counterbore

American  

[koun-ter-bawr, -bohr, koun-ter-bawr, -bohr] / ˈkaʊn tərˌbɔr, -ˌboʊr, ˈkaʊn tərˈbɔr, -ˈboʊr /

noun

1. a tool for enlarging a drilled hole for a portion of its length, as to permit sinking a screw head.

2. the portion of the hole so enlarged.

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verb (used with object)

counterbored, counterboring

1. to enlarge (a drilled hole) along part of the length of the hole by drilling with a bit having a greater diameter.

Other Word Forms

• counterborer noun

Etymology

Origin of counterbore

First recorded in 1605–15; counter- + bore ²

Example Sentences

A counterbore in the arbor hub provides clearance for the hub of the pulley which projects beyond the rim on one side.

From Turning and Boring A specialized treatise for machinists, students in the industrial and engineering schools, and apprentices, on turning and boring methods, etc. by Jones, Franklin D.

For enlarging a hole for a certain distance the counterbore is employed.

From Modern Machine-Shop Practice, Volumes I and II by Rose, Joshua

For counterboring small holes or for facing the metal around their ends, the form of counterbore shown in Fig.

From Modern Machine-Shop Practice, Volumes I and II by Rose, Joshua

If taken off at all it must be pulled, for the dowel-pins, key and counterbore are close fits.

From Steam Turbines A Book of Instruction for the Adjustment and Operation of the Principal Types of this Class of Prime Movers by Collins, Hubert E. (Hubert Edwin)

When the cannon is loaded, a small quantity of powder is placed in the counterbore, and the spark between C and E ignites this and discharges the cannon.

From The Boy Mechanic: Volume 1 700 Things for Boys to Do by Popular Mechanics Co.