SFK Ball Screw

The SFK ball screw is a miniature ball screw series designed for compact linear positioning mechanisms. Its internally recirculating ball system eliminates the external return tube used on many conventional ball screw nuts, allowing the SFK nut to retain a compact flanged profile.

DLY supplies standard SFK models with screw diameters from 4 mm to 16 mm. Available leads range from 1 mm to 4 mm according to the selected diameter. The standard configuration is a C7 rolled ball screw, while C5 ground accuracy can be confirmed for applications with higher positioning requirements.

SFK Ball Screw Structure

SFK uses a compact flanged single nut with internal ball recirculation. Compared with larger external-circulation ball screw nuts, this structure requires less radial installation space and is better suited to miniature linear modules and small positioning assemblies.

• Compact nut: Internal recirculation avoids an external return tube.
• Small screw diameters: Standard models start from a 4 mm nominal diameter.
• Fine lead options: Selected models are available with 1 mm, 2 mm or 2.5 mm leads for controlled linear feed.
• Flanged mounting: The nut flange provides a defined mounting interface for compact assemblies.

SFK Model Number

An SFK model number identifies the nominal screw diameter and lead. For example, SFK0802 represents an 8 mm screw diameter with a 2 mm lead. This does not mean that every diameter is available with every lead; the standard combinations are shown in the specification table below.

Dimensions are in millimetres. Ca and Coa are stated in kgf; stiffness K is stated in kgf/μm. Load ratings should be used together with operating speed, stroke, duty cycle and required service life when selecting a model.

How to Select an SFK Model

Begin with the screw diameter permitted by the installation space and required load. Then select the lead according to the required travel per revolution:

• 1 mm lead: SFK0401, SFK0601 and SFK0801.
• 2 mm lead: SFK0802, SFK1002, SFK1202, SFK1402 and SFK1602.
• 2.5 mm lead: SFK0802.5.
• 4 mm lead: SFK1004.

A smaller lead produces less linear travel per motor revolution and can provide finer theoretical positioning resolution. A larger lead provides more linear travel per revolution but changes the required motor speed and driving torque. Final selection should therefore consider lead, load rating, speed and the complete drive system together.

Accuracy and Materials

• Standard type: C7 rolled miniature ball screw.
• Optional type: C5 ground ball screw, subject to model confirmation.
• Screw shaft material: S55C.
• Ball nut material: 20CrMo.
• Thread direction: Right-hand thread is standard.

The 4 mm and 6 mm SFK nuts are supplied without seals. DLY standard SFK nuts are generally unsealed, so the operating environment and lubrication arrangement should be considered when the screw will be exposed to dust or other contaminants.

Typical Applications

The small screw diameters, fine lead combinations and compact flanged nut make SFK ball screws suitable for miniature linear modules, small measuring devices, laboratory equipment, optical positioning mechanisms and other compact automation assemblies.

For larger screw diameters or higher-load machine axes, view DLY's ball screw series to compare other nut structures and diameter ranges.