With a proven CNC program, machining a head is as easy as bolting it to the fixture and pressing "Start." However, running a new program for the first time requires periodic checks to make sure the cutting speed, spindle rpm, and finish on the port and chamber surfaces are all within established parameters. The order of machining operations can be changed on the fly as well. The maximum amount of material removed in one pass should be limited to 1/4 inch. The step-over distance of the tool path determines the size of the ridges that are usually visible with CNC-ported heads. A 0.080- to 0.100-inch step-over is typically used when roughing in a port, and a 0.020- to 0.030-inch step-over is common on the finishing pass. SAM cut its LS-R heads with an ultra-fine 0.005-inch step-over, which creates a smooth finish almost indistinguishable from a hand-ported head.