Try using Chair-Loc on the end of the hammer handle where it exits
the top of the hammer head. This liquid is used to tighten joints in
wooden chairs and it works miracles with hammer handles..
You only need to use a drop at the most as it will cause the wood of
the handle to swell, thereby anchoring the handling in the head. If
you use too much, you might run the risk of splitting the head with
the pressure, so I've been told.
After you add the drop of Chair-Loc to the end of the handle, hold
your hammer vertically with the 'grip' end resting on your benchtop
and the hammer head 'up'. Bang the 'grip' end of the handle on the
benchtop, giving it a solid thump. This shifts the hammer head down
a little and anchors it more firmly on the handle. Let the hammer sit
for an hour before using (even more time might be better, but I know
you'll want to be using the hammer). This will secure the head for
long use and the process can be repeated when the handle dries out
in the future (it's wood, so it will shrink and swell again and
Just 'google' Chair-Loc and lots of suppliers will show up. Your
local hardware store might also carry it. Pretty common item.
Hope this helps,