three types of gun drilling machine VS accuracy

1. Rotating both part and gun drill is the most accurate process as regards concentricity (center line drift). The part spindle rotates the part counter clockwise with slow RPM (200 – 1,000), while tool spindle rotates the gun drill clockwise with the cutting speed based on gun drill manufacturer recommendation. Part counter rotation can improve center line drift 3-5 times better than the one without it.
2. Rotating part with stationary gun drill is the second accurate process as regards concentricity. It is primarily applicable only to symmetrical part like bar stock can be held in chuck or collet.
3. Rotating gun drill, stationary part is the least accurate process. The process is very common in gun drilling non critical features like water lines on mold, vent relief on heat transfer parts, while part is non symmetrical or large block.