Drilling semi spheres

I'm looking for an "easy" way of "drilling" concave holes (semi spheres) in wood.
They are for decorative purposes, will be various sizes but not greater than half the thickness of the wood (ie 30mm thick <mm radius) and will be individually coloured.
Is there a tool that does this?
If not, I would appreciate ideas on how to go about this
regards
Stuart
www.mckears.com

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You could use a plunge router with radius bits, but the bits aren't going to be cheap or easy to find in the larger sizes.

Stuart McKears wrote:
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Yup a router, with some bits like this:
http://www.axminster.co.uk/recno/3/product-Perform-Round-Nose-Radius-Cutters-22879.htm
If you want a cheap and scabby machine just for this one off job then any of the basic catalogue fooder will do the trick. e.g.:
http://www.screwfix.com/app/sfd/cat/pro.jsp?id ’997&ts2191
If you want a decent one to keep then perhaps something like:
http://www.axminster.co.uk/name/trend+T5/sfile/1/jump/0/product-Trend-T5EK-MK2-Router-19901.htm
Background info on routers can be found here:
http://www.diyfaq.org.uk/powertools/router.htm

wrote:
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Very many thanks to you both.
I thought there might be a router cutters but couldn't find the right terminology.
I'm having a not very bright day.
Thanks again
regards
Stuart
www.mckears.com