What Is a Multi-Spindle Drilling Head?

A multi-spindle drilling head allows two or more holes to be drilled simultaneously in a single machine cycle. Instead of producing each hole individually, one drilling machine drives multiple output spindles through a common geared head, with each spindle carrying its own cutting tool.

The spindle positions can be adjusted to reproduce the required hole pattern, making variable multi-spindle heads particularly useful for repetitive production work where the same component requires several holes at fixed centres.

Multi-spindle heads can also be configured for tapping, allowing several threaded holes to be produced simultaneously.

Why Use a Multi-Spindle Drilling Head?

The principal advantage of a multi-spindle drilling head is production efficiency. Where a component requires several holes, producing them simultaneously can substantially reduce machining time compared with drilling each hole individually.

• Reduced cycle time – multiple holes can be drilled in one machine cycle.
• Higher output – more components can be produced within the same available machine time.
• Consistent hole patterns – once the spindle positions are correctly set, the same pattern is repeated from component to component.
• Reduced operator input – the component does not need to be repositioned for every individual hole.
• Drilling or tapping – suitable heads can perform multiple drilling or tapping operations simultaneously.

The concept is particularly effective where the same hole pattern is repeated across a batch of components, turning a conventional drilling operation into a significantly more productive manufacturing process.

How Multi-Spindle Drilling Heads Work

A multi-spindle drilling head takes the rotary drive from a single drilling machine spindle and distributes it through an internal gear system to multiple output spindles.

Each output spindle carries its own drill or tap. The spindle positions can be adjusted within the operating range of the particular head, allowing the tools to be positioned to match the required hole pattern.

Once correctly set:

• The workpiece is positioned beneath the head.
• All cutting tools rotate simultaneously.
• The drilling machine feeds the complete head towards the workpiece.
• All holes are produced during the same feed cycle.

This arrangement means a conventional drilling machine or production drilling unit can perform a multiple-hole operation with a single spindle feed, without requiring each hole to be drilled separately.

How Is the Multi-Spindle Head Connected to the Drilling Machine?

The multi-spindle head must be correctly matched to the drilling machine both mechanically and in terms of the machine spindle connection.

On conventional industrial pillar drills and drilling machines, one of the most common spindle systems is the Morse Taper (MT).

Morse Taper Connections

Morse Tapers are designated by size, with common industrial drilling-machine connections including MT1, MT2, MT3, MT4 and MT5.

The taper size generally increases with the physical size and capacity of the drilling machine. Smaller drilling machines may use MT1 or MT2, while larger industrial machines commonly use MT3, MT4 or MT5.

When specifying a multi-spindle head, the actual taper fitted to the machine must be confirmed. An adaptor is then selected to connect that machine spindle to the drive system of the multi-spindle head.

Jacobs Taper and Other Spindle Connections

Morse Taper is not the only machine connection available. Depending on the drilling machine, the head can also be configured for Jacobs Taper connections such as B10, B12, B16 and B18, as well as other industrial spindle and taper arrangements where suitable adaptors are available.

Other machine interfaces may include arrangements such as ISO30 and ISO40, depending on the machine and application.

Adaptor, Drive Block and Connection Collar

The complete connection typically consists of:

• Machine spindle – the existing spindle or quill arrangement on the drilling machine.
• Spindle adaptor – selected to suit the machine connection, such as MT1, MT2, MT3, MT4, MT5, Jacobs Taper or another suitable interface.
• Drive block – transmits the rotational drive from the machine spindle into the multi-spindle head.
• Connection collar – locates and supports the body of the multi-spindle head on the drilling machine and prevents the head itself from rotating.

The connection collar is particularly important. Its dimensions must correspond with the spindle, quill and housing geometry of the particular drilling machine. For this reason, the drilling machine make and model, spindle connection and relevant collar dimensions should be established before a head is ordered.

This is why selecting a multi-spindle head involves more than simply choosing the required number of spindles and drilling capacity. The head must suit both the component being manufactured and the drilling machine that will drive it.

How Are Drills and Taps Held in a Multi-Spindle Head?

Each output spindle requires its own cutting tool. The toolholding arrangement depends upon the head, the cutting tool and whether the operation is drilling or tapping.

Drilling with ER Collets

For drilling operations, ER collets provide a compact and accurate method of holding individual drills.

Each drill is fitted into the appropriate collet on its respective spindle. Different collet sizes allow a range of tool diameters to be accommodated within the capacity of the head.

Individual tool length can also be adjusted on applicable head configurations. This is important on a multi-spindle head because the cutting edges of the drills need to be correctly positioned relative to one another and to the workpiece.

Tapping Toolholding

For tapping applications, the toolholding arrangement differs from standard drilling.

A tap must be positively driven through its square section, rather than relying solely on friction from a conventional round collet. Tapping therefore uses tooling designed specifically to locate and drive both the tap shank and the square.

