Multispindle Deep Hole Drilling: High-Volume Simultaneous

Multispindle deep hole drilling machines multiply production throughput by running two or more drills simultaneously — either drilling multiple holes in the same workpiece or drilling identical holes in multiple parts at once. A 6-spindle machine does not simply drill six times faster than a single-spindle; it can reduce overall production cost by 70–80% when labour, floor space, and capital utilisation are included in the calculation. However, the coolant distribution, chip evacuation, and spindle control systems must be designed for simultaneous operation.

Overview ​

Multispindle deep hole drilling machines are purpose-built production systems that range from simple dual-spindle configurations to complex 12-spindle machines with independent CNC control of each axis.

The productivity gain is not linear with spindle count because of auxiliary time (loading, unloading, tool change) that is shared across spindles:

The practical gain is lower because of:

• Reduced feed rate when spindles are closely spaced (chip interference risk)
• Coolant pressure drop when all spindles are active
• Shared auxiliary time that does not scale with spindle count

Machine Configurations ​

By Spindle Arrangement ​

By Drilling Method ​

Independent Spindle Control ​

The most important technical feature in modern multispindle deep hole drilling machines is independent spindle control. Unlike conventional multi-spindle drill heads where all spindles are mechanically linked and must start and stop together, modern CNC-controlled machines allow each spindle to operate independently.

Benefits of Independent Control ​

• Individual engagement — spindles can be engaged or disengaged per cycle. This is critical when drilling near workpiece edges where the first hole must complete before the adjacent spindle can start
• Mixed hole sizes — different diameter drills in different spindles
• Different depths — each spindle can drill to a different depth
• Tool breakage protection — one spindle can retract if it detects a problem while others continue
• Staggered entry — spindles can start at slightly different times to reduce peak coolant demand

TARUS DHMS System ​

The TARUS DHMS series exemplifies advanced independent control. Each spindle has its own:

• CNC servo feed axis
• Bushing nose piece with independent engagement
• Coolant flow control
• Tool life management tracking individual drill usage

This design solves the "edge-of-plate" problem common in tube sheet drilling: the outermost holes are near the plate edge where the workpiece is unsupported. With independent control, the machine can drill edge holes first (at reduced feed), then move inward, avoiding the distortion that would occur if all spindles drilled simultaneously.

Coolant Distribution ​

Simultaneous operation of multiple spindles places high demands on the coolant system. Each drill requires coolant at the correct pressure and flow rate, and the total demand scales with the number of active spindles.

System Requirements ​

(Example values for BTA drilling at 40 mm diameter, 30 bar coolant pressure.)

Flow Balancing ​

Coolant distribution to multiple spindles requires:

• Individual flow control valves per spindle to balance delivery
• Pressure-compensated pumps to maintain setpoint regardless of the number of active spindles
• Accumulator tanks to absorb pressure spikes when spindles engage or disengage
• Filtration system rated for total flow — a 6-spindle machine at 1,000 L/min requires a filtration system sized for 1,000 L/min, not 200 L/min per spindle (because all spindles return coolant simultaneously)

Chip Evacuation ​

In multispindle deep hole drilling, chip evacuation from each hole is independent, but the chip handling system (conveyors, filtration, coolant tanks) must be sized for the combined output.

For gun drilling, each drill's chips exit through its own V-groove flute and are carried by the coolant stream back to a common filtration system. For BTA, each drill's chips exit through the internal bore of its respective drill tube.

Practical consideration: When spindles are closely spaced (centre distance < 3× drill diameter), the chip streams from adjacent drills can interfere. This is managed by:

• Staggering drill start times so one drill is deeper than the adjacent drill
• Using chip-breaking drill geometries that produce shorter chips
• Increasing coolant flow slightly above the calculated requirement for each spindle

Leading Manufacturers and Machine Series ​

Mollart / Bourn & Koch ​

Drillsprint MD Series:

• Up to 8 spindles
• Depths up to 3,000 mm
• Diameters up to 50 mm
• Single-axis CNC (all spindles feed together)
• Fanuc control with dedicated gun drilling HMI
• Automation-ready (auto loading, auto whip guides)

Omnisprint LD2-750 Series:

• 2 spindles (standard), up to 6 available
• 3-axis knee-type design for off-centre holes
• Max diameter: 16 mm (twin-spindle), 22 mm (single-spindle)
• Max depth: 750 mm (1,000 mm optional)
• Ideal for transmission shafts, medical, aerospace

TARUS — DHMS Series ​

• 2 to 5 independently CNC-controlled spindles
• Designed for tube sheets and heat exchangers
• Individual feed and bushing engagement per spindle
• Sophisticated tool life management
• Adjustable spindle pitch

DTI — HMDD Series ​

• 3 horizontal spindles
• Supports BTA, gun drilling (ELB), and standard drilling/threading in one machine
• Max diameter: 81 mm
• Coolant: 800 L/min at 110 bar
• Hydrostatic guides, cast iron construction
• Target industries: energy, chemical, heat exchangers

Tibo Tiefbohrtechnik ​

• Single to 12 spindles
• Gun drilling (2–400 mm) and BTA (18–250 mm solid)
• Drilling depths up to 12,000 mm
• Modular design with ability to shut down individual spindles
• German engineering, custom configurations

Kolb — HTB and MPN Series ​

• HTB: 1–3 spindles horizontal
• MPN: 8–12 spindles vertical floor-type
• Supports both gun and BTA methods
• Individual spindle drives and feed
• Adjustable spindle spacing

Application Examples ​

Heat Exchanger Tube Sheets ​

Heat exchanger tube sheets require hundreds of holes drilled in a precise grid pattern. A multispindle deep hole drilling machine reduces cycle time from days to hours.

