There was already an unused hole in the side of the switchbox that was the perfect size for tapping a 10-32 thread. A length of 8mm diameter rod and a 5/16" cable clamp now provide an adequate spindle lock for what I need to do.
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An Improvement -- SATURDAY, AUGUST 25, 2012
I've added a second cable clamp near the spindle to minimize lash. Here's a view of that with the chuck dismounted.
Much better.
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Addendum -- SATURDAY, NOVEMBER 24, 2012
I just discovered a little glitch. When I went to mount the lathe's four-jaw chuck, the parked spindle lock rod interfered with the jaw nuts on the back of the chuck. I had to remove the cable clamp nearest the spindle, and back the rod well away.
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