Failing concentricity


Hello all,

I'm new here so please let me know if I should post this in a different area. I am fairly new to machining and I am currently having issues with a concentricity tolerance I must hold. I run a vertical lathe machine that has two operations. In the first operation a rotor is clamped and we do all the ID turning after this the rotor is set on a center table, then a mandrel comes over and picks the rotor from one of the turned IDs and completes all the OD turning.

The issue I am having is when the part is ran on the CMM some (not all) of my concentricities are failing. What I find most confusing is that the same finishing tool is doing all my IDs in operation 1. I am concentric to the diameter I cam clamping on with the mandrel, but failing on all the other ones that are checked.

I have indicated all my axis and played with my feeds a bit to see if anything would change, but no luck. I thought I would ask and see if anyone might have some ideas for what I could try.

Thanks for any help!


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You have the correct forum. I would ask you to attach a sketch of the part and show the diameters that are in/out as well as what you use to clamp, but you will need a minimum of 5 posts before you can attach a document. Can you provide more detail to help us visualize this?


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It sounds like there is a second setup between the ID and OD turning? If so, I would look there. Also, what kind of chucks/workholding are you using? 4 jaw chucks are probably best for this.


So I am familiar with running rotors on a CMM. Multiple areas needed to check concentricity. Usually when running a product like that, Your datum is a center of some sort in which you are trying to compare the concentricity too.

I imagine you have shafts on both ends of your rotor and you need to create a datum or feature to measure too. But you could just have the rotor body.

The best way for this example is to create a cylinder on both ends of the rotor. Whether that's the shafts or rotor body itself. So you should have 2 CYL's. At that point you want to draw line between the 2 cylinders and call that your datum or feature to compare your concentricity too.. Any specific software you are using?
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