Ball screw lubrication normally refers to applying grease or oil to the contact area between the screw shaft, recirculating balls and ball nut raceways. The support bearings at the machined ends of the screw are separate components and may be pre-greased, sealed or lubricated according to a different maintenance schedule.
Before adding lubricant, identify which component requires maintenance. Using the wrong lubricant, mixing incompatible greases or overfilling a nut or bearing can increase running resistance, temperature and contamination risk.
Ball Screw Lubrication vs. Support Bearing Lubrication
| Component | Lubricated Contact | Common Method |
|---|---|---|
| Ball screw and nut | Balls, screw raceway and nut raceway | Grease through the nut fitting or oil supplied to the nut |
| Fixed-side support bearing | Angular-contact bearing rolling elements and raceways | Usually factory grease; follow the support-unit specification |
| Floated-side support bearing | Radial bearing rolling elements and raceways | Often factory grease or sealed-for-life construction |
Important: A grease fitting on the ball nut supplies lubricant to the ball screw raceways. It does not automatically lubricate the bearings inside the fixed-side or floated-side support unit.
Why Ball Screw Lubrication Is Necessary
Although rolling contact produces less friction than sliding contact, the balls and raceways still require a stable lubricant film. Correct lubrication helps:
- Reduce friction between the balls and raceways
- Limit wear and surface damage
- Reduce abnormal heat generation
- Support smoother ball circulation
- Protect metal surfaces against corrosion
- Carry small wear particles away from the contact area
Lubricant cannot correct poor alignment, excessive preload, damaged raceways or contamination. If the screw remains noisy or hot after lubrication, the complete installation should be inspected.
Grease or Oil: Which Should You Use?
Grease Lubrication
Grease is widely used in general CNC machines, automation equipment, linear modules and intermittent-motion systems. It is easier to retain inside the nut and normally requires less external piping than an oil system.
Select grease according to the ball screw manufacturer's recommendation and the actual speed, load, temperature and environment. General-purpose grease may not be suitable for high-speed, high-temperature, clean-room, vacuum or food-processing applications.
Oil Lubrication
Oil may be used when the machine already has a centralized oil supply or when continuous lubricant delivery and heat control are required. Oil reaches the raceway more frequently but requires suitable piping, metering and leakage management.
The oil supply position must allow lubricant to reach the loaded raceways. Mounting direction, nut orientation, stroke and oil-port position can affect distribution.
Do Not Mix Lubricants Without Checking Compatibility
Greases with different base oils, thickeners or additives may not be compatible. Mixing them can change consistency, reduce lubrication performance or cause separation.
When the existing lubricant cannot be identified, consult the original product documentation before changing to another type. Do not flush a ball nut with solvent unless an approved cleaning and relubrication procedure is available.
How to Apply Grease to a Ball Screw Nut
- Stop and secure the machine. Isolate the drive system and prevent unintended movement before maintenance.
- Check the product instructions. Confirm the recommended grease, grease point and approximate replenishment requirement.
- Clean the surrounding area. Remove dust, chips and old grease from the nipple and exposed screw surface before connecting the grease gun.
- Use a clean grease gun. Make sure it contains the correct lubricant and has not been contaminated by another grease.
- Add grease gradually. Apply the specified amount through the nut fitting without using excessive pressure.
- Move the nut through its stroke. Run the axis slowly several times so the lubricant can spread along the ball tracks.
- Inspect the motion. Check for abnormal resistance, temperature, noise or grease leakage.
- Remove excess grease. Wipe surplus lubricant from the exposed screw because it can attract dust and machining debris.
Do not place large amounts of grease directly on the exposed screw shaft and assume it will reach the complete loaded zone. Supplying lubricant through the designed nut port usually provides more controlled delivery.
How Much Grease Should Be Added?
There is no single grease quantity suitable for every ball screw. The required amount depends on nut size, internal free space, stroke, speed, mounting direction and lubricant-delivery structure.
Too little lubricant can allow metal contact, wear and heat generation. Too much lubricant can increase churning resistance, starting torque and operating temperature.
Use the value supplied with the ball screw or lubrication system. If no value is available, ask the manufacturer according to the complete ball screw model rather than estimating from the screw diameter alone.
How Often Should a Ball Screw Be Relubricated?
Relubrication intervals should be based on the manufacturer's guidance and adjusted after observing the actual machine. Travel distance and operating time can both be used as maintenance triggers.
Shorten the interval when the ball screw operates under:
- High speed or frequent acceleration
- High load or continuous operation
- Short repeated strokes that limit lubricant redistribution
- High operating temperature
- Dust, chips, coolant or moisture exposure
- Vertical, inclined or overhead mounting
As a general reference-not a universal rule-some ball screw manufacturers publish an initial guideline based on approximately six months or a specified accumulated travel distance. The final interval and amount must be established from the actual operating condition.
How Are Ball Screw Support Bearings Lubricated?
Fixed-side ball screw support units commonly use angular-contact bearings to position the screw axially. The floated side normally uses a radial bearing to support the opposite shaft end.
Many standard BK/BF, FK/FF and EK/EF support units are supplied with grease already inside their bearings. Sealed or enclosed units may not require routine grease injection during normal use.
Do not dismantle a factory-assembled fixed-side unit or add grease simply because the ball nut requires relubrication. Excess grease can increase bearing temperature, and disassembly may disturb the original bearing arrangement or preload.
If a support bearing must be replaced or repacked, follow the bearing and support-unit instructions for:
- Specified grease type
- Internal grease filling amount
- Bearing orientation and arrangement
- Lock-nut tightening procedure
- Seal installation
- Required bearing preload
DLY supplies BK/BF, EK/EF and FK/FF ball screw support units for different mounting structures and machined shaft ends.
Common Lubrication Mistakes
- Treating the ball nut and support bearings as one lubrication point
- Mixing greases without checking compatibility
- Applying grease through a dirty nipple
- Overfilling the ball nut or support bearing
- Using exposed grease that has collected dust or metal chips
- Waiting until the ball screw becomes noisy or rough before inspection
- Ignoring lubrication distribution in vertical installations
- Using a fixed maintenance interval for every machine condition
- Attempting to solve alignment or preload problems by adding more grease
Signs That Lubrication Needs Attention
Inspect the ball screw and lubrication system if you observe:
- Increasing running noise
- Higher motor torque or current
- Rough or uneven movement
- Abnormal nut or support-unit temperature
- Dry-looking raceways
- Discolored, hardened or contaminated grease
- Oil leakage or blocked lubrication piping
These symptoms do not always mean that more lubricant is required. Contamination, seal damage, poor alignment, incorrect preload or raceway damage can produce similar symptoms.
Conclusion
Ball screw lubrication and support-bearing lubrication should be treated separately. Grease is common for general ball screw applications, while oil may be used with a suitable centralized system or under operating conditions that require continuous supply.
Use the lubricant type, quantity and interval specified for the complete product. Keep lubrication tools clean, avoid mixing incompatible grease, distribute fresh lubricant by moving the axis slowly and do not open factory-prelubricated support units without a maintenance requirement.
Need help with ball screw or support-unit selection?
Send DLY the ball screw model, support-unit model, operating speed, load and working environment. We can help confirm suitable components and maintenance information.
