I dont want to do it "manually" witht the pen tool, i want perfect curves (semi circles).

If i try to do the curve by hand :
1: it takes too much time
2:it doesnt gets perfect
I know i could do this by creating a circle and then cutting it up to its half, but then the curve is no longer a curve , yes i can then weld them , but that is just a walkaound.
So how do the pro's do it ? whats the right way ?
thanx
(F5), you can specify the angle that the circle begins and ends? Create a circle, set the fill to none, and set the stroke color and width to whatever you like. Now look up to the toolbar. There are two number boxes labeled Start and End. Try changing these values around. You can get half and quarter circles easily, and they are still editable circles. Then just overlap the ends of two circles that are turning different directions.