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Holding 6" heavy disc on lathe

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  • Holding 6" heavy disc on lathe

    I would like to run this by you folks before doing it.

    I have plasma cut a 6" diameter disc out of 1/2" steel. I would like to clean up the edges and face the side that will be visible but need to find a way to hold it. My thought was to face the head of a 3/4" bolt then weld it to the part. The bolt would then be held in the chuck. The bolt has a decent length of non threaded section to grip. The disc is mystery metal but I would call it mild steel since it seems easy to work with. The bolt I have is grade 5. The side of the part I would be welding to will be hidden so it doesn't matter that removing the bolt will leave a scar.

    Yes/No? Thank you.

  • #2
    what size chuck do you have? if welding a stub, instead of a bolt, make something large dia - ie 3" pipe with a few stitches, it'll be more solid. Its a tough cut, plasma cut edges can be very tough, can take the end of hss in a rev ....and being intermittent its hard on carbide. A thought would be carbide endmill and a rotary table with enough of cut to get under the out layer. no need for welding, use three clamps and leapfrog around them - move them as required, then face in the lathe.
    .

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    • #3
      I like to use a disc sander to smooth up the edges of a rough cut. That is usually faster and easier than using the lathe. Unless of course you need it really accurate. Mike

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      • #4
        Hi Les

        The disk will wobble if just welded to the head of a bolt. What you need is some way to hold it against your face plate.

        My suggestion is to weld a nut to the centre of your disk and use a length of threaded rod through your lathe headstock spindle to hold the disk firmly against your face plate.
        Another and maybe better way would be to weld three or more studs to the disk and use those to bolt the disk to the face plate.

        As already suggested remove the hard cut edge by grinding before mounting on your lathe.
        Last edited by The Artful Bodger; 11-27-2015, 01:58 PM.

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        • #5
          Les,

          Can you just hold the disk by 1/3 of it's thickness, skim the outer diameter that's sticking out, then reverse it, skim the rest and then skim the face? Some kind of parallels on the chuck jaws will help to hold the disk flat when you're tightening the jaws.

          Ian
          All of the gear, no idea...

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          • #6
            I have trimmed up 11-in disks in an 11-in lathe by tacking on four nuts and grabbing in a big 4-jaw with jaws reversed. Easy-peasy.
            Last edited by rklopp; 11-27-2015, 08:38 PM.

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            • #7
              Originally posted by rklopp View Post
              I have trimmed up 11-in disks in an 11-in lathe by tacking on four nuts ant grabbing in a big 4-jaw with jaws reversed. Easy-peasy.
              I like that idea.
              .

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              • #8
                Put a center hole in the side that will not be visible, use a center in the tailstock to press it against the chuck jaws, clean up the edge to spec, flip it over and grab it by the edge to face it. I think its called "pressure turning" it worked for me in almost the exact situation.

                Last edited by R.Bolte.Jr; 11-27-2015, 03:11 PM.
                "Never bring a caliper to a mic fight"

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                • #9
                  Yeah, my original plan was a pipe but I'm concerned the pipe scraps I have around might be iron and not take the weld well. I posted about the bolt because I had reservations. Thanks for the feedback, I will explore the ideas mentioned.

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                  • #10
                    Face a piece of pipe,tube,round stock.


                    Center and weld three places.


                    Turn and face.


                    Grind welds off.


                    Just did this piece of 1/2" x 5"

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                    • #11
                      That's what my initial plan was but how do i tell if the pipe I have is suitable? I think I read that black iron pipe may not weld well. The pipe I have is short with no markings and has an internal raised seam.

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                      • #12
                        If it has a weld seam it should be steel.

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                        • #13
                          Originally posted by SirLesPatterson View Post
                          Yeah, my original plan was a pipe but I'm concerned the pipe scraps I have around might be iron and not take the weld well.
                          Black iron pipe is steel. Or are you thinking of something else?

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                          • #14
                            The bigger the pipe, the better, as long as you can grip it in the chuck. Less chance of harmonics, vibration as in surfacing brake rotors.

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                            • #15
                              Originally posted by SirLesPatterson View Post
                              That's what my initial plan was but how do i tell if the pipe I have is suitable? I think I read that black iron pipe may not weld well. The pipe I have is short with no markings and has an internal raised seam.
                              How do you think the Indians or the Arabs (UAE), closed up the seam after rolling the strip into a cylinder? Some sort of majik?

                              Quite possibly SMAW. Prep the two pieces to be joined, tack it in a couple of places and see if you can break the tack welds.

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