Boring: A Machining Process

Boring is a machining process performed to enlarge the diameter of an existing hole. In traditional shops the process is typically performed using a mill or a lathe. For large production runs or for projects that have unique requirements other specialized machines may be utilized. There are several types which include: line boring, tunnel boring, horizontal boring, directional boring, cylinder boring, jig boring, portable boring and vertical boring among others.

At a basic level boring achieves three things:

  1. It brings the hole to proper size and finish. While size is determined by the characteristics of the boring tool itself – the required finish requires the right blend of feed, speed and nose radius.
  2. It straightens the original drilled or cored hole. This corrects defects in castings or drilled holes that have wandered off center.
  3. It makes the hole concentric with the outside diameter which is being held in the chuck, fixture or other work holding device.

Horizontal Boring Machines

A horizontal boring machine is a specially constructed machine typically used to horizontally bore large workpieces. A fairly versatile piece of equipment, it can bore, drill, ream, counter-bore, tap holes and face a part.

Vertical Boring Machines

Imagine a lathe turned on end with is headstock resting on the floor. Very large parts may be bored, cut and contoured utilizing this equipment. For example, part sizes may range from 24” to 120” or more in diameter. The diameter of the part to be machined is limited by the diameter of the machines work table.

Jig Boring

Jig boring is used for holes that typically have very tight diameter and total run-out tolerances. As with the other methods of boring, a pre-existing hole is required in the part – the closer to tolerance the better. Once achieved the part is moved to the jig boring machine to achieve highly accurate hole sizes with very low run-out. It can also maintain high accuracy between multiple holes and surfaces. Tolerances can be held readily within ±.005 mm (±0.0002 inches).

Conventional Horizontal Boring on a Lathe

In the traditional sense, horizontal boring is a machining operation typically performed on a lathe that increases the diameter of an existing hole. The existing hole may have been created in a variety of ways depending upon the type of part or stock utilized. For instance in solid materials, the original hole is made typically with a drill. If the part is a casting or a forging then the hole to be enlarged is often a cored hole.

On a conventional lathe horizontal boring is performed on the Z axis or in line with the center of the lathe tailstock. To achieve alignment sometimes a faceplate or fixture is used so that the hole is properly aligned with the boring bar.

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