OK, I'd suggest you make a simple jig like this out of 9mm MDF:
I'd suggest making it 400x200mm - mark a centreline (100mm in), and a line 100mm from one end. Where they intersect, drill a 30mm hole for the guide bush on your router with a spade or forstner bit. It needs to be a nice fit, with little or no slop.
Once you know the exact radius you need, drill a pivot point for the jig along the centreline. for a 230mm radius, this would be 236mm (230 + 1/4", (half the bit diameter)):
On the underside
of the worktop, mark a line 230mm in from the front edge, and the end. Where these lines intersect is the cenrepoint of your radius. Drill a pivot point the same diameter as in the template. You can then use the drill bit as the pivot:
Place the template into position, and where the centreline on the jig lines up with the mark on the top, place a clamp to act as an end stop:
Repeat at the other side, and check the jig moves freely:
You can then rout the curve, in several passes:
Easier to do than to describe. You can make the jig beforehand, and then set the radius once you're sure of the dimension.
Just remember to work from the underside, and don't drill all the way through!
Hope that helps!!!