Turning Non-precision Eccentrics in a 3 Jaw Chuck

[mklotz]

Thanks, Rick, for the credits.

The ECCENT program to which Rick refers does indeed calculate the required packing thickness needed to turn a desired eccentric in the 3 jaw. I've never been comfortable with the precarious pinching hold on that packing, though. Rick's scheme removes the need for this loosely secured missile and that's a very good thing.

There is, however, another way to do eccentrics in a 3 jaw that is very safe. The extract below from the text file that accompanies the ECCENT archive describes it...

Imagine a tube bored to be a sliding fit on the parent stock. A slot of sufficient width to pass one of the three-jaw chuck jaws is milled lengthwise in this tube. The parent stock is inserted in the bore and the whole thing clamped in the three-jaw chuck such that one jaw passes through the slot to seat on the parent stock while the other two jaws seat on the circumference of the tube. Obviously the centerline of the parent stock is offset from the lathe spindle axis and turning will produce an eccentric. If we know the OD of the parent stock and the amount of the offset required, it's possible to calculate the OD of the tube needed to produce just that offset when clamped as described above. That's exactly what ECCENTUB does.

The ECCENTUB program is included in the ECCENT archive. If the packing scheme scares you or you don't have a 3 jaw with removable jaws you might want to consider this alternate method.