Linear Motor Guide: How They Work, Types and CNC Trade-offs

What is a linear motor?

A linear motor is a rotary motor "unrolled" flat. Instead of a rotor spinning inside a stator, a moving part travels along a straight track and pushes the load directly. No mechanical transmission converts rotation into linear travel. It has two parts:

• Primary (forcer or coil unit): carries the windings and usually moves with the load.

• Secondary (magnet track): a row of permanent magnets fixed along the axis.

A rotary motor needs a ball screw, belt or rack to move something in a line. A linear motor drives the load directly, which is where its dynamics come from.

How a linear motor works

Force from a moving magnetic field

Three-phase current in the coils creates a magnetic field that travels along the primary. That field pulls against the permanent magnets in the track, and the resulting force moves the primary along the axis. Reversing the current sequence reverses direction. Thrust follows current, so the drive controls force as well as position.

Commutation and feedback

The drive must know where the coils sit relative to the magnets so it can switch current in the right phase. This is commutation, and it relies on a linear encoder reading position along the track. Nothing mechanical holds the primary in place, so the axis always runs closed-loop on encoder feedback. The encoder and a servo drive are part of the system, not optional extras.

Typical performance ranges

Typical linear-motor CNC axes reach 1–5 g acceleration and 2–5 m/s travel speed. The exact figures depend on moving mass, thrust, drive power and guide quality, so check them against the datasheet of any specific model.

Types of linear motors

Flat (platen) motors

Flat motors are the usual choice for machine tool axes. The ironless/iron-core split above is the main design decision: ironless gives smoother low-speed motion, iron-core gives more thrust for its size. Iron-core primaries pull hard on the magnet track, commonly cited as roughly 3–10× their continuous thrust depending on design. That load lands on the guide and bearings and must be sized for.

U-channel motors

The forcer sits between two magnet rows, which typically cancels most of the magnetic pull on the guide. These motors suit compact, lightly loaded axes.

Tubular motors

A tubular motor has a rod containing magnets and a coil that slides over it. It looks like an actuator, which is why "linear actuator" is used loosely for it.

Induction linear motors

An induction linear motor has no permanent magnets. The primary induces current in a conductive plate and pushes against it, so a long track costs less than a magnet row. Efficiency and force density are typically lower, so they appear mostly in long-travel transport rather than CNC feed axes.

Axis-integration checklist for CNC builders

The motor supplies thrust only. Use this list when laying out a linear-motor axis, then confirm each point against the datasheet of the model you pick.

Sizing an axis: a worked example

This is a generic sizing calculation; confirm the final figures with an application engineer against the motor datasheet. Take an axis with 60 kg of moving mass (table, workpiece, primary) that must accelerate at 2 g (about 19.6 m/s²):

• Force to accelerate: 60 kg × 19.6 m/s² ≈ 1,180 N.

• Add friction, cutting force and margin. Reaching roughly 2,000 N peak is realistic.

• Check that thrust is available at the continuous rating for the duty cycle, not just at peak.

A motor in the 2,000 N class, such as the DLMF-03W 2,000 N flat linear motor, is the right order of magnitude for that load. Whether 2,000 N is peak or continuous, and which cooling it needs, must be confirmed on the product page. For heavier duty, the DLMF-04W high-thrust water-cooled linear motors address the heat that high thrust generates. The DLMF-01W compact flat linear motors suit lighter axes where space is tight. If you want a model matched to your own mass, stroke and acceleration, request a technical consultation.

Advantages and limitations

Advantages (typically)

• No screw backlash, wear or windup, because there is no mechanical transmission.

• High acceleration and speed, since the moving mass is small.

• Accuracy is set mainly by the encoder and control loop.

• Few wearing parts in the drive path.

Limitations

• Higher system cost: encoder, drive and guide often add significantly to the motor price. The linear motor cost factors article breaks down what drives the total.

• Coil heat needs managing.

• Strong magnet attraction complicates handling, and debris can collect on the track.

• No mechanical advantage, so all thrust must come from the motor.

• Vertical axes need a brake or counterbalance.

Linear motor vs ball screw vs linear actuator

The decisive trade-off is holding force and cost versus dynamics. A ball screw holds a load without power and usually costs less, while a linear motor gives higher acceleration and a drive path with nothing to wear. The ball screw advantages and limitations article covers the screw side in depth.

Choose the linear motor when acceleration and contact-free drive justify the extra cost and thermal work. Choose a screw when stroke is long, thrust is high or the axis must hold position unpowered.

Where linear motors are used

• High-speed CNC feed axes

• Semiconductor and inspection stages

• Pick-and-place and automation lines

• Maglev transport, the best-known large-scale example

Is a linear motor right for your machine?

Check these before choosing:

• Acceleration: do you need dynamics a screw cannot deliver?

• Stroke length: longer travel means more magnet track, which adds cost.

• Accuracy target: it depends on encoder resolution and control quality, not the motor alone.

• Thermal budget: can the structure tolerate coil heat, or does the axis need water cooling?

• Vertical loading: if yes, plan a brake or counterbalance.

If most answers favor a linear motor, the next step is matching thrust, size and cooling to your axis layout. Browse linear motors and feed systems for CNC machines, or talk to our engineers about your axis. Rail and ball screw options for the same axis are listed under linear guides and ball screw systems.

Linear motor FAQ

What is a linear motor?

A linear motor is an electric motor laid out flat so it produces straight-line force directly. A coil unit (primary) interacts with a magnet track (secondary), so no screw, belt or gear is needed to turn rotation into linear travel. The load moves with the primary, and an encoder closes the position loop.

Does a linear motor need a guide or rail?

Yes. A linear motor creates thrust but does not support the load or hold the gap between coil and magnets, so the axis needs a linear rail or hydrostatic guideway. A linear guide only supports and directs a load, so it is not the same thing as a linear motor.

What is the difference between a linear motor and a linear actuator?

A linear actuator is usually a complete unit in which a rotary motor drives a screw or belt. A linear motor is the direct-drive thrust element alone, and the builder supplies the guide, encoder and drive. Some actuators use linear motors inside, which blurs the line.

Linear motor vs ball screw: which is better for a CNC machine?

It depends on the application. Linear motors suit high acceleration and smooth, wear-free drive. Ball screws suit long strokes, high thrust and holding loads without power, usually at lower cost. Compare both against your travel, dynamics, thermal limits and budget before deciding.

Do linear motors need cooling?

Often, yes. Coils generate heat that can transfer into the machine structure and affect accuracy. Lightly loaded axes may manage with natural convection, while demanding duty cycles typically use water-cooled motors or other thermal management to keep the axis stable during long runs.

How much does a linear motor cost?

Cost depends on thrust, stroke length, cooling and the encoder, drive and guide you add. The motor is only part of the axis budget, and longer strokes need more magnet track. The main drivers are explained under linear motor cost.