Fixing worn threads
On so many old movements the threads in the clock plates are so worn as to be of little use, or have been enlarged to a size that is unacceptable: back cock, leaf spring, and bell pillar threads are typical.
My solution for this is to create what I call a nut insert. First drill out the old thread about 1.5mm ? larger than the size of thread that you want to use. Now take a standard hex nut of that size, thread it on to a tap and hold the tap shank in the lathe three-jaw chuck. Let the nut run against the jaws' face, then turn along the nub, leaving a shoulder 1mm thick, and a diameter .003in/.0726mm larger than the drilled hole in the plate. Now press the nut home into the plate with the shoulder on the inside. Finally, run the tap through to resize the thread which will have contracted by virtue of the press fit.
Over the years this has proved to be a very strong and good-looking repair. Use a brass or steel nut, whichever suits.
William Maysey, UK
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