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Tramming a Rotary Table In The Vertical Position

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  • Tramming a Rotary Table In The Vertical Position

    I'm shut down due to weather, so I figured I'd post something that might be of use to somebody I guess.

    A rotary table is a funny thing to set up. You're working in 3 dimensions. X, Y, and Z axis.

    First thing is checking how the base of the table corresponds to the mill table. It should be absolutely square to the table in the Z axis.

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    The mill table is raised, and lowered, to measure any difference between "top" and "bottom". Variances are eliminated with shim stock placed under, either the leading edge of the table, or the trailing edge. Idea is to tilt the table in the direction you need it to go. I prefer using the knee crank with the indicator attached to the mill head. I don't feel that the quill is accurate enough to really get a good measurement. Remember to lock the knee at bottom, and top, of travel. This eliminates any error.

    Next, we need to check our work using the chuck (if you're using a mounted chuck).

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    Chuck a reasonably accurate piece of round stock, and see how it trams out over its length. I like doing this because the workpiece is gonna be clamped in the chuck, and I want to see just how much error the chuck is introducing into the setup. This is a comparative test, not something you want to swear by, unless the results are absolutely out of whack. You're just verifying your original setup that ya did with the indicator.

    Next, we gotta set the tailstock height. This involves a center. Any reasonably accurate center will do.

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    Pop the center in the chuck, then run a test bar between chuck, and tailstock.

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    Adjust the tailstock to achieve equal measurements from side to side, along the top, on your test bar.

    Why use the chuck, instead of the taper in the rotary table? Your work attaches to your chuck, not the ground taper in the rotary table. Chucks, and chuck mounts, have error. You want to take that error into account when you tram. The world isn't perfect, and ya gotta do yer best to iron out the humps. AND...……….remember...…….your workpiece is mounted in the chuck, not the rotary table center. It's the work you need to run true, not an imaginary axis.
    Last edited by farmersamm; 03-23-2020, 04:41 PM.

  • #2
    Now, let's look at the X axis. We need the table to run true to the X, and Y, feed of the milling table.

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    Crank the table away, and towards, you. Measure the difference, and correct it.

    This should also check out when you place the round stock in the chuck for the Z measurements. See the second picture in the first post.

    You've now trued the table to the milling table, AND the mill spindle.

    Next...……...Clamp your workpiece in the chuck.

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    Check runout at the chuck face, and at the end of the workpiece. Correct with a mallet as necessary. Then slide the tailstock into the end of your workpiece. The indicator should not move. If it moves,, adjust the tailstock accordingly...…..sliding it towards, or away, from you. When there's no movement, and the runout at both ends of the piece is identical...…'re about as close as you can get. Remember to check both top, and side, of the workpiece. This covers all 3 dimensions.