Re: Hobber Work Spindle Runout

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Posted by BillS on March 27, 2018 at 12:51:44:

In Reply to: Re: Hobber Work Spindle Runout posted by Tlueken on March 25, 2018 at 16:13:24:

Okay... Looks like you may have found (part) of the problem. Now that you know where the dead center is with respect to an arbor center, the dead center may have to be "shimmed" or ground to match. I would try shimming first to make sure that bringing the center .015 down and .02 away from operator is correct.

To help, you should put your indicator on the arbor (no workpieces mounted!) and bring the dead center onto the arbor. You should see no deflection; if the dead center is corrected.

Something else to consider: when you mount work pieces, bushings, spacers on the arbor, use the indicator to see if tightening on the "nut" causes any deflection. If there is any piece in the stack that is not face to face parallel, then expect deflection.

If the faces are not parallel, there are ways to change stacking orientation that can minimize deflection.

For instance, finger tighten the nut while rotating the workpieces can usually find a minimum deflection. Also, there are spherically ground arbor nut and washer sets that can be oriented to minimize deflection.

The quickest way is to remove the problem by surface grinding contacting faces of bushings, spaces, workpieces, etc. The nut surface should be trued also, but if the threads are a bit of a sloppy fit, the nut can usually self-align.

Don't expect the dead center to correct deflection - the arbor and tightened workpiece stack can usually overpower the center.

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