SFJ00808-1.8 Ball Screw (Shaft ⌀8 mm, Lead 8 mm, Precision-ground)

SFJ00808-1.8 — Mounting & Lock-nut Torque (reference)

The values below are general references for precision lock nuts. Always follow the manufacturer's technical manual; tighten the lock nut symmetrically and step-by-step to avoid eccentric preload.

Lock nut thread	Reference torque
M10	18 N·m
M12	28 N·m
M14	38 N·m
M15	46 N·m
M16	55 N·m
M20	95 N·m
M25	180 N·m
M32	340 N·m
M40	620 N·m

For this model the shaft is 8 mm, the lock nut thread is approx. M10, and the recommended reference torque is approx. 18 N·m. Apply the same rule to the support-unit bearing lock nut per the matching shaft diameter.

SFJ00808-1.8 — Load & Accuracy Match

• Dynamic load rating Ca = 89 kgf; use under an equivalent axial load ≤ Ca/3 (approx. 30 kgf) for long fatigue life; short peaks should not exceed Ca long term.
• Static load rating Coa = 164 kgf; in static or low-speed positioning the max axial force should stay below this to avoid permanent deformation.
• Precision grade: Precision-ground — This is a high-precision grade (typically C3 / C5), with high positioning accuracy and small backlash, suited to semiconductor equipment, measuring instruments, CNC machining centers and other high-accuracy applications.
• Circulation type: End-cap circulation · silent reinforced dust-proof. Axial rigidity 5 kgf/µm — higher rigidity means better positioning stiffness and load-deformation resistance; double-nut preload further raises rigidity but also friction torque.
• Lead 8 mm — Medium lead — balances speed and thrust, the most versatile choice for most automation feed scenarios.

SFJ00808-1.8 — Common Faults & Troubleshooting

Symptom	Possible cause	Check & remedy
Noise / abnormal sound	insufficient lubrication, foreign matter in circuit, over-preload, damaged support bearing	re-lubricate, clean & shield, re-check preload, replace support bearing
Loss of accuracy / increased backlash	nut preload loosened, screw worn, support bearing clearance, coupling loose	re-tighten lock nut per table, check support unit, re-align coupling concentricity
Sticking / crawling	rail-screw parallelism out of tolerance, poor lube, overload beyond Ca	re-check parallelism & concentricity, improve lubrication, verify load within rating
Overheating	over-preload, speed over DN limit, lube failure	reduce preload, control speed, use high-temp grease
Rust / pitting	high humidity, coolant ingress, no anti-rust care	add telescopic cover, use stainless/coated screw, periodic anti-rust

For this model, shaft ⌀ 8 mm and lead 8 mm — at high speed watch the DN value (shaft dia mm × rpm); exceeding the manufacturer's limit causes heat and noise.

SFJ00808-1.8 — Typical Applications

Thanks to its precision-ground accuracy, the SFJ series is widely used in semiconductor equipment, measuring instruments, CNC machining centers and laser processing where positioning accuracy is critical.

SFJ00808-1.8 — Installation & Maintenance

• Pre-stretch: for long-stroke screws apply axial pre-stretch per the manufacturer's coefficient to compensate thermal drift.
• Lubrication: re-grease every 500–1000 running hours; shorten the interval and use the right grade for high speed or clean rooms.
• Protection: use telescopic covers / wipers to keep chips and dust out of the nut circuit.
• Concentricity: keep screw-to-rail parallelism ≤ 0.02 mm/m; the support mounting face must be flat.
• Tightening: tighten the lock nut symmetrically and step-by-step per the table above.