Cnc lathe alignment mystery
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  1. #1
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    Default Cnc lathe alignment mystery

    Okuma crown. Problems with cutting straight. Had taper, with highs and lows in betwee.

    Technician checked for level, spot on..
    Checked gibs, turret, adjusted headstock to correct taper. .0003 in 7 inches..but has .0015" hump in the middle.. here's the catch.. mag indicator on turret and track along the turned diameter with z axis shows .003"..

    Any ideas welcome


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    The first thing, I would look for is soft foot on the machine base.

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    I wrote a help before, but I hit something and it disappeared. I also thought there might be a loose jack screw in the middle under the cutting area. Also buy or make some ground test bars of at least 1 1/4 and chuck and indicate them in headstock, turret holder and between centers and do some indicating. Or the floor under the machine has some issues. If your not sure the floor is good. Set a precision level on a small surface plate on the floor in front of the machine and zero it. Then move the saddle down the bed and watch the level X and Z. Let us know what happens
    Last edited by Richard King; 03-10-2019 at 03:53 AM.

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    The level was checked at multiple places while moving the saddle along the z axis.

    I was told it was very good.

    We talked about chucking up a ground rod, and checking that but didn't get to that yet. Will try to get at that early this next week.

    The confusing part is what would cause the indicator tracked along a turned shaft show something largely different than what it mics.

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    Your testing a know straight surface. No wondering if it is the ways or bad spindle bearings or bad work holding or dull or loose tooling. One needs to be a detective and not assume anything. So testing a true test bar eliminates some possibilities.

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    I have some questions....

    What size of machine?

    What exactly are the feet of the machine sitting on?

    Hopefully it's a one slab of decent thickness and the feet themselves are actually on some sort of steel plate.

    I wouldn't even bother with a ground rod, until I did the following.

    Grab some 4" OD x 12" stock and turn it in the machine, then measure and correct from there. Then align the rest of the machine to the spindle.

    You can in alignment while not cutting and then be out of alignment when your cutting. That is why I suggested soft foot.....

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    After a great deal of head scratching, the problem was a loose gib. It was supposedly checked. But when machine was torn apart, inspected, and put back together the problem was still there.

    The tech started over at the beginning of alignments, tightened one gib a bit more, and problem was gone..

    Lesson learned..

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