Bore

Drill, Bore, Ream, Oh Why!?

Drilling, boring and reaming are distinct hole-making operations. When a hole requires accurate location, roundness, diameter and surface finish, the usual sequence is to drill first, bore second and ream last.

Drilling

Drilling creates the initial hole and removes most of the material quickly. Because a drill may wander, flex or produce a slightly oversized or out-of-round hole, it is commonly used as the roughing operation rather than the final sizing operation for close-tolerance work.

Boring

Boring enlarges and corrects an existing hole with a single-point cutting tool. It can improve the hole’s position, straightness and roundness while establishing a consistent path for the finishing tool. The starting hole must be large enough to admit the boring tool and allow chip evacuation.

Reaming

Reaming removes a small, controlled amount of material to bring a prepared hole to its final diameter and improve its finish. A reamer generally follows the existing hole, so it should not be expected to correct substantial misalignment, taper or out-of-round geometry by itself.

Practical Process

1. Review the blueprint for diameter, depth, tolerance, finish and geometric requirements.
2. Drill the hole undersize while providing suitable coolant and chip evacuation.
3. Bore the hole when its location or geometry must be corrected before finishing.
4. Leave an appropriate and uniform finishing allowance for the reamer.
5. Ream at a suitable speed and feed without dwelling in the hole.
6. Inspect the finished feature with equipment appropriate to its tolerance, such as gauge pins, bore gauges or other calibrated instruments.

The exact stock allowance, tooling and cutting parameters depend on the hole diameter, depth, workpiece material, machine rigidity and tool manufacturer’s recommendations.