Depending on the head and tapping arrangement selected, the spindle itself may also need to be specifically prepared or configured for the tapping system.

This is important because a head intended purely for drilling should not automatically be assumed to be correctly configured for tapping. The required tap size, square size and tapping spindle/toolholding arrangement should therefore be specified when ordering.

Spindle Configurations and Adjustable Hole Patterns

Multi-spindle drilling heads are available with different numbers and arrangements of spindles to suit the required hole pattern.

• 2-spindle heads – for producing two holes simultaneously.
• 3-spindle heads – for triangular or other three-hole patterns.
• 3-spindle linear heads – for applications where three holes are positioned in a straight line.
• 4-spindle heads – for rectangular, square and other four-hole patterns.
• Single decentralised spindle heads – for applications where the drilling position needs to be offset from the machine spindle centreline.

Larger heads can also accommodate special spindle arrangements for particular production applications.

Adjustable Spindle Centres

One of the main advantages of a variable-axis multi-spindle head is that the individual spindles can be positioned to match the required hole pattern, rather than being permanently manufactured at one fixed centre distance.

Each head has a defined minimum and maximum spindle centre distance. The available adjustment range depends on the physical size of the head, the number of spindles and their arrangement.

The hole pattern therefore needs to be considered as a complete geometry. For correct selection, a drawing should ideally show the position of every hole, hole diameter and centre-to-centre dimensions. This allows the spindle arrangement to be checked against the adjustment envelope of the proposed head.

Why Minimum Centre Distance Matters

Each spindle assembly occupies physical space. If two required holes are positioned too close together, the spindle bodies and tooling can interfere with one another, even though the individual hole diameters themselves are within the drilling capacity of the head.

Conversely, a hole pattern with widely spaced holes may require a physically larger head to provide sufficient spindle adjustment.

For this reason, the correct multi-spindle head is selected from a combination of hole diameter, number of holes, hole pattern and spindle centre distances – not drilling diameter alone.

Drilling, Tapping and Machine Capacity

Multi-spindle heads can be used for both drilling and tapping, but the two operations place different demands on the head, tooling and drilling machine.

Multi-Spindle Drilling

In a drilling application, all drills enter the workpiece simultaneously. This can dramatically reduce cycle time, but it also means that the machine is effectively performing several drilling operations at the same time.

The drilling machine must therefore have sufficient spindle power, torque, rigidity and feed capacity for the combined cutting load.

For example, drilling four holes simultaneously should not be treated as equivalent to drilling one hole of the same diameter. The load generated by all four cutting tools must be considered when selecting both the multi-spindle head and the machine driving it.

Multi-Spindle Tapping

Tapping requires additional consideration because the taps must rotate and feed at the correct relationship to the thread pitch.

The head must also be supplied with the appropriate tapping spindle and toolholding arrangement.

When specifying a multi-spindle head for tapping, it is therefore important to provide the thread size, thread pitch, material, number of tapped holes and required hole pattern, as well as details of the machine on which the head will be installed.

Understanding Drilling Capacity

The stated drilling capacity of a multi-spindle head refers to the maximum recommended drilling diameter for that particular head series, but this should not be considered independently of the drilling machine or the number of holes being produced.

As the required hole diameter increases, the cutting forces and torque required also increase. With a multi-spindle head, those requirements are multiplied because all cutting tools are operating simultaneously.

The Drilling Machine Must Also Have Sufficient Capacity

Selecting a head capable of drilling the required diameter does not automatically mean that the drilling machine can perform the operation.

The machine must have sufficient:

• Motor power and spindle torque
• Spindle speed range
• Feed capability
• Spindle and quill rigidity
• Overall machine rigidity

For example, a drilling machine that can comfortably drill a single Ø20 mm hole should not automatically be assumed capable of drilling four Ø20 mm holes simultaneously through a multi-spindle head.

The material being drilled, hole depth, cutting speed, feed rate and number of simultaneously engaged tools all affect the actual cutting load.

How to Specify the Correct Multi-Spindle Head

Correct selection starts with the component and the operation, not simply the model of drilling machine.

The following information should be established before selecting a head:

• Number of holes – how many holes need to be produced simultaneously.
• Hole diameter or thread size – including tap size and pitch for tapping applications.
• Hole pattern – preferably supplied as a dimensioned drawing showing the position of every hole.
• Centre distances – both the closest and furthest distances between the required spindle positions.
• Workpiece material – for example mild steel, stainless steel, aluminium or plastics.
• Material thickness or hole depth – required to assess the actual cutting operation.
• Drilling or tapping – this affects both head selection and the required spindle/toolholding arrangement.
• Drilling machine make and model – required to establish compatibility with the proposed head.
• Machine spindle connection – for example MT2, MT3, MT4, MT5, Jacobs Taper or another spindle interface.
• Connection collar dimensions – where required to correctly match the head to the machine quill or spindle housing.
• Machine power and speed range – the machine must be capable of driving all of the cutting tools simultaneously.

