Guys
I am going to be making a wobble board to help with rehab from my sprained ankle. For those that don't know it is a circular board approximate 2ft in diameter with half a ball stuck to the underside of it. You then stand on the board (half ball side down ) and try to balance on it. 

I'm looking for ideas for something to cut in half to use as the ball bit, ideally about 6 inches in diameter and easy to cut! Or what material could I use to cast something from? Needs to be drillable and easily cut,
Thanks

Something similar used to be available as a toy...

Basically the disk had a hole cut in the centre, which was slightly smaller then the diameter of a pumped up ball, which sat in it.

The ball was inflated whilst halfway through the hole, hence, half the ball was stuck out above and below.

Not exactly what you're after but a thought.

Back in the 80's or 90's there was a toy called a "YOYO ball " or a "LOLO ball" - worth a question on FREECYCLE to see if any one has one it the SHED or ATTIC

So what are you going to do for your broken neck?

I have made a few but the best one I was out of a hockey ball cut in half

Sounds more likely to induce a sprained ankle than help cure one!

I used to be a junior international shot and discuss thrower

Ankle stability was a major worry and I spent a lot of time on it.

Wobble boards and rubber exercise balls are the kings of stability training

I wonder if dog's paws have a "fingerprint" so someone could start manufacturing Personal Dogflaps. (Seeing as you wanted an off topic idea )

Maybe you could make the ball by gluing together off cuts of wood? Use layers and shape it.

You can buy one for £20
Might be easier to make a rocker board, only wood needed
http://www.return2fitness.co.uk/Rehabilitation/Wobble_Boards/rockerboard-50cm

[Edited on 27/7/10 by bmseven]

go to a ships chandlers and get a float for a lobster pot or similar.