Definition of counterbore in English:



  • 1A drilled hole that has a flat-bottomed enlargement at its mouth.

    • ‘This is followed by a two-pass drilling operation to produce the counterbore and the bolthole.’
    • ‘In the new design, the holes are formed with a lead-in chamfer to facilitate pushpin insertion and a counterbore formed inside the hole that creates a shoulder to hold the pins in place.’
    • ‘A counterbore surrounds each rivet receiving opening in the flat bottom surface.’
    1. 1.1A drill whose bit has a uniform smaller diameter near the tip, for drilling counterbores in one operation.


  • Drill a counterbore in (an object)

    • ‘If the wood is thicker than three-fourths of an inch, you can either substitute longer screws or counterbore the interior surface of the door or drawer so that the screw head is recessed into the wood.’
    • ‘There are those operations that are strictly drilling operations, but we also use drilling machines to perform other operations such as reaming, tapping, countersinking and counterboring.’
    • ‘Headless press fit bushings offer two advantages: they can be installed flush with the jig plate without counterboring the mounting hole and they can be mounted closer together than headed bushings.’
    • ‘It is an optional tiebar style with mounting holes drilled and counterbored for 1/4 inch SHCS.’
    • ‘When you're faced with the problems of ovality, camber, or drift in drawn or cast tubing, we'll use counterboring to re-size a hole to a controlled dimension.’
    • ‘A tool steel mandrel and durable hardened steel mounting blocks provide positive grip and the 1.5’ feed length is perfect for deep counterboring and additional accessories.’
    • ‘I also counterbored the top holes and plugged them.’
    • ‘Some operations, such as counterboring the mounting holes for the chuck, could have been done more easily using my Grizzly mini-mill, but I wanted to present a plan that would work for lathe owners who have only the stock lathe and a drill press.’
    • ‘The end of the sleeve inside the mount was shortened and counterbored to accommodate the 0.16 NA beam.’
    • ‘After counterboring to (in this case a very thin wall) allow the barrel lens to fit back into the adapter and near the iris the fit is verified in the lathe.’
    • ‘This learning module will show you how to perform four internal machining operations on the engine lathe: drilling, boring, counterboring, and reaming.’