What is deep-hole drilling? Methods, common problems and the right machines

Deep-hole drilling usually means drilling holes deeper than about ten times their diameter (L ≥ 10×D). Such holes appear in shafts with full-length oil holes, hydraulic cylinders and many other parts – but standard drills struggle with chip packing, heat and hole run-out.

Why deep holes are difficult

• Chip evacuation: the deeper the hole, the harder chips are to remove; packed chips break tools and spoil the bore.
• Heat and lubrication: ordinary coolant cannot reach a cutting edge that deep.
• Straightness: long tools can deflect, leaving a crooked or off-centre hole.

Common methods

Gun drilling

A single-flute drill with an internal coolant channel: high-pressure coolant flows through the drill to the cutting edge and carries chips back along the outer V-flute. Suited to small and medium holes that need straightness and a good finish.

BTA / STS

Coolant flows in around the drill tube and chips leave through the centre of the hollow tube. Suited to larger holes and high penetration rates.

Ejector system

A double tube carries coolant in and chips out inside the tool itself – useful where a high-pressure BTA seal arrangement is impractical.

What makes a good deep hole

• The right coolant pressure, flow and filtration.
• Guiding the drill at entry with a guide bushing or pilot hole.
• Speeds, feeds and insert grades matched to the material.
• A rigid machine and well-aligned workholding.
• Regular checks of hole size and straightness.

Typical parts

Shafts with full-length oil or centre holes, hollow shafts, hydraulic cylinders, parts for automotive, oil and gas and aerospace (such as landing-gear components) and cooling channels in moulds.

Machines for volume production

For high-volume shafts, multi-axis and multi-spindle deep-hole drilling machines drill several parts or holes at once and fit into automated lines with double-head CNC lathes and grinders. NKE is the official LECN agent in Thailand; LECN offers multi-axis and multi-spindle deep-hole drilling machines for shafts. See LECN machines in Thailand, or send us your drawing and our engineers will recommend a method.