Thinning the web is the best place to start correcting the problem, because thinner webs encourage the tool to bite into the work. To take it a step further, put a radius on the corner of the tool for a slow transition to the diameter. Material isn t being removed in as big of bites on the outside, and the cutting edge is actually lengthened quite a bit and spreads out the cutting forces on the corner. Other reasons for the tool to deviate from centerline is misalignment or lack of rigidity in the workpiece, machine tool or both. The result is uneven wear or vibration.
Machinists often can hear a little singing and feel the vibration.
They ll usually see catastrophic failure before surface finish deviations develop, though. If the material moves or the spindle is not rigid, the drill is going to break. Because of the new drills, higher speeds and feeds, and the rising trend to complete a job in one setup, rigidity is more of a factor now than it used to be, especially for carbide tooling. Now we have to hold and support the part in three dimensions to counteract radial forces. Drilling is no longer just a simple operation that you put it in a drill press and poke a hole.