Test Indicator vs Co-Ax Indicator Accuracy ?
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  1. #1
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    Default Test Indicator vs Co-Ax Indicator Accuracy ?

    I've been trying to wrap my head around this question. This comes up when we have one of our CNC lathes that gets bumped or crashed and we are dialing in an ID toolholder to get it back to X zero.

    I can use a coaxial indicator mounted in the chuck and sweep it and it will look fine. When I use a test indicator mounted on a mag base it is still way off. I realize you really have to be careful with spindle droop when using a mag base for this. Anybody have a suggestion what mag base or attachment works best with the least fighting droop?

    My thought is that with the co-ax depending on the length of the attachment and it is different how much you you move X to get the dial to move on it.

    I'm not sure this makes any sense, but are there any thoughts?

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    The shortest stubbiest most rigid mag base you can get your hands on. If you search this forum for dialing in tailstocks you’ll find more than you’d ever want to read regarding indicator sag and how to combat it.

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    Quote Originally Posted by munruh View Post
    I've been trying to wrap my head around this question. This comes up when we have one of our CNC lathes that gets bumped or crashed and we are dialing in an ID toolholder to get it back to X zero.

    I can use a coaxial indicator mounted in the chuck and sweep it and it will look fine. When I use a test indicator mounted on a mag base it is still way off. I realize you really have to be careful with spindle droop when using a mag base for this. Anybody have a suggestion what mag base or attachment works best with the least fighting droop?

    My thought is that with the co-ax depending on the length of the attachment and it is different how much you you move X to get the dial to move on it.

    I'm not sure this makes any sense, but are there any thoughts?
    Ive noticed this also. one reason I believe is that when you hold a coax indicator so the dial doesnt spin just the slightest touch will change it.
    now if you put a rod on it to keep it from spinning if you watch the little u-shaped bracket that rides on the face of the houseing you can see how and why its not accurate. thats why I just dont trust coax indicators.
    That face has to be smooth as heck and not have any run out on the face or the c shaped part that rides on it. another words to many moving parts in a coax.

    I use a inter rapid .0001 indicator and a mirror. locate directly on the pin in a collet machine. in a chuck machine I use a er straight shank and and put the indicator in there. otherwise I will take the time and make a spider with a hole in it to accept the indicator.

    I never used a mag base in a lathe spindle for 30+ years of running and working on lathes because it just isnt going to be exact.
    sure might be faster and and easier. to be honest you will be just as close taking your O.D. tool and cutting the face and eyeballing it.


    There was a german company that made a coax that was extremely accurate it was electronic didn't refresh fast enough but it was nice. came out around 1996. you could touch the body with slight pressure and the needle didn't change. They were pushing close to a grand back then. cant remember the name.

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    Check into a Haimer Centro.

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    Quote Originally Posted by pmack View Post
    Check into a Haimer Centro.
    Aside from rigidity, OP doesn't mention resolution of the Co-Ax versus the test indicator. Co-Ax in .0005/ 3/4" dial is nothing like a .0005 or .0001 in 1-3/4" dial face.

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    I have a Blake which I used often time and felt secure in its accuracy. I just checked on the current price and almost messed my fresh Depends..$400 clams. I know for a fact that I didn't pay anywhere near that, although I bought my many years ago.

    Stuart

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    I have a Blake clone. I use it to get close, then switch to a DTI to get balls on.

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    every dti I have ever used is useless for lathe turret alignment.
    try this as an example of gravity at work on small clock parts.
    mount a dti directly to a solid part in the horizontal plane via a clamp avoid the mag base,touch the needle onto the block and set the dial to "zero"

    now lift it above your head and rotate it upside down... I have found this to show more than 0.1mm of movement

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    I thought you weren't supposed to measure upside down with a dti?

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    Quote Originally Posted by munruh View Post
    I've been trying to wrap my head around this question. This comes up when we have one of our CNC lathes that gets bumped or crashed and we are dialing in an ID toolholder to get it back to X zero.

    I can use a coaxial indicator mounted in the chuck and sweep it and it will look fine. When I use a test indicator mounted on a mag base it is still way off. I realize you really have to be careful with spindle droop when using a mag base for this. Anybody have a suggestion what mag base or attachment works best with the least fighting droop?

    My thought is that with the co-ax depending on the length of the attachment and it is different how much you you move X to get the dial to move on it.

    I'm not sure this makes any sense, but are there any thoughts?
    .
    tram error. that is the center of a short tool tip and be different that the center of a long tool tip. hard to describe. just saying machine alignment often reason you can get different readings even with a rigid setup.
    .
    by the way take indicator and rod setup (same length and type as going to use later) and mount on a solid pipe and zero with indicator at the top and rotate pipe and read indicator at the bottom. this sag amount is what you need to compensate for sag of indicator setup.


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