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  • Indicating a rotary table

    To centre a rotab under a spindle is it better to indicate the hole or mount a indicator, on a mag base, on the perimeter of the table and swing it around the spindle OD. I have always indicated the hole but I tried the other method and there was a .002" TIR.
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

    Southwestern Ontario. Canada

  • #2
    So a .002 difference between the two readings? I'd start by leaving the table steady and try rotating the spindle. There might be a .002 difference between the R8 hole and the outside of the nose of the spindle. Check that to start. See if you can also angle the tip of the gauge to poke up and register off the R8 hole just to be sure. If all that checks out then start checking the table in some manner to see if it is truly concentric to the hole.

    If all that checks out I'd start looking at the rotab and find some way to measure if the table is truly concentric to the hole or if your .002 difference is there. It might mean breaking down the table so you can sweep the ID and OD of the center spindle of the rotab.
    Chilliwack BC, Canada

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    • #3
      Using a pin in the spindle is the fastest,easiest way to locate a RT as you have done Loose nut !
      However my little 6" RT was off ( I have 4 RT's) and I disassembled it and mounted the table backwards in a 4 jaw . then I indicated the radial way surface in and then re-bored the center hole to a snug dowel pin fit. perfect after that
      Rich

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      • #4
        and, if you spin the rotab to indicate the spindle, you can have runout in the rotab itself + runout in the mill

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        • #5
          You need to know which one is concentric with the axis of the RT. Mount both the RT and an indicator stand (magnetic) on the mill table and check the central hole and the OD by rotating the RT. Use whichever one is most true.
          Paul A.
          SE Texas

          Make it fit.
          You can't win and there IS a penalty for trying!

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          • #6
            I've always indicated to the bore, at least that's how I was taught. Thinking about it on my own, I figured the bore is always the "business end" of whatever setup I was doing, and so the bore is the most important thing. Everything else can be as wonky as it wants as long as the bores are true to each other.

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            • #7
              Don't forget to verify tram between the spindle and rotab. If the top of the roab. is not perpendicular to the spindle you are going to get conflicting readings if you sweep the spindle from he rotab.

              Steve

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              • #8
                I just stick the shorter test bar in the MT2 socket in the middle of the Soba 6" table, and the optical sight in the R8 spindle, and get the centre mark concentric, its within 0.001 tir which is good enough for government work. Same with a three jaw chuck, I do up the jaws on the test bar before tightening down to the table.

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                • #9
                  I don't yet have a mill, but I've wondered for the longest time about making a "double ended" bar, with one end to fit the mill spindle, and the other end to fit the center hole in the rotary table. That sounds like a good job to do between dead centers.

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                  • #10
                    Measure the spot that yields the least run out, this will help you overcome your fear.

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                    • #11
                      The reason I'm asking is that I watched a video by Joe Pie on Me-tube and he was stating that it is not uncommon for there to be a discrepancy between the two. I always indicated the hole before so I decided to check it out and there is an difference. There can be a certain amount of collective error.
                      The shortest distance between two points is a circle of infinite diameter.

                      Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                      Southwestern Ontario. Canada

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                      • #12
                        Originally posted by loose nut View Post
                        The reason I'm asking is that I watched a video by Joe Pie on Me-tube and he was stating that it is not uncommon for there to be a discrepancy between the two. I always indicated the hole before so I decided to check it out and there is an difference. There can be a certain amount of collective error.
                        I think I know the video you mean. I always figured it was the hole that matters (especially if its tapered) because thats where the centerline is.

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                        • #13
                          Originally posted by nickel-city-fab View Post
                          I don't yet have a mill, but I've wondered for the longest time about making a "double ended" bar, with one end to fit the mill spindle, and the other end to fit the center hole in the rotary table. That sounds like a good job to do between dead centers.
                          That's exactly how I indicate both of my R/T's.

                          THANX RICH
                          People say I'm getting crankier as I get older. That's not it. I just find I enjoy annoying people a lot more now. Especially younger people!!!

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                          • #14
                            I use a Shars axial indicator. A lot of the stuff I do is flat. So I cross mark it and drill a center hole so that the pilot comes out the other side. In the hole in the rotary table I have a spring loaded 60 deg. center. I place the plate on the center clamp it, and then indicate the hole. I'm usually within a couple of thousands which is good enough for what I do

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                            • #15
                              I always use the tables taper and then rotate the spindle to initially indicate off of - and since my tables already checked out true I know if I rotate the handle the table will be right on the money too, but - I have a chuck that mounts in the center by means of a guided arbor I modified to align it - the arbor is dead nutz on also but the chuck is always off a little, since it's not a 4 jaw I just live with it because it's such a small amount but IF the work is critical I skip using the quick guide arbor alignment tool and take the time to dial in the chuck perfectly for the size work piece it's clamping, so the table's taper is spot on - and so is the workpiece and knowing my table is not running "eccentric" when I turn the handle means all the work comes out perfect (in theory) ...

                              Side note; If your table runs eccentric you should have it well memorized at what degree it maxes out at - perhaps even stamped into the tables surface and then stoned flat...

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