Can someone explain the difference between radius cutting valve seats and angle cutting? I'm familiar with angle cutting but not radius cutting. I'm finding that angle cutting is preferred, particularly on intakes, and some recommendations for radius cutting on the exhaust side. None of the comments were in reference to Y-block heads. 

My heads are being done. The machinist said that he did not think the seats would accommodate 5 angle cuts (15, 30, 45, 60, & 75). However, he said that he could do a radius cut. I'm settling for 3 angles (30, 45, & 60) plus a 30-degree backcut on the intake valves.