Typical parameters:

• Plate material: SA516 Gr70 carbon steel, stainless steel, or titanium
• Hole diameter: 10–50 mm
• Plate thickness: 50–500 mm
• Hole count: 100–5,000 per sheet
• Machine: TARUS DHMS 5-spindle or DTI HMDD 3-spindle
• Method: Gun drilling or BTA depending on diameter

Productivity comparison (hypothetical 250 mm thick, 1,000 holes, 25 mm diameter):

Transmission Shafts ​

Automotive and commercial vehicle transmission shafts typically require a centre oil hole and several cross-holes.

Typical parameters:

• Material: 4140, 8620, or 20MnCr5
• Centre hole diameter: 6–20 mm
• Centre hole depth: 200–800 mm
• Machine: Mollart Omnisprint or Drillsprint MD
• Method: Gun drilling with counter-rotation

Productivity comparison:

Fuel Injection Components ​

Fuel injector bodies require small-diameter deep holes (2–5 mm, 50–200 mm depth) in high volumes.

• Machine: Kolb MPN 12-spindle vertical or TBT multi-spindle
• Typical cycle time reduction: 8–10× vs single-spindle
• Automation: robotic load/unload integrated with machine cycle

Productivity Analysis ​

Total Cost per Hole ​

For a production run of 100,000 holes in a mid-volume application:

The breakeven volume between a single-spindle and a 4-spindle machine depends on capital cost difference and labour savings, but typically falls between 50,000 and 200,000 holes per year.

Breakeven Calculation Example ​

At 100,000 holes/year, the single-spindle is still lower total cost. The breakeven is approximately 180,000 holes/year for this example.

Note: The breakeven volume decreases as labour costs rise and increases as capital costs rise. Each application requires a specific analysis including floor space, maintenance, and setup time.

Process Planning for Multispindle Drilling ​

Setup Considerations ​

1. Spindle pitch adjustment — adjustable-pitch machines require setup time when changing between hole patterns
2. Drill length matching — all drills in a multispindle setup should have similar lengths to ensure consistent peck depths
3. Coolant distribution verification — verify flow balance across spindles at the start of each production run
4. Test cycle — drill a test part and inspect all holes before production release

Operational Practices ​

• Staggered start — start inner spindles first, outer spindles delayed by 5–10 seconds to reduce peak coolant demand
• Sequential tool change — change drills one spindle at a time to maintain production continuity
• Individual torque monitoring — monitor torque per spindle; a torque spike on one spindle should retract only that spindle
• Broken tool detection — each spindle should have independent broken tool detection to stop only the affected spindle

Summary ​

FAQ ​

What is the maximum number of spindles on a deep hole drilling machine? ​

Production multispindle deep hole drilling machines are available with up to 12 spindles (Tibo, Kolb MPN series). Some custom-built machines have been delivered with more spindles for specific applications. The practical limit is determined by available floor space, coolant system capacity, and the workpiece size.

How much faster is a multi-spindle gun drill than a single-spindle? ​

A 4-spindle machine typically achieves 3.0–3.6× the throughput of a single-spindle (not 4×) due to shared auxiliary time. An 8-spindle machine achieves approximately 5–6×. The productivity gain per additional spindle decreases as spindle count increases.

Can different hole diameters be drilled simultaneously on a multispindle machine? ​

Yes, if the machine has independent spindle control. Each spindle can hold a different diameter drill and feed at a different rate. Machines with ganged (mechanically linked) spindles cannot run different diameters. Independent control is available on TARUS DHMS, Nagel/TBT, and high-end Mollart configurations.

What is the edge-of-plate problem in multispindle drilling? ​

The edge-of-plate problem occurs when drilling holes near the edge of a workpiece. The unsupported workpiece edge can deflect under the cutting force, causing hole misalignment. With independent spindle control, edge holes are drilled first (with reduced feed rate if needed), then the machine moves inward — avoiding the deflection that would occur if all spindles drilled simultaneously.

What coolant pressure is needed for multispindle BTA drilling? ​

BTA multispindle systems typically operate at 10–50 bar per spindle, with total flow scaled by the number of active spindles. The coolant pump system must be sized for the maximum simultaneous flow, not the per-spindle average. Pressure-compensated pumps maintain setpoint regardless of how many spindles are active.

Are multispindle deep hole drilling machines suitable for small batch production? ​

Generally no. Multispindle machines are designed for high-volume production runs where the setup time and capital investment can be amortised over large quantities. For small batch production (fewer than 1,000 holes per setup), a single-spindle machine is more economical.

What industries use multispindle deep hole drilling the most? ​

Heat exchanger manufacturing (tube sheets, baffle plates) is the largest application. Other major industries include automotive (transmission shafts, fuel injection components), oil and gas (valve bodies, drilling equipment), hydraulics (cylinder blocks, manifold blocks), and medical device manufacturing.

How is tool breakage detected in multispindle drilling? ​

Each spindle should have independent torque and feed force monitoring. When a tool breaks on one spindle, the control system detects the abnormal torque signal and retracts only that spindle while the others continue. This prevents scrapping the entire workpiece due to a single tool failure.

What is the difference between fixed-pitch and adjustable-pitch multispindle machines? ​

Fixed-pitch machines have spindles mounted at fixed centre distances and cannot be reconfigured for different hole patterns. Adjustable-pitch machines (TARUS DHMS) allow spindle spacing to be changed, typically within a defined range. Fixed-pitch machines are less expensive but less flexible.

How do I calculate the breakeven volume for a multispindle machine? ​

Compare the total cost per hole including capital recovery, labour, tooling, coolant, and maintenance for single-spindle vs multispindle options. The breakeven volume is the annual production quantity at which the multispindle total cost equals the single-spindle total cost — typically 50,000–200,000 holes per year for a 4-spindle machine.