This is a bit related to the drilling lead topic but anyway ...
I am replacing bronze keel bolts that were installed 80 years ago using the usual herreshoff Manufacturing Co method: Thread both ends of a bronze rod, drill an undersized hole in the lead then screw one of the treaded ends into the hole. The theory was that the threaded bronze self-taps its way into the lead. The trouble with this method is that it is a bear to get the bronze to unscrew from the lead when the time comes. And, for me, the time has come!
In an operation, the memory of which continues to delight, I used the usual array of simple machines like wedges, levers, and rollers to move the 3500 lbs lead ballast out from under the elevated boat and it now lies alongside the hull with the bronze rods pointing skyward just begging to be removed. Yesterday I tried using locked nuts on the threaded top end to turn the first of the keel bolts out of the ballast but it sheared off at the lower threads 1/2" inch below the surface of the lead. Bugger, that lead is darn sticky (susceptable to spalling, if you prefer). Now my plan is to drill out what remains of the bronze -- anyone know how long the threaded section of the Herreshoff bolts on s-boats were? Then I intend to machine out a pocket that will accomodate a bronze nut, washer, and box wrench head. I need to do this for six bolts so any hints on mortices in lead would be appreciated!