CNC Boring

Large bores.
Precision concentric.
±0.005 mm.

CNC boring produces large-diameter holes with precision tolerances beyond drilling capability. Jig boring for precision-positioned holes. Line boring for concentric multi-bearing alignment. Standard CNC boring for hydraulic cylinders and large bearing seats.

CNC Boring Quote Deep hole drilling

50 mm+ diameter ±0.005 mm Line bore alignment Any depth

01 · What it is

How CNC Boring works.

CNC boring enlarges a pre-drilled hole to precise dimensions using a single-point cutting tool on a boring head. Unlike drilling (which creates new holes with a multi-point twist drill), boring removes material from the sides of an existing hole, producing very accurate diameters, excellent roundness, and precise positioning.

Standard CNC boring handles common precision bores — typically 50 mm to 300 mm diameter. For specialty applications: jig boring uses extremely precise machines for position-critical bores (tolerance ±0.005 mm on hole centers). Line boring uses a long boring bar spanning multiple bearing housings to machine them all concentrically in one pass — essential for engine blocks and long shaft assemblies.

Boring is the standard finishing operation for hydraulic cylinder bores, engine cylinder walls, large bearing seats, and any bore too large for reaming to handle. Often combined with honing for final surface finish on hydraulic and sealing applications.

02 · Specifications

Capability specs.

50–500 mm

Diameter range

Standard boring range. Larger bores via specialty boring equipment

±0.005 mm

Tolerance

Precision boring tolerance. ±0.01 mm typical standard production

Ra 0.8 µm

Surface finish

Single-pass finish. Better than drilling (Ra 3.2 µm)

Any depth

Depth capability

Boring depth limited by boring bar length, not fundamentally limited

0.05 mm

Position tolerance (jig bore)

Precision jig boring position accuracy for critical features

Concentric

Line bore

Multiple bores machined in single pass maintain concentric alignment

Cycle time

Moderate

Slower than drilling but faster than reaming for large holes

Any ductile

Material compatibility

Standard ductile metals. Hardened materials may require grinding

03 · Applications

Where CNC Boring excels.

Hydraulic cylinder bores

Precision bore for hydraulic cylinders — diameter tolerance for seal performance

Engine blocks

Engine cylinder walls — precise diameter, straight bore, correct finish for rings

Large bearing seats

Bearing bores above 50 mm diameter where reaming is impractical

Line bored bearing housings

Engine camshaft bearings, transmission gear bearings — concentric alignment

Pump bodies

Pump impeller and volute bores — precision dimensions for flow performance

Mill spindle housings

Machine tool spindle bearing bores — extreme concentric and dimensional accuracy

Crankcase bores

Engine crankcase main bearing bores — line bored for shaft alignment

Jig plate features

Precision jig and fixture bores — positioning accuracy for tooling

Large-port manifolds

Aerospace and hydraulic manifolds with large fluid ports

04 · When not to use it

Not suitable for:

Every process has its limits. Being honest about where CNC Boring isn\'t the right answer saves time and money.

Small diameter holes (< 25 mm) — reaming faster and cheaper
Very rough tolerance bores (±0.1 mm) — drilling alone adequate, cheaper
Hardened materials (>45 HRC) — grinding or honing preferred
Bores requiring tighter than ±0.005 mm — grinding or honing
Bores with asymmetric features — milling operations preferred

FAQ

CNC Boring questions.

Diameter above 50 mm (reamers become expensive and unwieldy above this size). Position-critical bores where drift matters (drilling wanders slightly, boring corrects). Roundness-critical applications (boring achieves better roundness than drilling). Bores where dimensions change multiple times during development (boring can adjust to any diameter; reamers are fixed-size).

Machining multiple bearing bores in a single straight-line pass with a long boring bar. Essential for engine crankshaft bearings, camshaft bearings, transmission gear shafts. The bar spans all bore locations, ensuring they're perfectly concentric (within ±0.01 mm). Cannot be achieved by boring each bore independently — individual errors would compound to unacceptable misalignment.

Standard CNC boring: ±0.01 mm position tolerance, adequate for most precision applications. Jig boring: dedicated ultra-precision boring machine with lead screw accuracy of ±0.002 mm, temperature-controlled environment, specialized for position-critical bores. Used for: injection mold plates, precision tooling, aerospace tooling plates where bore positions must be within 0.005 mm of specified location.

Boring produces excellent roundness — typically 0.005 mm on standard production. For critical cylindricity (round both in cross-section and along length), boring with rigid boring bar setup + cylindrical grinding for finish is the path. Hydraulic cylinder bores often boring + honing for optimal combination of dimensions and surface finish.

Boring takes longer than drilling per inch of depth. Boring cycle time: 100–500 mm/min feed rate. Drilling: 500–1500 mm/min. For shallow holes, drill is faster; for deep holes or precision, boring is required regardless of time. Boring cost is justified by accuracy, not speed.

Our line boring capacity: up to 2 m span across multiple bearing houses, bore diameter 50–300 mm. Larger via specialty partners. For line bored engine blocks, crankcases, and multi-bearing assemblies, plan 7–14 day lead time including setup, boring cycle, and inspection. Line boring is a specialty operation — setup time is significant but production quality is exceptional.