For example, drill bits with a smaller chisel and thinner web can be more accurate than old 118-degree drill points. The modern geometry, however, cuts that center portion, shearing the chip. The thinner web at the point allows the drill to bite in right away and cut along the centerline from the start of the drilling process. Because the point doesn t get off to a good start, the tool tries to return to the center while it s drilling. This movement often causes a poor surface finish and creates extra heat, which encourages the work material to weld to the cutting edge and scrape the walls.
Advanced drills have smaller chisels and thinner webs than older drill points.
Rather than pushing the material, modern chisels shear the work at the center, making the tool freer cutting and creating a better surface finish. For cutting stainless steel, drills can deliver cutting fluid through ducts in the tool and protect the cutting edges with coatings and cobalt-enriched surfaces. Sandvik Coromant Co. 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.