Runout

Tool holder runout directly affects hole quality in deep hole drilling. I have measured the runout difference between collet holders and side-lock holders on dozens of gun drill setups, and the gap is significant enough to dictate which holder I use for each job. A difference of 0.01mm in runout at the holder can become 0.05mm or more at the drill tip. Problem Description Runout at the cutting edge causes the drill to cut unevenly. One side of the drill takes more material than the other, producing an oversized hole and accelerated tool wear. On gun drills, which rely on a single cutting edge and two guide pads, runout pushes one guide pad against the bore wall harder than the other, causing rapid pad wear and poor surface finish. ...

Runout is one of those problems that is easy to ignore because the symptoms look like other issues. A hole comes out 0.03mm oversize and the natural instinct is to check the drill diameter or the bushing clearance. Half the time, the culprit is tool runout. Here is what I have learned about measuring runout, understanding its effects, and controlling it. What Runout Actually Does to the Hole When a gun drill has runout at the tip, the cutting edge orbits around the spindle centerline instead of rotating on-axis. This orbit increases the effective cutting diameter. ...

What Tool Runout Does to Your Holes Tool runout is the amount the drill wobbles off its true center of rotation. A drill that runs true produces a round hole at the nominal diameter. A drill with runout produces an oversized, bell-mouthed, or irregular hole. I have measured the relationship between runout and hole size many times. A runout of 0.02mm at the drill tip produces a hole that is 0.03-0.05mm oversized. The extra material removal wears the tool faster and leaves a poorer surface finish. ...