"Dave Liquorice" wrote in message
ll.co.uk...
On Fri, 2 Jul 2010 05:40:44 -0700 (PDT), Owain wrote:

Half a copper ball-cock ball?

6" copper float about a tenner from BES, 8" also available.

Good bit of lateral thinking, bit big for a the top fo 4" post but

Probably easier to panel-beat an attractive dimpled finish into an
existing hemisphere than try and form a hemisphere from flat sheet.

I agree, I'm no panel beater but just thinking about how a flat sheet
of metal will need to stretch and bend to form a hemisphere is
non-trivial. One might be able to get a half hemisphere without a
skirt fairly easily but a full one which self forms to a skirt would
be much harder.
--
Cheers
Dave.

Just reminded me of our old 'Ericson' tester: basically a metal ball pushed
into sheet metal to test it's ductility. We had stacks of little domed
plates... If you have a decent hydraulic jack or press and a metal ball and
ring to push it through you might be able to cold form your shape. Be bold:
you could even do something like jacking the car up with your plate and a
former between. You could hollow a block of wood and use your fence post
wooden ball, and the jack to push it in. Lots of uses for jacks...

If you are knocking up from scratch, the rim is the bit you are holding.
Finish it last, then cut off the excess with snips (or snips, then finish:
depending on how hard it gets). If memory serves that is...

S