The operational performance of gears in terms of smoothness, quietness, wear and life span is largely affected by how gear and pinion teeth make contact. To enhance the operational performance, a crown is often applied to a standard (nominal) gear tooth surface. Regardless of the presence of a crown, all the gears are machined by special types of machine tools, such as gear hobbers and shapers. This paper develops a tooth surface for a spiral bevel gear with a crown so that it can be machined by numerically controlled machine tools. Specifically, we derived: A bi-parametric tooth surface model for a standard spiral bevel gear. 2. A crown model along the spiral curve direction. 3. A crown model along the involute curve direction.The developed algorithm was tested and implemented in a prototype software system called GearCAM. With the GearCAM system, a set of spiral bevel gear and pinion was machined using a 4-axis CNC milling machine to check the validity and effectiveness of the crowning method. Through various verifications, it is shown that the models developed for the standard and crown gears can be used as a means for design and verification of spiral bevel gears.