Choosing the Correct Stepper Motor for Your CNC Machine

Choosing the correct motor for a CNC machine can quickly become confusing.

NEMA 17, NEMA 23 or NEMA 34? Open loop or closed loop? Separate driver or integrated driver? And how much torque do you actually need?

Choosing the biggest motor isn't necessarily the answer.

The correct motor depends on the machine you're building, the weight each axis needs to move, the mechanical drive system, required speed and acceleration, and whether you need encoder position feedback.

This guide breaks down the main motor systems available from CNC Online South Africa and explains where each option fits.

Quick Guide: CNC Motor Options

This table is a starting point rather than a substitute for proper motor sizing. The motor should always be selected according to the requirements of the individual machine.

What Do NEMA 17, NEMA 23 and NEMA 34 Mean?

One of the first mistakes to avoid is assuming the NEMA number tells you exactly how powerful a motor is.

It doesn't.

The NEMA designation primarily describes the physical frame size of the motor.

A larger frame generally allows a manufacturer to build motors capable of producing more torque, but two motors with the same NEMA frame can still have very different specifications.

For example, CNC Online's NEMA 23 range includes motors with several different torque ratings.

So instead of asking:

"Do I need a NEMA 23 or NEMA 34?"

A better question is:

"What motor size, torque and control system suit the axis I'm trying to move?"

You need to consider:

• Motor frame size
• Required torque
• Operating speed
• Moving mass
• Acceleration
• Mechanical drive system
• Driver
• Power supply
• Open-loop or closed-loop control

All of these influence how the machine will perform.

NEMA 17 — For Lightweight Motion

NEMA 17 motors are commonly used where the moving load is relatively light.

Typical applications include:

• 3D printers
• Extruders
• Small laser engravers
• Lightweight Z-axes
• Robotics
• Small positioning systems
• Automation projects
• Very small CNC machines

Their compact size makes them useful where large amounts of torque aren't required.

Once you begin moving a larger CNC gantry or heavier mechanical assembly, NEMA 23 or NEMA 34 systems will normally become more appropriate.

NEMA 23 — A Versatile Choice for CNC Machines

NEMA 23 is one of the most useful motor sizes for small and medium CNC applications.

CNC Online offers NEMA 23 systems in three main configurations:

1. Open loop
2. Closed loop with a separate driver
3. Closed loop with an integrated driver

This means choosing a NEMA 23 is not just about torque. You also need to decide how the motor will be controlled and how you want the electrical system arranged.

Option 1: NEMA 23 Open Loop

An open-loop stepper system is the traditional and simplest configuration.

The CNC controller sends step and direction commands to the driver, which controls the motor. There is no encoder continuously feeding the motor's position back to the driver.

CNC Online offers NEMA 23 open-loop motor and DM556 driver packages in:

• 1.2Nm
• 2.2Nm
• 3Nm

These systems use the DM556 microstep driver.

NEMA 23 open loop can be suitable for:

• Small CNC routers
• Medium CNC routers
• Plasma systems
• Laser machines
• DIY CNC builds
• General automation
• Machines with predictable axis loads

The major advantage is simplicity and cost effectiveness.

When the motor has been correctly sized and the machine operates within its design limits, an open-loop stepper system can provide accurate and repeatable motion.

The limitation is that there is no encoder monitoring the motor's actual position.

If the motor cannot keep up with the commanded movement because of excessive load, aggressive acceleration or another problem, the system doesn't have the same position-error feedback available in a closed-loop system.

Option 2: NEMA 23 Closed Loop with a Separate Driver

A closed-loop stepper system adds encoder feedback.

The encoder allows the driver to monitor motor position and compare it with the commanded movement.

CNC Online's NEMA 23 closed-loop systems combine an encoder-equipped motor with the HBS57H hybrid servo driver.

Motor options include:

• 1.5Nm
• 2.2Nm
• 3Nm

The motor and driver remain separate, with the driver normally installed inside the machine's electrical enclosure.

Closed loop is worth considering when:

• The gantry is heavier
• Loads can change
• Higher acceleration is required
• The machine operates for long periods
• Losing position could ruin expensive material
• Greater confidence in axis positioning is required

Closed-loop systems use encoder feedback to monitor motor position, detect following error and correct positioning errors within the operating limits of the system.

However, closed loop does not remove the need to size the motor correctly.

It also cannot compensate for every possible mechanical problem elsewhere in the machine, such as backlash, a loose coupling or problems between the motor and the load.

The motor still needs sufficient torque for the application.

What Does "Hybrid Servo Driver" Mean?

You may see drivers such as the HBS57H and HBS86H described as hybrid servo drivers.

It's important not to confuse these with conventional AC servo systems.

A closed-loop stepper system uses a stepper motor with encoder feedback and a compatible closed-loop driver.

An AC servo system uses a different type of motor and dedicated servo drive.

CNC Online stocks both.

HBS57H / HBS86H = Closed-loop stepper systems

600W / 1000W / 1500W / 2000W systems = AC servo systems

Option 3: NEMA 23 Integrated Closed Loop

CNC Online also stocks integrated closed-loop NEMA 23 motors .

