I have been following the thread about tightening hammer handles.
Try an old blacksmiths trick. Place the hammer head down in a can of
common automobile antifreeze. (ethylene glycol). Let it soak for a
few days to a few weeks depending how loose it is. The antifreeze
will not harm the hammer and it swells the wooden handle fibers.
Beware that the antifreeze is poisionus if injested and it has a
sweet taste so pets and children will drink it.