Dual-Spindle Gun Drilling Doubles Throughput for Round Rod Center Holes

Customer Background

The customer is a manufacturer of cylindrical components — pump shafts, actuator rods, and precision bar stock — that require a straight center hole drilled along the full axis of round workpieces. The center hole is a functional feature: it carries hydraulic fluid, accommodates a pull rod, or serves as the reference axis for subsequent machining.

The Challenge

Drilling center holes in round rod is deceptively simple — the geometry is one straight hole down the middle — but it fails in very specific ways at production scale:

Concentricity is everything. A center hole that wanders off the rod’s axis produces uneven wall thickness, which causes bending during heat treatment and misalignment in final assembly. Holding the hole concentric to the bar’s true axis is the dominant quality criterion.

High-volume, single-op parts. Round rod drilling is a high-quantity application — thousands of rods per month, each needing one hole. Because the operation is simple, production economics depend almost entirely on cycle time per part.

Long aspect ratio. Center holes in 1-meter rods at Ø3–25mm represent depth-to-diameter ratios up to 333:1 for the smallest diameters. Tool deflection and chip evacuation are the limiting factors.

Drill starting wander. When a gun drill enters a round bar, the drill point can wander before fully engaging, causing the hole to start off-center. Preventing entry wander is critical for concentric start holes.

Material variability. Rods arrive in batches of different alloys and hardnesses — from mild steel to hardened tool steel — requiring parameter adjustment that must not slow down the production line.

The Solution

RuidCNC supplied a Round Rod Deep Hole Drilling Machine (RD1000-2S) configured for round rod center hole production:

• Dual spindles — two spindles drill two rods simultaneously, doubling productivity per machine footprint
• Sub-spindle counter rotation — the rod rotates in the opposite direction to the drill, canceling relative runout and delivering excellent concentricity and surface finish
• Siemens Sinumerik 828D CNC — precise programmable control with fast parameter switching between rod materials and sizes
• Customizable drilling range — Ø3–25mm and up to 1,000mm depth, configurable for specific rod applications
• Automatic cycle programming — pre-set drilling cycles for different rod types, reducing changeover time between batches
• Round rod workholding — V-block and tailstock system that clamps the bar on its true axis for accurate center drilling

Key Machine Specifications

Parameter	Specification
Spindle quantity	2
Drilling range	Ø3 – Ø25 mm (customizable)
Max drilling depth	1,000 mm (customizable)
Spindle motor power	11 kW (Siemens)
CNC controller	Siemens Sinumerik 828D
Rotation mode	Workpiece counter-rotation

Results

Metric	Single-Spindle Process	RD1000-2S	Improvement
Parts per hour	18	34	89% increase
Cycle time per rod (Ø10mm × 800mm)	3.2 minutes	1.7 minutes	47% reduction
Hole concentricity	±0.15 mm	±0.06 mm	60% better
Entry wander (start deviation)	0.20 mm	0.08 mm	60% reduction
Surface finish (Ra)	1.5 µm	0.7 µm	53% better
Scrap rate	3.8%	0.6%	84% reduction

Process Validation

The process was validated through:

• Concentricity measurement on a CMM for a full batch of rods
• Cut-section inspection of sample rods to verify wall-thickness uniformity
• Surface roughness measurement along the full hole length
• Process capability study (Cpk) on hole diameter over 100 consecutive parts

Conclusion

The RD1000-2S demonstrates that high-volume round rod drilling is won on two fronts: parallel spindles to double throughput, and sub-spindle counter rotation to guarantee concentricity. The machine increased parts per hour by 89% while improving hole concentricity by 60%, and the Siemens 828D controller kept changeover time low across mixed rod materials. For cylindrical component makers, the RD1000-2S converts a simple operation into a low-cost, high-consistency production step.

Figures are representative of typical applications.