Instead of installing a separate motor and driver, an integrated system combines the:

• Stepper motor
• Encoder
• Closed-loop driver electronics

into one compact unit.

CNC Online's integrated NEMA 23 range includes:

• 1.5Nm with side-mounted driver
• 1.5Nm with rear-mounted driver
• 2Nm with rear-mounted driver
• 3Nm with rear-mounted driver

This gives customers a choice of both torque and physical layout.

Why Choose an Integrated Motor?

The main advantage is simpler installation.

Because the driver is mounted directly to the motor, you don't need a separate motor driver installed inside the main electrical enclosure.

That can reduce:

• Motor-to-driver wiring
• Cable runs
• Control-box components
• Control-box space requirements
• Installation complexity

You still benefit from encoder-based closed-loop control, but the motor and driver are packaged together.

Integrated motors are particularly useful for new CNC builds, upgrades, compact machines and systems where reduced wiring is important.

Integrated vs Separate Closed-Loop Systems

Choose a separate HBS57H system if you prefer all the motor drivers located together inside a central electrical enclosure.

Choose an integrated system if you want less wiring and fewer components inside the main control box.

Neither arrangement is automatically better. The correct choice depends on the layout and requirements of the machine.

When Should You Move Up to NEMA 34?

NEMA 34 motors become relevant when an axis requires significantly more torque.

Typical applications can include:

• Large CNC routers
• Heavy gantries
• Milling equipment
• Large X and Y axes
• Large rack-and-pinion axes
• Heavy ball-screw-driven assemblies
• Industrial automation
• Large rotary systems

But bigger does not automatically mean better.

An oversized motor can increase cost, weight, rotational inertia and electrical requirements without necessarily improving the performance of a smaller machine.

The objective is not to install the largest motor available. It's to install enough motor for the application.

NEMA 34 Open Loop

For machines requiring more torque without encoder feedback, CNC Online offers NEMA 34 open-loop systems .

These use the DM860H microstep driver.

A NEMA 34 open-loop system may make sense when:

• A NEMA 23 doesn't provide sufficient torque
• Loads are predictable
• Encoder feedback isn't required
• The motor has been correctly sized
• A straightforward system is preferred

This provides a relatively simple way to achieve considerably more available stepper-motor torque.

NEMA 34 Closed Loop

For heavier applications where both torque and position feedback are important, CNC Online offers NEMA 34 closed-loop systems .

These combine encoder-equipped NEMA 34 motors with the HBS86H hybrid servo driver.

Available torque options include:

• 4.5Nm
• 8.5Nm
• 12Nm

NEMA 34 closed loop may suit:

• Large CNC routers
• Heavy moving gantries
• Milling applications
• Large rotary axes
• Industrial automation
• Machines operating under changing loads

This gives you the higher torque capability of the larger motor together with encoder-based position monitoring.

Open Loop vs Closed Loop vs Integrated

Open Loop

Motor + separate driver + no encoder feedback

Advantages:

• Simple
• Cost effective
• Widely used
• Straightforward setup

Best suited to applications where the motor can be confidently sized for a predictable load.

Closed Loop

Motor + encoder + separate closed-loop driver

Advantages:

• Encoder feedback
• Following-error monitoring
• Drivers located together in the control box
• Suitable for more demanding applications

Best suited where greater confidence in motor positioning is required.

Integrated Closed Loop

Motor + encoder + driver in one unit

Advantages:

• Encoder feedback
• Reduced wiring
• Fewer control-box components
• Compact installation
• Cleaner electrical layout

Best suited where closed-loop control is wanted together with a simpler installation.

Don't Choose a Motor Using Holding Torque Alone

Stepper motors are often advertised using figures such as 1.2Nm, 2.2Nm, 3Nm, 4.5Nm, 8.5Nm or 12Nm.

These are useful specifications, but they don't tell the whole story.

A motor's holding torque describes its ability to resist movement while stationary.

Once the motor begins rotating, available torque changes with speed.

That means a motor with a large holding-torque figure doesn't necessarily provide that same torque while the CNC axis is moving at its operating speed.

A CNC axis needs enough usable torque to:

• Accelerate the moving mass
• Overcome mechanical resistance
• Drive the transmission
• Maintain the required feed rate
• Decelerate the load
• Continue operating reliably at speed

This is why proper stepper selection should consider the motor's torque-speed characteristics, not only its holding-torque figure.

The Driver and Power Supply Matter Too

The motor isn't working alone.

The driver and power supply have a major influence on how the motor performs, particularly as speed increases.

A stepper motor's windings have electrical inductance, and the driver needs to build current in those windings rapidly as the motor turns.

The motor, driver and power supply therefore need to be considered as one system.

Typical CNC Online combinations include:

• NEMA 23 Open Loop → DM556
• NEMA 23 Closed Loop → HBS57H
• NEMA 23 Integrated Closed Loop → Driver built into the motor
• NEMA 34 Open Loop → DM860H
• NEMA 34 Closed Loop → HBS86H

You also need to consider supply voltage, motor current, controller compatibility, wiring, cooling and the mechanical transmission.

