Dual-Process BTA & Gun Drilling for Hydraulic Components

Customer Background

The customer is a hydraulic component manufacturer producing plungers, piston rods, and valve spools from round bar stock. These parts carry deep axial bores that form oil passages, pilot holes, and pressure chambers — features whose coaxiality and surface finish directly determine sealing performance and service life in the finished valve or cylinder.

The Challenge

Round-bar hydraulic components present a two-diameter drilling problem that is easy to underestimate:

Two-stage bore geometry. Most parts combine a small pilot or feed hole with a larger working bore opening off it. The two diameters are machined by different methods — gun drilling for the pilot, BTA drilling for the large bore — which historically meant two different machines.

Misalignment across machine transfer. When the pilot is gun-drilled on one machine and the main bore BTA-bored on another, the two holes must share a single centerline. Every re-clamping between machines reintroduces eccentricity, surfacing as stepped shoulders and uneven wall thickness where the bores meet.

Large-bore finish requirements. The main bore often carries pressure against seals. BTA drilling produces the surface finish and straightness that sealing requires, while gun drilling a Ø40mm bore at that diameter is slower and leaves a rougher surface.

Chip accumulation at depth. In bores 400–500mm deep, chips pack into the hole and stall the tool. Reliable chip evacuation is the difference between a stable cycle and repeated drill breakage in high-volume production.

Throughput pressure. High-volume hydraulic components reward parallel processing. A single spindle means one part at a time, and per-part cost stays high for what is fundamentally a repetitive operation.

The Solution

RuidCNC supplied a Vertical Deep Hole Drilling Machine (RD500) — an inverted vertical dual-spindle machine that combines BTA and gun drilling in a single setup:

• BTA + gun drilling on one machine — switch from gun drilling (Ø3–35mm) to BTA drilling (Ø25–50mm) on the same clamping, eliminating machine-to-machine transfer
• Dual spindles — two parts machined simultaneously with 15 kW each, doubling throughput per machine footprint
• Inverted vertical arrangement — upright workpiece orientation lets gravity assist chip evacuation from deep bores
• 10 MPa / 100 L/min coolant — through-tool coolant clears chips reliably from both BTA and gun-drilled holes
• 500mm drilling depth — sized for round-bar components up to Ø155mm OD and 500mm long
• Syntec 21MA-E CNC — precise feed control for both processes, with Siemens or FANUC controllers as options

Key Machine Specifications

Parameter	Specification
Drilling diameter (gun drilling)	Ø3 – Ø35 mm
Drilling diameter (BTA)	Ø25 – Ø50 mm
Max drilling depth	500 mm
Spindles	2 × 15 kW
Workpiece max outer diameter	Ø155 mm
Workpiece max length	500 mm
Coolant pressure	0 – 10 MPa
Coolant flow	100 L/min

Results

Metric	Two-Machine Process	RD500 Dual-Spindle	Improvement
Setups per part	2	1	Eliminated
Machine-to-machine transfer	Required	None	Eliminated
Parts per shift	96	178	85% increase
Pilot-to-bore centerline deviation	±0.06 mm	±0.02 mm	67% better
Main bore surface finish (Ra)	2.4 µm	0.9 µm	63% better
Scrap from re-clamping errors	3.2%	0.6%	81% reduction

Process Validation

The process was validated through:

• Coaxiality inspection of the pilot and main bore on a CMM
• Surface finish measurement along the full main bore length
• Pressure testing of representative finished hydraulic components
• Process capability study (Cpk) on bore diameter across a production batch

Conclusion

The RD500 answers a process-engineering problem — combining BTA and gun drilling — with a machine design that also doubles throughput. By holding the pilot and main bore in one clamping on dual spindles, the customer eliminated transfer misalignment, improved main-bore surface finish for sealing, and increased parts per shift by 85%. For manufacturers of round-bar hydraulic components, the RD500 converts a two-machine, two-setup process into a single, parallel machining step.

Figures are representative of typical applications.