Straight flutes and double margins are other design features that can enhance surface finish. Straight flutes minimize the spring effect common in drills with helical flutes, and the double margin aids centering. Although these tools are more expensive than conventional drills, using them isn t always more expensive. For this reason, manufacturers can reduce the cost of making quality holes and, indeed, make them free by suggesting these advanced drills to manufacturing departments that are challenged to achieve good surface finish. If manufacturing is already using them, yet finish problems develop, quality control can shorten the troubleshooting process by offering more feedback than simply informing the machinist that the surface finish is not within specification.
Inspectors can look for various telltale signs to help manufacturing solve the problem.
Although the drill s geometry affects surface finish dramatically, Yakamavich said it can be ignored if manufacturing is using the advanced drills recommended by cutting tool manufacturers for the work material and hole size at hand. Wear, a diagnostics tool Assuming that the tool is the correct one for the job, the first item to check when a finish goes bad is tool wear. In general, wear along the cutting edges of the tool degrades surface finish because it alters the geometry. Advanced drills have as positive a rake and as great a clearance as possible for the given work material to enhance the shearing action that creates smooth finishes. As the edge wears, however, the geometry becomes less positive, leaves a rougher surface, and eventually smears the surface.