Emco FB2 mill - weird Z position shift

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compact8

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I was checking the tram of my Emco FB2 mill today and found something really puzzling. The mill seems to be unable to hold the Z axis position depsite the fact that both the quill and the Z axis were locked. At first I thought the DTI holder of the DTI itself has got something loose but after further checking, the problem seems to come from the quill. The Z position change is as much as 0.05 mm or 2 thou but the wierd thing is the shift depends on the direction of rotation of the spindle prior to taking measurement. I have tried to move the chuck vertically to see if there is any play but there is none. The small deflection of the DTI is just due to the relatively weak rigidity of the machine.

No related issues was seen in actual use of the machine. The dimension error of the workpiece after machining in the Z-axis direction is within 0.02 mm.

Any thoughts guys ?

 
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Perhaps the flutes of the end mill are different lengths or slightly bent and the indicator pad is being pressed unevenly? Perhaps try it with a regular test indicator and see if you get the same readings.
 
Eddyde said:
Perhaps the flutes of the end mill are different lengths or slightly bent and the indicator pad is being pressed unevenly? Perhaps try it with a regular test indicator and see if you get the same readings.
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I have checked again with a ball-end tool and the result is the same .....

 
I would try another tool holder. Ideally you really need a MT2 test bar to test the spindle . It is hard for me to think that the spindle is bent. Are you the original owner?
 
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