Simply connecting a larger motor doesn't automatically make an axis perform better.

Your Mechanical Drive System Matters

Motor torque is only part of the equation.

The motor usually moves the CNC axis through a mechanical system such as:

• Ball screw
• Lead screw
• Rack and pinion
• Belt and pulley
• Gearbox

A motor's Nm rating does not directly tell you how much linear force the CNC axis will produce.

Factors such as ball-screw lead, pinion diameter, pulley diameter, gear ratio and mechanical efficiency all change how motor torque is converted into machine movement.

For example, a lightweight Z-axis driven by a ball screw may require a very different motor from a long rack-and-pinion Y-axis moving a heavy gantry.

You therefore don't necessarily need identical motors on every axis.

Each axis should be considered individually.

What About Servo Motors?

There comes a point where a machine may require something different from a stepper system.

CNC Online also stocks complete AC servo motor systems in:

• 600W
• 1000W
• 1500W
• 2000W

Servo systems can become relevant where an application requires characteristics such as:

• Higher operating speeds
• Strong performance across a broader speed range
• Advanced position feedback
• High-performance acceleration and deceleration
• Industrial-duty motion control

However, a servo isn't automatically the better choice simply because it's a more advanced system.

For many CNC machines, a correctly sized open-loop or closed-loop stepper system remains the more practical and economical solution.

Stepper motors vs servo motors is a subject on its own, which we'll cover in a separate CNC Online guide.

So Which Motor Should You Choose?

Choose NEMA 17 if:

You're building a lightweight machine such as a 3D printer, small laser engraver or compact positioning system.

Choose NEMA 23 Open Loop + DM556 if:

You're building a small-to-medium CNC machine and want a straightforward, economical motion system.

Choose NEMA 23 Closed Loop + HBS57H if:

You want encoder feedback while keeping all your motor drivers together inside a conventional control enclosure.

Choose NEMA 23 Integrated Closed Loop if:

You want encoder feedback with reduced wiring and fewer components inside the electrical enclosure.

Choose NEMA 34 Open Loop + DM860H if:

Your machine requires substantially more torque but encoder feedback isn't necessary.

Choose NEMA 34 Closed Loop + HBS86H if:

You're building a larger or heavier machine where higher torque and encoder position feedback are both important.

Consider a Servo System if:

Your machine's required speed, acceleration or overall motion-control performance moves beyond what an appropriately sized stepper system can practically provide.

Example: Two Very Different CNC Routers

Machine A: Compact CNC Router

The machine has:

• Lightweight aluminium gantry
• Short travel
• Smaller spindle
• Ball-screw-driven axes

A suitably sized NEMA 23 system may provide everything the machine requires.

The builder could choose between:

• Open loop for simplicity
• Closed loop with HBS57H for encoder feedback
• Integrated closed loop for reduced wiring

Machine B: Large CNC Router

Now consider a machine with:

• Heavy gantry
• Long Y-axis
• Larger spindle
• Large rack-and-pinion axes
• Much greater moving mass

Its requirements are completely different.

A NEMA 34 system may be more appropriate on the heavier axes.

The builder could choose between:

• NEMA 34 open loop + DM860H
• NEMA 34 closed loop + HBS86H

The correct choice comes from the requirements of the machine — not simply from choosing the largest motor.

8 Things to Check Before Ordering

1. What type of machine are you building?
2. How much mass does the axis need to move?
3. What mechanical drive system are you using?
4. What maximum axis speed do you require?
5. How quickly does the axis need to accelerate?
6. How much usable torque is required across the operating speed range?
7. Do you need open-loop or closed-loop control?
8. Would a separate or integrated driver suit the machine better?

If you're unsure about some of these answers, don't choose a motor based only on the NEMA size or holding-torque number.

Looking at the complete motion system before ordering can prevent expensive changes later.

Final Thoughts

There is no single "best" stepper motor for every CNC machine.

The right choice is the motor and control system that matches the machine.

For lightweight applications, NEMA 17 may be sufficient.

For many small and medium CNC machines, NEMA 23 provides an excellent range of options, including open loop, conventional closed loop and integrated closed loop.

For larger machinery and heavier axes, NEMA 34 provides considerably more torque capability, again with open-loop and closed-loop systems available.

And for machines requiring different speed and motion-control characteristics, CNC Online's 600W to 2000W servo systems provide another option.

The goal isn't to buy the biggest motor.

It's to choose the right motor, driver and mechanical system for the machine you're building.

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Need Help Choosing?

If you're unsure which motor or driver is right for your CNC machine, browse CNC Online's Stepper Motors, Servo Motors & Drivers range or contact the CNC Online team.

The most useful information to provide includes:

• Machine type
• Axis drive system
• Moving load
• Required speed
• Intended application

From there, it's much easier to identify a suitable motor and driver combination for the build.