A Drawing Is Usually the Best Starting Point

For most applications, the simplest and safest method is to provide a dimensioned drawing of the required hole pattern together with details of the material and drilling machine.

This considerably reduces the possibility of selecting a head that has sufficient drilling capacity but cannot physically achieve the required hole pattern or cannot be correctly fitted to the drilling machine.

Matching the Multi-Spindle Head to the Drilling Machine

Once the hole pattern and required head have been established, the drilling machine itself must be checked for suitability.

Will the Head Physically Fit the Machine?

The machine spindle connection must be identified – for example MT2, MT3, MT4 or MT5 Morse Taper, Jacobs Taper or another spindle interface.

The appropriate adaptor, drive arrangement and connection collar can then be selected.

The physical dimensions around the machine spindle and quill must also provide sufficient clearance for the head and its connection collar.

Is the Machine Powerful and Rigid Enough?

A multi-spindle head places a greater load on the drilling machine than a single cutting tool. The machine must therefore have sufficient power, torque, spindle rigidity and feed capability for all of the drills or taps operating simultaneously.

The physical size and weight of the head should also be appropriate for the drilling machine. A large production multi-spindle head should not be fitted to a small light-duty bench drill simply because a suitable taper adaptor can be manufactured.

Existing Machines Can Often Be Converted

One of the significant advantages of this type of system is that a suitable existing industrial drilling machine can potentially be converted from a single-spindle operation to a multiple-hole production operation without replacing the complete machine. Where the machine has adequate capacity and rigidity, fitting the correct head, adaptor and connection collar can provide a relatively straightforward way of increasing productivity.

Typical Industrial Applications

Multi-spindle drilling heads are particularly suited to repetitive production applications where the same hole pattern is required on a large number of components.

Typical applications include:

• Fabricated steel components – drilling repeated bolt-hole patterns in brackets, plates and welded assemblies.
• Flanges and mounting plates – producing several equally spaced or patterned holes in a single operation.
• Automotive and transport components – repetitive drilling or tapping of production parts.
• Machined components – secondary drilling and tapping operations where several holes share a common pattern.
• Electrical and mechanical enclosures – producing repeated mounting-hole arrangements.
• Furniture, architectural and general fabrication components – where identical hole patterns are required across production batches.
• Dedicated production drilling machines – where a multi-spindle head forms part of a purpose-built drilling or tapping station.

Particularly Effective for Batch and Production Work

A multi-spindle head provides the greatest benefit when the same component or hole pattern is produced repeatedly.

For example, if a component requires four mounting holes, a conventional single-spindle drilling operation may require four separate drilling positions. With a correctly configured four-spindle head, all four holes can potentially be produced during one feed of the drilling machine.

The resulting reduction in handling, positioning and individual drilling operations can make multi-spindle drilling particularly effective for medium- and high-volume production, while still allowing adjustable heads to be reconfigured for future jobs within their operating range.

Multi-Spindle Head Range and Selection

Once the application requirements have been established, the appropriate head series can be selected according to the required drilling capacity, hole pattern, number of spindles and centre-distance range.

The range should not simply be viewed as small, medium and large heads. Moving to a larger series provides greater drilling capacity and can accommodate different hole-pattern requirements, but the correct selection still depends on the complete application.

For example, an application requiring four Ø6 mm holes would not automatically require the smallest head capable of accepting a Ø6 mm drill. The required centre distances and complete hole pattern must also fit within that head’s adjustment range.

Conversely, there is little benefit in selecting a substantially larger head than required if a smaller series comfortably accommodates the drilling diameter and complete hole pattern.

The objective is to select the smallest suitable head that satisfies the complete drilling or tapping application while remaining compatible with the drilling machine on which it will be installed.

Need Help Selecting a Multi-Spindle Drilling Head?

Selecting the correct multi-spindle drilling head requires more than simply knowing the number and diameter of the holes. The hole pattern, centre distances, workpiece material, drilling or tapping operation, machine spindle and available machine capacity all need to be considered together.

At The Workshop Press Company UK, we can help specify a multi-spindle head to suit both the component and the drilling machine.

For a new application, the most useful information to provide is:

• A dimensioned drawing of the hole pattern
• Hole diameters or thread sizes and pitches
• Number of holes
• Workpiece material and thickness
• Whether the operation is drilling or tapping
• Drilling machine make and model
• Machine spindle connection, if known
• Photographs or dimensions of the machine spindle and quill where required

From this information, we can establish the appropriate head series, spindle configuration, adjustment range, toolholding and machine connection.

Multi-spindle heads can provide a particularly effective way of converting a conventional industrial drilling machine into a high-productivity multiple-hole drilling or tapping system, without the cost and complexity of moving the operation to a CNC machine or dedicated machining centre.

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