Choosing the Correct ATC Spindle for Your CNC Router

For CNC routers running repeated jobs with several different cutters, one of the biggest productivity improvements can be moving from a conventional spindle to an Automatic Tool Change (ATC) spindle.

However, choosing an ATC spindle is not simply a matter of choosing a power rating. The spindle, tool-holder system, CNC controller, VFD, compressed-air supply, cooling system, tool rack and Z-axis all need to work together.

CNC Online currently offers two very different ATC spindle platforms: 2.2kW ISO20 ATC and 7.5kW BT30 ATC.

This guide explains how an ATC system works, the difference between ISO20 and BT30, and what needs to be considered before adding automatic tool changing to a CNC router.

ATC Is More Than Just a Different Spindle

With a conventional CNC spindle, the cutter is normally fitted directly into an ER collet and secured with a collet nut. When another cutter is required, the machine is stopped and the operator changes the tool manually.

An ATC spindle works differently. The cutter is installed into a removable tool holder, such as ISO20 or BT30. The tool holder is retained inside the spindle and can be released automatically when the CNC machine performs a tool change.

A complete ATC system therefore normally includes:

• ATC spindle
• Matching tool holders
• Tool-holder rack or magazine
• Tool-holder clamps
• ATC-capable CNC controller
• Compressed-air supply
• Correctly matched VFD
• Spindle cooling system
• Tool-height setting or tool-length offset system

This is why an ATC spindle should be treated as part of a complete machine system rather than as a simple replacement for a conventional spindle.

How an Automatic Tool Change Works

During a machining program, the CNC controller can call for a different tool when the next operation requires it.

A typical automatic tool-change sequence can include:

1. The spindle stops.
2. The machine moves to the programmed tool-rack position.
3. The current tool holder is positioned in its tool-holder clamp.
4. The spindle releases the current tool holder.
5. The machine moves to the next tool position.
6. The new tool holder is collected and clamped into the spindle.
7. The correct tool-length information is applied.
8. Machining continues with the new cutter.

The exact sequence depends on the controller, spindle and tool-rack design, but the important point is that the controller must be capable of managing the complete tool-change process.

CNC Online's DDCS Expert 5 Axis Controller supports multiple spindle modes as well as straight, gantry and disk-type tool magazines, making it suitable for advanced CNC systems where automatic tool changing is required.

2.2kW ISO20 vs 7.5kW BT30

Note: Electrical supply, VFD sizing, pneumatic requirements and other installation requirements should always be confirmed for the specific spindle and CNC machine before installation.

2.2kW ISO20 ATC – The Practical CNC Router Option

The 2.2kW Water Cooled ISO20 ATC Spindle is the more practical ATC platform for many CNC router applications.

Its confirmed specifications include:

• 2.2kW spindle power
• ISO20 automatic tool-change interface
• 24,000 RPM maximum speed
• 800Hz operating frequency
• 80mm spindle diameter
• Water cooling
• Runout of ≤0.005mm
• HY6005C P4 ×2 and SM6004C P4 ×1 bearing configuration

Instead of fitting the cutter directly into the spindle, cutters are installed into ISO20 ER20 tool holders.

This allows frequently used cutters to remain prepared in individual holders. A CNC router could, for example, have separate holders ready for:

• Compression cutters
• Up-cut or down-cut cutters
• V-bits
• Engraving cutters
• Drills
• Finishing cutters

The machine can then select the required tool holder automatically during the machining program instead of waiting for the operator to change the cutter manually.

For CNC routers where the main objective is reducing manual tool changes while keeping the spindle package relatively compact, ISO20 is generally the more practical ATC platform.

7.5kW BT30 ATC – For Heavier Production Machines

The 7.5kW Water Cooled BT30 ATC Spindle belongs to a considerably heavier class of CNC system.

Its specifications include:

• 7.5kW rated power
• 380V rated voltage
• 16A rated current
• BT30 automatic tool interface
• 24,000 RPM maximum speed
• 800Hz operating frequency
• Maximum torque of 8.0Nm
• 4-pole motor
• Water or oil cooling
• NPN tool-release sensor
• 29kg spindle weight

The larger BT30 tooling platform is intended for heavier production applications where the machine can properly use the additional spindle power, torque and tooling capacity.

The matching BT30 ER25 Tool Holder uses ER25 collets, providing a larger collet system than the ER20 system used with the ISO20 holders.

One of the most important considerations is the spindle's 29kg weight.

That mass needs to be supported and accelerated by the Z-axis. The spindle mount, linear rails, ball screw or drive system, motor, gantry and overall machine structure must therefore be suitable for the additional load.

The 7.5kW BT30 spindle should not be selected simply because it has more power. It makes sense when the entire CNC machine has been designed around a spindle of this size and weight.

ISO20 or BT30?

The decision between ISO20 and BT30 should be based on the CNC machine and the work it needs to perform rather than spindle power alone.

