In engineering and mechanical design, selecting the right ball screw is critical to ensuring the precision, efficiency, and reliability of mechanical systems, from general machinery to high-precision CNC equipment. As a core component converting rotational motion into low-friction linear motion, its parameters—nominal diameter, lead, precision, etc.—directly determine load capacity, motion speed, and positioning accuracy. This guide dissects key selection criteria to help engineers optimize design solutions.
The nominal diameter refers to the outer diameter of the screw, with common specifications ranging from 12mm to 120mm. Manufacturers typically stock diameters between 16mm and 50mm; other sizes require customization (lead time: 30–60 days). Diameter correlates positively with load capacity—larger diameters suit heavy-load applications. Recommend prioritizing 16–63mm to balance versatility and delivery efficiency; consult manufacturer load tables for specific values.
The lead (pitch) denotes the linear distance the nut travels per full screw rotation, with common values of 1–40mm. Stock products often use 5mm or 10mm leads; larger leads (e.g., 1616, 2020) require customization. A larger lead enables higher linear speeds (e.g., 10mm lead for faster motion) but may compromise precision. For general applications, 5mm or 10mm leads are recommended, offering a balance of speed and control accuracy.
Distinguish between total length and thread length:
- Thread length = effective stroke + nut length + design margin (including bellows compression length, estimated as 1/8 of maximum bellows length).
- Total length = thread length + end-support length (bearing width + locknut width + margin) + power-connection length (half coupling length + margin for couplings).
Note: For lengths >3m or length-to-diameter ratios >70, consult the manufacturer in advance (domestic standard max: 3m, special: 16m; international standard max: 6m, special: 22m). For lengths exceeding 6m, rack-and-pinion systems are more cost-effective to avoid bending risks.
Nuts differ in flange type (round/single-dovetail/double-dovetail/flangeless) and single/double nut configurations:
- Single nuts: Compact, no preload adjustment, suitable for general loads.
- Double nuts: Allow preload adjustment for higher rigidity, with price and length ~2x that of single nuts—ideal for high-precision or frequent-motion applications.
Recommendation: Prioritize single nuts with double-dovetail flanges for universal use; choose double nuts for high-precision scenarios to facilitate maintenance and rigidity.
- Domestic standards (GB): Divided into transmission (T-class) and positioning (P-class), with precision grades 1–4 (Grade 1 highest).
- International standards: Class C0–C10 (C0 highest). Select C7 (positioning error ±0.05mm over 300mm travel) for general machinery, C5 (±0.018mm) for high-precision CNC, and C3+ for optical/inspection equipment.
Note: Precision correlates strongly with cost. System accuracy depends on manufacturer process reliability, not just factory-rated precision, as assembly and maintenance impact long-term performance.
The suffix in model numbers (e.g., 4010-4) indicates ball circuits. A higher number signifies greater load capacity but longer nut length. Users need not delve into circulation mechanisms; simply reference manufacturer selection tables based on load requirements.
The ball diameter (precise to 0.001mm) is listed in technical parameter tables but is irrelevant for normal use. It becomes crucial only if balls dislodge and require reinstallation, necessitating exact matching.
- Rolled (F-type): Mass-produced, high efficiency, low cost, with max precision up to C5 (rarely achievable by some manufacturers).
- Ground (G-type): Precision-machined for higher accuracy (C5+), lower equipment threshold but lower production efficiency.
Recommendation: Choose rolled screws for the same precision class, as they offer better cost-effectiveness. Nuts are always ground, regardless of screw process.
Preload levels determine the tightness between the nut and screw: higher levels suit large diameters, double nuts, high torque, or rigid requirements; lower levels are for light loads or minimal friction. Follow manufacturer-recommended parameters—no need to calculate values independently.
- Stock vs. Customization: Prioritize standard sizes (16–50mm diameter, 5/10mm lead) to reduce lead times; allow 30–60 days for custom specifications.
- Length-to-Diameter Ratio Control: Confirm feasibility with manufacturers for lengths >3m or ratios >70 to avoid vibration from insufficient rigidity.
- System-Wide Matching: Integrate motor power, load characteristics (dynamic/static), and environmental factors (dust/temperature). Use manufacturer selection software or formulas to validate designs.
Selecting a ball screw is a multi-parameter engineering task requiring optimization among load, speed, precision, and cost. Engineers should focus on core parameters like nominal diameter, lead, and precision, while leveraging manufacturer technical support and inventory capabilities to avoid over-engineering or performance shortfalls. By combining standardized selection with rational preload and process choices, mechanical system reliability and service life can be significantly enhanced, laying the foundation for precise motion control in high-end equipment.
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