How Lead Screws Work in Micro Linear Actuators | Actuonix

What is a Lead Screw?

A lead screw simply converts rotary motion into linear motion. As the screw rotates, a nut threaded onto it travels along the shaft's length, either extending or retracting depending on the direction of spin. This is the mechanism that drives the rod in and out in every Actuonix actuator.

The diameter and thread pitch of the screw directly determine two key performance characteristics. A thicker screw with a finer pitch produces more force but moves more slowly. A thinner screw with a coarser pitch moves faster but generates less force. This trade-off is built into every actuator's design and is why Actuonix offers a range of gear ratios and lead screw configurations across its products.

What Thread Type does a Lead Screw Use?

Actuonix actuators use a metric trapezoidal lead screw thread. While the underlying geometry is similar to a trapezoidal profile that handles load across the thread face and provides inherent back-drive resistance, the metric form is optimized for the compact dimensions and force requirements of micro actuator design. The result is the same practical benefit engineers rely on: reliable linear motion, position holding without power, and long service life in a small package.

How Does a Lead Screw Work Inside a Micro Linear Actuator?

Inside a micro linear actuator, the lead screw sits along the central axis. Regardless of whether the actuator is driven by a DC motor or a stepper motor, the core mechanism is the same. The motor's rotational output turns the lead screw, either directly or through a gearbox. A nut fixed to the output rod travels along the rotating screw, converting that rotation into the linear push or pull stroke you see at the rod end.

The nut in Actuonix actuators is typically made from Delrin or a similar low-friction polymer. The sliding contact between nut and screw creates friction, and that friction is what gives the actuator its natural back-drive resistance, keeping the rod in position when power is taken off without needing a separate brake mechanism.

Do Lead Screws Experience Back-Driving?

Back-driving generally takes place when an external load pushes the rod and forces the screw to rotate in the backward direction without any input from the motor. Whether this happens comes down to the relationship between the helix angle of the thread and the friction between the screw and nut. When friction is high relative to the helix angle, the screw self-locks and stays in position. The metric trapezoidal thread used in Actuonix actuators is designed to meet this condition, which is why these actuators hold their position when power is removed without needing a brake.

What Materials are Actuonix Lead Screws made from?

The screw shaft in Actuonix actuators is typically made from stainless steel (302/304 grade) or brass, depending on the model. Stainless steel is a common choice across the Actuonix L12, L16, and P16 product lines due to its strong balance of corrosion resistance, durability, and mechanical strength. Both 302 and 304 stainless steels provide reliable performance across the range of environmental conditions these actuators are designed to operate in. Actuonix brass is RoHS-compliant and is used in certain models where different mechanical characteristics are required.

The nut, the component that threads onto the screw and drives the rod, is typically made from Delrin or a similar low-friction polymer. Delrin is an acetal resin that works well in this case because it is inherently self-lubricating, dimensionally stable, and resistant to wear over repeated cycles. It does not require any external lubrication to function, and this is the reason why Actuonix actuators come factory lubricated for the life of the unit, with no re-lubrication needed in normal use.

Can Lead Screw Actuators be Used in Harsh Environments?

Lead screws have a structural advantage in dusty or contaminated environments compared to ball screws. Ball screw assemblies rely on recirculating bearings, small rolling elements that are vulnerable to particulate contamination. If dust or debris enters the nut assembly, performance decreases rapidly. Lead screws have no rolling elements. The sliding nut contact is far more tolerant of environmental exposure.

For applications where liquid ingress is also a concern, Actuonix actuators are available with IP ratings of IP44 or IP54, depending on the model selected, providing certified protection against dust and water splash. Understand the numbers in IP rating here. For higher IP protection, the actuators can be placed in a waterproof enclosure.

Can a Lead Screw Bend?

Yes, under compressive load, a lead screw can buckle in a manner similar to a slender column subjected to an axial force. The likelihood of buckling increases with screw length and decreases with screw diameter.

In Actuonix micro linear actuators, this is rarely a practical concern because of the additional support from the extension tube and guide, and because the screw lengths are relatively short. However, it is still important to operate within the manufacturer’s specified load limits.