Micro Gun Drilling Solution for Titanium Orthopedic Bone Screws

Customer Background

The customer is an established orthopedic implant manufacturer producing cannulated bone screws for trauma and spinal surgery applications. Cannulated screws — screws with a hollow center that allows insertion over a guide wire — require extremely precise micro-drilling through the entire length of the screw.

The Challenge

Drilling cannulated holes in titanium bone screws presents some of the most demanding micro-machining challenges in medical device manufacturing:

High aspect ratio. Bone screws require a through-hole of Ø1.5mm with a length of 80–120mm — within the Ø0.9–3mm range and 150mm depth limit of the machine — representing a depth-to-diameter ratio approaching 80:1. At this aspect ratio, tool deflection and chip evacuation become critical.

Titanium machinability. Ti-6Al-4V ELI (Extra Low Interstitials) is the standard material for implant-grade bone screws. Its low thermal conductivity concentrates cutting heat at the drill tip, while its work-hardening behavior means any interruption in feed can cause immediate tool breakage.

Micro-drill fragility. At Ø1.5mm, the gun drill is extremely delicate. Standard micro-drills were lasting only 5–7 holes before breaking — an unacceptable failure rate for production.

Surface integrity. The cannulated hole surface must be free of burrs, cracks, and contamination. Any defect could compromise the screw’s fatigue life or serve as a corrosion initiation site.

Straightness tolerance. The guide wire hole must remain within 0.02mm of the screw’s center axis over the full length. Deviation can cause the screw to track incorrectly during surgical insertion.

Handling small, fragile parts. Screws are delicate and difficult to load consistently; handling variation damages parts and breaks drills.

The Solution

RuidCNC supplied the Medical Components CNC Deep Hole Gun Drilling Machine (RD150-C2) configured for medical cannulation:

• Dual high-speed spindles at 24,000 rpm — two screws drilled in parallel with ≤0.002mm runout, keeping the cannulation stable through high aspect-ratio bores
• Controlled deep-hole feed program — a gun drilling cycle tuned for implant-grade titanium that maintains straightness over the full 80–120mm screw length
• 6-axis robotic arm part handling — automated loading and unloading of delicate screws, consistent positioning, and reduced handling damage
• Sub-micron carbide tooling — gun drills with sub-micron grain carbide substrate and polished flute surfaces, selected for the Ø1.5mm bore in Ti-6Al-4V ELI
• In-process monitoring — real-time spindle load monitoring with automatic feed hold on load spikes to prevent tool breakage

Key Machine Specifications

Parameter	Specification
Drilling diameter	Ø0.9 – Ø3 mm
Max drilling depth	150 mm
Spindle configuration	2 (electric)
Spindle speed	24,000 rpm
Spindle runout	≤0.002 mm
Part handling	6-axis robotic arm
Straightness	≤0.01 mm per 100mm depth

Results

Metric	Previous Process	RD150-C2	Improvement
Tool life (holes per drill)	5–7	120+	17× longer
Cycle time per part	4.5 minutes	2.3 minutes	49% faster
Straightness over 100mm	±0.03 mm	±0.01 mm	67% better
Scrap rate	12%	1.5%	87% reduction
Surface finish (Ra)	1.2 µm	0.6 µm	50% better
Monthly output	2,800	5,000	79% increase

Process Validation

The manufacturing process was validated per FDA requirements with:

• IQ/OQ/PQ documentation
• Full dimensional inspection per ASTM F543 (Standard Specification for Metallic Medical Bone Screws)
• Mechanical testing including torsional strength and drive system compatibility
• Surface integrity analysis per ASTM F86

Conclusion

The RD150-C2 demonstrates that specialized machine design, combined with dual high-speed spindles, robotic part handling, and process monitoring, can overcome the challenges of medical-grade titanium cannulation. With two parts drilled in parallel at 24,000 rpm and automated loading, the customer more than doubled production output while dramatically reducing scrap and tooling costs.

Figures are representative of typical applications.