Double Ball Nut for Preloaded Ball Screw Systems
DLY Double Ball Nut is used in ball screw systems where reverse movement, axial rigidity and repeat positioning stability are more important than a simple low-friction feed. Compared with a single nut, the double nut structure uses two ball nut sections to create controlled preload, helping reduce axial clearance and improve stiffness during repeated forward and backward movement.
This design is commonly selected for CNC feed axes, precision automation equipment, measuring mechanisms, grinding machines and other systems where backlash cannot be ignored. Before quotation, DLY checks the screw diameter, lead, nut length, preload method, flange dimensions and available installation space, so the double ball nut can match the real machine structure instead of only matching a model name.
What Makes a Double Ball Nut Different?
A normal ball nut mainly focuses on smooth transmission. A double ball nut goes one step further: it uses two nut sections on the same screw shaft to create an opposing load between the nuts. This preload helps remove part of the axial clearance between the screw groove and the balls.
In real machine operation, the difference becomes obvious when the axis changes direction. If the nut has too much axial play, the machine may hesitate slightly before movement transfers to the table or slide. A properly matched double ball nut can reduce this lost motion and improve repeatability in forward and reverse travel.
This is why double ball nuts are more often used on positioning axes, feed systems and machines that require stable cutting, measuring or repeated motion. They are not chosen only for load capacity, but for the balance between preload, rigidity, running torque and service life.
How Double Nut Preload Works
The key value of a double ball nut is preload. In many designs, the preload is created by adjusting the relative position of two nut sections. This can be done by spacer adjustment, thread adjustment or a structure designed for controlled axial offset.
Axial Clearance Reduction
Preload pushes the two nut sections against opposite sides of the screw groove, reducing the free axial movement that may appear when direction changes.
Rigidity Improvement
A preloaded nut pair gives the screw system stronger axial support, which is useful when the machine axis carries cutting force, workpiece load or repeated impact.
Running Torque Control
More preload is not always better. Excessive preload can increase torque, heat and wear. DLY checks preload requirements according to real working conditions.
Double Ball Nut Selection Guide
Choosing a double ball nut is different from choosing a standard replacement nut. The buyer needs to check not only the screw model, but also the preload target, available nut length, installation direction and the machine's tolerance for running torque.
| Selection Point | Why It Matters | What DLY Checks |
|---|---|---|
| Screw Diameter and Lead | The double nut must match the screw raceway exactly. | Diameter, lead, thread direction and whether the screw is standard or customized. |
| Preload Level | Preload affects backlash, torque, heat and service life. | Light preload for smooth feed, higher preload for rigidity-sensitive axes. |
| Nut Length | Double nuts are longer than single nuts and may not fit compact machines. | Total nut length, available travel and interference with support parts. |
| Mounting Structure | Flange position and hole pattern affect direct replacement. | Flange OD, PCD, mounting hole size and bracket compatibility. |
| Machine Axis Requirement | Not every axis needs a double nut. | Whether the axis needs backlash control, load support, or only general movement. |
Where a Double Ball Nut Performs Better
The value of a double ball nut is most obvious on axes that frequently change direction or need stable repeat positioning. It is not only a stronger nut, but a preload solution for more controlled linear movement.
Z Axis with Load Holding
Useful when the axis carries vertical load and needs more stable support during lifting, lowering or positioning.
CNC Feed Axis
Helps improve response during direction changes, especially when cutting force and reverse movement affect machining consistency.
Inspection and Measuring Equipment
Suitable for mechanisms that need repeated positioning stability rather than only high travel speed.
Precision Automation Module
Used in automatic feeding, alignment or adjustment structures where axial looseness may affect final assembly quality.
What DLY Checks Before Supplying a Double Ball Nut
Instead of only matching a catalog name, DLY checks several practical details that affect whether the double nut can run correctly after installation. This helps buyers reduce the risk of tight running, insufficient preload or wrong mounting dimensions.
Preload Direction
We check how the two nut sections should be positioned so the preload works in the intended axial direction.
Nut Running Feel
For preloaded nuts, smooth movement and controlled resistance should be balanced. The nut should not feel loose, but it should not be excessively tight.
Assembly Clearance
Double nuts require more axial space. DLY helps buyers check whether the nut length will affect stroke, support blocks or coupling position.
Double Ball Nut vs. Single Ball Nut
A double ball nut is not always necessary. For many low-load or non-positioning applications, a single nut is simpler and more economical. The double nut is mainly selected when the machine needs better control over axial play.
| Comparison | Single Ball Nut | Double Ball Nut |
|---|---|---|
| Structure | One nut body, compact design. | Two nut sections or double-nut structure. |
| Backlash Control | Suitable for general motion requirements. | Better for applications requiring reduced axial play. |
| Installation Space | Shorter and easier to fit. | Longer, requires more axial room. |
| Running Torque | Usually lighter. | Depends on preload level and assembly condition. |
| Recommended Use | General automation, simple feed axes. | CNC axes, precision feed, load-holding and backlash-sensitive systems. |
Details to Send Before Quotation
Double ball nuts are more sensitive to matching than standard nuts. To avoid wrong preload or installation problems, please send as many of the following details as possible.
Existing Model or Drawing
Send the old nut model, drawing, or clear photos from different sides if the model is not visible.
Screw Shaft Information
Confirm screw diameter, lead, thread direction, total screw length and whether the screw shaft will also be supplied.
Required Motion Condition
Tell us whether the machine needs low backlash, high rigidity, smooth high-speed motion or general replacement.
Installation Space
Provide available axial space, flange mounting dimensions and any nearby support block or coupling limitations.
FAQ About Double Ball Nuts
Q1: Does a double ball nut always have zero backlash?
Not always. A double ball nut is designed to reduce axial clearance through preload, but the final result depends on screw condition, preload level, assembly accuracy and working load.
Q2: Will higher preload always improve accuracy?
No. Excessive preload can increase running torque, heat and wear. The suitable preload should match the machine's rigidity and motion requirement.
Q3: Can I replace a single nut with a double ball nut?
It depends on the screw shaft and available installation space. A double nut is usually longer than a single nut, so the machine stroke and mounting structure must be checked first.
Q4: What causes a preloaded double nut to feel too tight?
Possible reasons include excessive preload, wrong screw matching, raceway wear, contamination, poor lubrication or installation misalignment.
Q5: Should I replace the screw shaft together with the double nut?
If the screw raceway is worn, rusted or scratched, a new double nut may not run correctly on the old shaft. In this case, a matched ball screw and double nut assembly is safer.
Get Double Ball Nut Price from DLY
Send us the screw diameter, lead, nut drawing, preload requirement, machine axis type and quantity. DLY will help check whether a double ball nut is suitable for your application and whether the nut should be supplied alone or matched with a ball screw shaft.
Email: dlyexport2@dlybearing.com
WhatsApp: +86 16605788856
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