Wobbly work piece in the lathe's chuck

Hi Pcmaker, Guys,

A little bit horses for courses with expanding mandrels ! The type I described is a simple home brew way of making one to do a particular job, and for simple tubes works very well, but it is not a precision item. You can buy or make expanding mandrels that are far more precise, which essentially are two tapers pressed together, one inside the other, to expand and grip the work.

For instance, I made a mandrel handle to fit inside the bore of my lathe spindle, it works by expanding the end, by tightening a nut on the exposed end it pulls a cone into a split tube. This causes it to grip the inside of the bore.

Actually a great tool for tapping holes using the lathe.
 
P. Waller said:
As an example I turn 1 or 2 of these parts per year, so far fortune has shined on me this year but there are still 4 months to go (-:
The diameters on each end have a concentricity call out of .005", I am quite sure that I have never achieved this but they always worked in service and have never been tagged.
It is a cam with a 3/8" offset held by bearings on each end and one end accepts a keyed drive component, either gears or belts, I have no idea what it does.
Click to expand...
Sweet!
 
As stated above, concentricity is the measurement between the centers of two features on a part, Total Indicated Runout or Total Indicator Reading (TIR) or Full Indicator Movement (FIM) is the measurement of how far off axis the centerline of your part is to the rotation axis of the lathe or mill spindle. On a perfectly round part, it is double the distance which the axes of the part and the spindle are in error. TIR is influenced by the roundness of your part, as well as the quality of your centers (if your part has drilled centers).
 
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