws, Put padding under each set screw to avoid damage to workpeice.
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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              • #8
                Make a cathead similar to this...



                ... it was made by John Stevenson and he discusses it in the following thread:

                http://bbs.homeshopmachinist.net/showthread.php?t=33552

                .
                Last edited by Mike Burdick; 02-25-2011, 02:52 AM.

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                • #9
                  If you need to work on the end, you need a steady rest. Get the end in the 4-jaw running true. Slide the steady rest up next to the chuck and adjust the fingers, then slide it out to support the end. If you try to adjust it in its final position it will always look as though it is correct but it can be misaligned which will make the work wobble and walk it out of the chuck.

                  Adjust the fingers so they *just* touch, and apply oil. You shouldn't get significant wear on the work.
                  ----------
                  Try to make a living, not a killing. -- Utah Phillips
                  Don't believe everything you know. -- Bumper sticker
                  Everybody is ignorant, only on different subjects. -- Will Rogers
                  There are lots of people who mistake their imagination for their memory. - Josh Billings
                  Law of Logical Argument - Anything is possible if you don't know what you are talking about.
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                  • #10
                    I'd go with the bull nose live center unless you have to work on "face" end of the pipe.
                    Andy

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                    • #11
                      Originally posted by SGW
                      If you need to work on the end, you need a steady rest. Get the end in the 4-jaw running true. Slide the steady rest up next to the chuck and adjust the fingers, then slide it out to support the end. If you try to adjust it in its final position it will always look as though it is correct but it can be misaligned which will make the work wobble and walk it out of the chuck.

                      Adjust the fingers so they *just* touch, and apply oil. You shouldn't get significant wear on the work.
                      Good suggestion. I could see this method working better on smaller diameter stock. One would think, as diameter increased so would the difficulty of sliding the rest near the end (less flex in 2 or 3 inch diameter than say half inch or 1 inch stock. Am I thinking right on this?

                      Harold
                      For those having fought for it, Freedom has a flavor the protected will never know.
                      Freedom is only one generation away from extinction.

                      Comment


                      • #12
                        hwingo, if you have brass tips on your steady rest then put a length of 1" wide emery cloth around the work under the fingers and clamped between the jaws of the steady rest with the smooth side toward the work. Put oil between the emery cloth and the work and keep close attention to the pressure the fingers are applying to the work to keep it centered. You don't want them to get loose or tight and keep the chips out of the area with a piece of cardboard over the work and against the steady rest.

                        This works very well for quick setups. You can also make a sleeve to go over the work or a cat head but all those take a lot of time and care to set up and get centered.
                        It's only ink and paper

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                        • #13
                          I had a similar issue lately and when I got out my new-to-me bull-nose center it turned out to have what appears to be a 1-1/2 morse taper. (I assume it's a different taper standard.)

                          I turned a short tapered plug with a center hole and stuck it in there. Turning a tapered plug meant very little measuring was required.


                          Shrunk on collar by fciron, on Flickr


                          Fixed! by fciron, on Flickr
                          Last edited by fciron; 02-26-2011, 03:24 AM.

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                          • #14
                            Good solution fciron, make sure the face of the plug is running true and you're good to go. You can now true up the od of the piece for a steady. Peter
                            The difficult done right away. the impossible takes a little time.

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                            • #15
                              Thanks!

                              I used my largest center drill when making the plug. Then held it against the live center in the tailstock to guide it into the hole. I could have used a third arm, but everything lined up nicely in the end.

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