Centre Drill Bit Sets

Centre Drill Bit Sets

Centre drills (combined drill and countersinks) are precision tools with two functions: providing the centre location for workpieces turned between lathe centres, and spotting (starting) holes for subsequent twist drills to prevent wandering on curved or inclined metal surfaces. AIMS Industrial stocks centre drill sets in HSS for machine shop, toolroom and general engineering use.

Lathe Centring

When turning a component between centres on a lathe, a 60-degree countersunk centre hole must be drilled in each end of the workpiece to receive the live and dead centres. Centre drills produce this hole accurately in a single operation — the short, stiff body ensures the hole is concentric and on the exact axis of the workpiece. The quality of the centre holes directly determines the accuracy of the subsequent turning work.

Drill Spotting

Centre drills are also used as spotting drills before hole drilling — creating a small, accurately positioned countersink that guides the following twist drill on centre. This is particularly important when drilling on curved surfaces, inclined faces or at hole locations that have been marked with a centre punch. The stiff, short-bodied design resists deflection at start-up, preventing the characteristic wander of a long twist drill beginning in a punch mark alone.

Sizes and Types

Centre drill sets cover BS sizes 1 through 5 (for general engineering) or the equivalent metric range, providing the sizes needed for small and medium turned components. Form A (short) is the standard general-purpose type; form R (radiused) is used where stress concentration at the centre hole must be minimised. For guidance on the right centre drill type for your machining application, contact our team. AIMS Industrial has been supporting Australian workshops since 1988.