How to Adjust Large-Lead Ball Screw Nut Clearance—When Possible

The clearance between a large-lead ball screw and its nut cannot always be adjusted in the machine. Whether adjustment is possible depends on the nut structure and how its preload was originally established.

Most standard single ball nuts have factory-controlled axial clearance or preload. Tightening the nut housing, moving the nut to another position on the screw or adding shims under the mounting flange does not change the internal contact between the balls and raceways.

What Clearance Are You Measuring?

Before attempting an adjustment, determine where the lost motion originates. Movement measured at the machine table is not automatically the internal clearance of the ball nut.

Reversal error can come from several parts of the transmission system:

Large lead increases the linear travel produced by each screw revolution, so angular lost motion in the motor, coupling or screw may create a larger linear positioning error. However, the method used to control internal nut clearance still depends on the ball nut structure, not on the lead alone.

Axial clearance is measured as relative movement between the ball screw shaft and nut, not with a feeler gauge inserted into the raceway.

A large-lead single nut is normally supplied with factory-controlled clearance and is not automatically field-adjustable.

How to Measure Axial Clearance

A feeler gauge cannot normally measure the internal axial clearance of a recirculating ball nut. The balls are enclosed within matched helical raceways, and the required measurement is axial displacement under reversing force.

Method 1: Measure the Removed Ball Screw Assembly

1. Clean the exposed screw raceway and inspect it for dents, corrosion or obvious wear.
2. Support and secure the screw shaft without damaging the raceway.
3. Position a dial indicator against the axial face of the ball nut flange.
4. Apply a small, controlled axial force to the nut in one direction and set the indicator to zero.
5. Apply the same force in the opposite direction without rotating the screw or nut.
6. Record the total indicator movement as the measured axial play under that test force.

The test force must be controlled and appropriate for the assembly. Excessive manual force can include elastic deformation of the supports or measuring fixture and produce a misleading result.

Method 2: Diagnose the Assembly in the Machine

When the assembly remains installed, measure each connection separately. First check whether the screw shaft moves relative to the bearing housing. Then check whether the nut housing moves relative to the table. Finally evaluate movement between the screw and ball nut.

If only table movement is measured, support-bearing clearance, coupling motion, nut-housing looseness and structural deformation may all be included in the result.

For a general explanation of backlash and its possible sources, see What Is Ball Screw Backlash?

Can the Clearance Be Adjusted?

The correct method cannot be determined from the words "large lead" alone. The complete nut model, internal structure and original preload method must be identified before any adjustment.

Standard Large-Lead Single Nut

Many SFE and other high-lead ball screw models use a single flanged nut. Their internal clearance is established during manufacturing and matching. If wear has increased the clearance, there is normally no external screw or locknut that can restore the original fit.

The suitable solution is usually to inspect the screw and nut together and decide whether professional ball rematching, nut replacement or complete assembly replacement is required.

Adjustable Double-Nut Assembly

A double-nut system can use a spacer, relative nut position or spring mechanism to create axial preload. Adjustment may be possible, but only within the design range.

Increasing preload too far can cause excessive running torque, heat, noise, ball skidding and shortened fatigue life. The goal is not to make the nut as tight as possible; it is to obtain the required rigidity and reversal accuracy while maintaining smooth movement.

Adjustment Process for Adjustable Nuts

The following process applies only after confirming that the ball nut has a manufacturer-approved adjustable structure.

1. Isolate the machine. Disconnect drive power and secure vertical or suspended loads before working on the axis.
2. Identify the nut structure. Confirm the model, drawing, spacer, spring and locking mechanism.
3. Inspect external components. Check the coupling, bearing locknut, support bearings, nut housing and mounting bolts first.
4. Record the baseline. Measure axial clearance, full-stroke running torque, noise and any temperature rise before adjustment.
5. Mark the original position. Mark adjustable nuts, spacers or locking parts so the initial setting can be restored.
6. Adjust in small controlled increments. Follow the specified spacer or nut-position procedure rather than making a large change at once.
7. Secure the locking mechanism. Use the specified locking method and torque after reaching the required setting.
8. Measure again. Recheck axial clearance using the same indicator position and test force.
9. Test the complete stroke. Confirm that torque remains smooth and that there is no tight point, roughness or abnormal noise.
10. Run at reduced speed first. Monitor torque, temperature and sound before returning the machine to normal operation.

Methods That Do Not Adjust Internal Clearance

Inserting a Feeler Gauge

A feeler gauge is not suitable for measuring the internal helical contact between the balls and raceways. Axial displacement should be measured with a dial indicator under reversing force.

Moving the Nut Along the Screw

Moving a standard nut to another axial position does not change its internal clearance. If the measured play changes significantly along the screw, this may indicate localized raceway wear or damage rather than an available adjustment.

Tightening Nut-Housing Bolts

Tightening loose housing bolts can remove movement between the nut housing and machine table, but it does not reduce clearance inside the ball nut.

Adding Shims Under the Nut Flange

Shims between the nut flange and housing change mounting position or alignment. They do not change the matching relationship between the balls and the internal raceways. Incorrect shimming can tilt the nut and create misalignment.

Adding More Lubricant

Correct lubrication can improve running smoothness and reduce wear, but it cannot restore material already lost from worn balls or raceways. A temporary reduction in noise after lubrication should not be mistaken for successful clearance adjustment.

Installing Larger Balls Without Matching Data

Changing ball diameter alters preload, contact stress, running torque and ball circulation. Installing oversized replacement balls without the original ball specification and matching procedure can jam or damage the assembly.

Do not remove a ball nut from its screw without the correct transfer sleeve. The balls may fall out, and their circuit positions, quantities or size groups may be lost.

When to Repair or Replace the Assembly

Adjustment is not the correct solution when the increased clearance is caused by wear or physical damage. Professional inspection or replacement should be considered when:

• The standard single nut has no designed adjustment mechanism.
• Clearance returns quickly after a double-nut adjustment.
• The screw raceway has pitting, dents, corrosion or visible flaking.
• The nut has rough movement or tight points along the stroke.
• Metallic particles repeatedly appear in the lubricant.
• Noise and torque remain abnormal after alignment and lubrication checks.
• The ball return components or seals are damaged.
• The required clearance cannot be achieved without excessive preload and heat.

Zhejiang DLY Automation Manufacturing Co., Ltd. supplies large-lead ball screws, standard single nuts and double-nut ball screw structures. DLY can also confirm customized length, end machining and nut matching according to the model and drawing.

View the DLY large-lead ball screw page for product information.

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