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Thread: Improving import co-axial indicator?

  1. #1
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    Default Improving import co-axial indicator?

    So I recently bought an import co-axial indicator at an auction. It was only after I became the owner of of the indicator that I did some research on how to use it, and how to check for built-in error. This unit has 7 tenths of error. I am considering lapping the high side to reduce the error. I realize that I am likely to generate a somewhat rippled surface but if the end result is less overall error I don't see where I could go wrong. I have several grits of Clover grinding compound at my disposal. See image - the band at the bottom is the zero displacement (no error) zone. Opposite side is Max error of 0.0007. I would like to be able to cut it down to 3 or 4 tenths.

    Your thoughts. I'm into this for a bit under $40 so it's worth it for me to try to improve it but not so much money that I would be scared to destroy it.

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  2. #2
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    Short of taking it to a belt sander, I don't think you could possibly make matters worse. I would first check for some more basic problem, like burrs interfering with the assembly of the various parts. And then I would try just polishing that rough machined surface as a first step. That alone may make a big difference.

    After that I see no problem with lapping it and the pads that ride on it.
    Paul A.

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

  3. #3
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    My real Coax has a 0.0005” offset and the value is written on the dial. I think the “wobble” is intentional, as a dither signal to help you find the minimum and not get into a sticky zone. I would not try to lap your unit. Instead, as you dial in a hole or whatever, work X and Y until the dither is minimized. Then you are on center.


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  4. #4
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    Agreed. You can't get a 'value' of offset from a coax, everything depends on probe length and angle. When you get it down from a swing to a jitter you're there.

  5. #5
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    Quote Originally Posted by chipmaker4130 View Post
    Agreed. You can't get a 'value' of offset from a coax, everything depends on probe length and angle. When you get it down from a swing to a jitter you're there.
    Yup. OP is way overthinking this. I've used a coax indicator for years and the only thing that matters is that
    you tweak the dials till you have the lowest movement--I've never run into a project where this wasn't good
    enough. There was the odd time that I wanted to dial something in a little closer so I ran a DTI around the
    bore. After a few tries at getting it closer I realized that the coax was all I needed...
    Keith
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  6. #6
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    The co-axial indicator is beaut for roughly setting up to find the centre, but as others state here there is need to use a dial indicator to get closer.

    I have it that the co-axial indicator is only ever going to be as good as the collet+spindle or whatever is holding/aligning the head of the unit.

    If the indicator can be held dead set perfect to the spindle then the task the OP is undertaking will, if he does it right, improve the accuracy of the unit.

    A dial indicator does not suffer from the need to hold it "perfect" in the collet. A dial indicator will cycle around "perfect" with the spindle regardless.

    The two devices are complementary. Use co-axial indicator to get it pretty close. Use dial indicator from there to get it "perfect" if needed.

  7. #7
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    Quote Originally Posted by Norman Bain View Post
    ...Use co-axial indicator to get it pretty close. Use dial indicator from there to get it "perfect" if needed...
    The fact of the matter is--and I pointed this out in my previous post--that, in the world of working machinists,
    "perfect" is seldom, if ever, needed. For 99.99% of the time a coax indicator is all you need. In my shop it would
    be a total waste of time to dial something in with a coax indicator and then switch to a DTI to fine tune the setup.
    If I "really" need to be that close I'm going to start and finish with a DTI and not waste my time fiddling with a coax...
    Keith
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  8. #8
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    Quote Originally Posted by LKeithR View Post
    The fact of the matter is--and I pointed this out in my previous post--that, in the world of working machinists,
    "perfect" is seldom, if ever, needed. For 99.99% of the time a coax indicator is all you need. In my shop it would
    be a total waste of time to dial something in with a coax indicator and then switch to a DTI to fine tune the setup.
    If I "really" need to be that close I'm going to start and finish with a DTI and not waste my time fiddling with a coax...
    What would Stefan do? More accurately, what would his OCD allow?
    I need to make or buy a DTI holder for my Bridgeport spindle.
    Here's another thing to consider. I already own a DTI, bet that DTI holder costs a lot less than a coax indicator.

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    Last edited by RB211; 09-01-2019 at 08:17 PM.

  9. #9
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    Quote Originally Posted by RB211 View Post
    What would Stefan do? More accurately, what would his OCD allow?
    He mentioned in a video that he doesn't like coax indicators and prefers to use a DTI.

  10. #10
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    Quote Originally Posted by pinstripe View Post
    He mentioned in a video that he doesn't like coax indicators and prefers to use a DTI.
    Exactly.

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