Choose ISO20 when:

• You are building or upgrading a CNC router
• You want automatic tool changing without moving to a very heavy spindle system
• 2.2kW provides sufficient spindle power for your work
• You mainly machine timber, MDF, plastics, composites and similar router materials
• You want a compact high-speed ATC setup

Choose BT30 when:

• The CNC machine is designed for heavier production work
• You require substantially more spindle power and torque
• The Z-axis and gantry can support a 29kg spindle
• A suitable 380V electrical supply is available
• The larger BT30 / ER25 tooling platform is beneficial for the application

For many conventional CNC router applications, the 2.2kW ISO20 ATC spindle is the more practical starting point.

The 7.5kW BT30 is better suited to machines that have specifically been designed to take advantage of the additional spindle power and heavier tooling system.

The Tool Rack Is an Important Part of the System

An ATC system needs somewhere to store each tool holder when it is not being used.

A common CNC router setup uses a linear tool rack with individual tool-holder clamps mounted at accurately programmed positions.

CNC Online stocks ISO20 Tool Holder Clamps and BT30 Tool Holder Clamps for retaining and positioning the corresponding tool holders.

Each tool position is assigned a known location in the CNC controller. During a tool change, the machine moves the spindle to the correct position so that the tool holder can be returned to or collected from the rack.

Tool-rack positioning and alignment are important. The spindle and tool holder need to enter and leave each position consistently without unnecessary side loading or misalignment.

ATC Requires Compressed Air

ATC spindles use a pneumatic system as part of the automatic tool-release and clamping process.

The CNC machine therefore requires a suitable supply of clean, dry compressed air for reliable operation of the tool-change system.

The exact required pressure and airflow depend on the spindle being installed. These requirements should be confirmed for the specific spindle before the pneumatic system is configured.

This is particularly important because an ATC system depends on reliable tool release and clamping every time the machine performs a tool change.

Choosing the Correct VFD

The VFD needs to match more than the spindle's kW rating.

Both CNC Online ATC spindles operate at up to 800Hz, so the selected VFD needs to support the required operating frequency as well as the correct spindle power, voltage and current.

CNC Online's H100 Mini VFD supports frequencies up to 1000Hz, which provides the frequency range required for compatible 800Hz ATC spindle applications.

For the 2.2kW ISO20 spindle, a correctly specified H100 Mini can therefore be a practical VFD option where its power, voltage and current ratings match the spindle installation.

Frequency capability alone does not make a VFD compatible. Power rating, input supply, output voltage, output current and spindle parameters must all be correctly matched and programmed.

The 7.5kW BT30 spindle requires an appropriately sized VFD that matches its 7.5kW, 380V and 800Hz requirements.

Tool Length Must Be Managed

Every cutter installed in an ATC system can have a different overall length.

The CNC controller therefore needs accurate tool-length information so that changing from one cutter to another does not change the programmed cutting depth.

For automated systems, a fixed tool setter can be used as part of the tool-height measurement process.

CNC Online's Z-Axis Automatic Tool Height Setter is designed to quickly and accurately reset tool height after tool changes and is suitable for automated tool-setting applications.

It is useful to think of these as two separate parts of the system:

• The tool rack tells the machine where each tool is stored.
• The tool-length system tells the machine where the cutting edge of each tool is.

Both need to be configured correctly for reliable automatic machining.

Cooling Still Matters

Automatic tool changing does not remove the spindle's cooling requirements.

The 2.2kW ISO20 ATC spindle is water cooled and requires a suitable coolant circuit to manage spindle temperature during operation.

The 7.5kW BT30 spindle can use water or oil cooling and needs to be installed with the correct cooling system for the spindle.

For more information about water-cooled spindle systems, see our Choosing the Correct Water Cooled Spindle for Your CNC Router guide.

Before Upgrading a CNC Router to ATC

Before purchasing an ATC spindle, check the complete CNC system rather than only the spindle specifications.

• Controller: Can it manage an automatic tool-change sequence and tool magazine?
• VFD: Can it provide the correct power, voltage, current and operating frequency?
• Pneumatics: Is a clean and reliable compressed-air supply available?
• Tool rack: Is there enough machine travel and space for the required tool positions?
• Tool holders: Are the correct ISO20 or BT30 holders available for the cutters being used?
• Tool measurement: How will tool lengths and Z offsets be established?
• Cooling: Is the correct spindle cooling system installed?
• Z-axis: Can the axis safely support and move the spindle?
• Clearance: Is there enough Z travel for the spindle, tool holder and cutter combination?
• Electrical supply: Is the required electrical supply available for the complete system?

Which ATC Spindle Should You Choose?

For a CNC router where the main objective is to automate multi-tool jobs while keeping the spindle system relatively compact, the 2.2kW ISO20 ATC Spindle will generally be the more practical option.

For a larger production machine engineered around a heavy spindle, 380V power and BT30 tooling, the 7.5kW BT30 ATC Spindle provides a substantial increase in spindle power, torque and tooling capability.

The correct choice ultimately depends on the machine structure, materials, cutter sizes, production requirements and complete ATC system rather than simply choosing the spindle with the highest power rating.

Need Help Choosing?

ATC systems involve more components than a conventional spindle installation. If you are building or upgrading a CNC machine, tell us about your machine size, controller, electrical supply, materials and the type of work you plan to produce.

CNC Online South Africa can help you determine which spindle, tool-holder system and supporting components are best suited to your application.

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Email: sales@cnconline.co.za
WhatsApp: 073 352 8930