Ball screws are widely used on horizontal machine axes because their rolling contact provides efficient transmission, smooth movement and accurate positioning. However, the main advantage of a horizontal arrangement is not that the ball nut supports the weight of the moving table. The table weight should be carried by linear guideways, while the ball screw and ball nut provide axial driving force.
Compared with a vertical axis, a correctly designed horizontal axis normally does not require the ball screw to continuously lift the moving mass against gravity. This can reduce the continuous drive force, holding requirement and risk of uncontrolled downward movement. The actual motor and ball screw size must still be calculated from acceleration, friction, external process force, stroke, speed and duty cycle.
Contents
- How Loads Should Be Distributed on a Horizontal Axis
- Main Advantages of a Horizontal Ball Screw Axis
- Horizontal vs. Vertical Ball Screw Axes
- How to Estimate the Required Driving Force
- Choosing the Right Ball Nut
- Horizontal Installation Checks
- Common Design Mistakes
- DLY Ball Screw and Nut Options
- FAQ
How Loads Should Be Distributed on a Horizontal Axis
A horizontal linear axis normally combines a ball screw with one or more linear guideways. These components perform different functions.
| Component | Main function | Loads it should carry |
|---|---|---|
| Linear guideways and blocks | Guide and support the moving table | Table weight, radial load, pitch moment, yaw moment and roll moment |
| Ball screw and ball nut | Convert motor rotation into linear movement | Axial acceleration force, guide friction and external process force along the screw axis |
| Fixed-side support bearing | Locate the screw axially and support thrust load | Axial reaction and part of the screw-support load according to the bearing arrangement |
| Supported-side bearing | Support the opposite screw end | Radial support while allowing the intended axial arrangement |
If the ball nut housing is used to carry table weight or correct guideway misalignment, the nut receives an unintended radial or moment load. This can create uneven ball contact, high running torque and premature raceway wear.
The ball nut flange connects the nut to the moving table or nut housing, while the linear guideways support the table weight.
Main Advantages of a Horizontal Ball Screw Axis
Gravity does not continuously oppose horizontal travel
On a level horizontal axis, gravity acts downward and is carried mainly by the linear guideways. It does not normally create a continuous axial force along the ball screw. The drive must overcome guide friction, acceleration force and external working force, but it does not continuously lift the full moving mass.
This differs from a vertical axis, where gravity creates a continuous axial load and can cause the table to move downward if the motor, brake or counterbalance cannot hold it.
Lower holding-force requirement at standstill
A horizontal axis with no external axial force may require relatively little drive torque to remain stationary. A vertical axis normally needs a motor brake, counterbalance or another holding device because ball screws can back-drive.
This does not mean every horizontal axis can remain stationary without a brake. An inclined installation, spring force, pneumatic cylinder, cutting force or another external load may still drive the axis when power is removed.
Efficient acceleration and positioning
The rolling contact between the balls and raceways gives a ball screw lower mechanical friction than a conventional sliding lead screw. On a horizontal axis, this can support efficient acceleration and repeated positioning when the diameter, lead, preload, motor and support arrangement are selected correctly.
A smaller motor must not be selected from efficiency alone. The motor also needs sufficient acceleration torque, peak torque, speed and safety margin for the complete moving mass and process load.
Easier lubrication distribution than some vertical layouts
In a horizontal arrangement, grease is less likely to migrate consistently toward one end only because of gravity. However, lubrication still needs to reach all loaded raceways and ball-return paths. Long stroke, high speed, contamination and limited access may require a centralized lubrication system.
No uncontrolled gravity drop in a truly level axis
A horizontal axis does not normally fall under its own weight when drive power is lost. This reduces one of the important safety risks associated with vertical ball screw systems. Stored energy and external forces still need to be considered during machine risk assessment.
Horizontal vs. Vertical Ball Screw Axes
| Selection point | Horizontal axis | Vertical axis |
|---|---|---|
| Effect of moving mass | Weight is mainly supported by linear guideways | Weight creates a continuous axial load along the screw |
| Holding at standstill | Often lower holding-force requirement if no external axial force exists | Usually requires a brake, counterbalance or another safety measure |
| Back-driving risk | Normally does not cause gravity-driven travel on a level axis | Load may descend when holding torque is removed |
| Primary force calculation | Acceleration, guide friction and process force | Acceleration, gravity, friction and process force |
| Lubrication | Distribution must be checked across the stroke | Lubricant migration and access may require additional attention |
| Safety focus | End stops, collision forces and stored external energy | Uncontrolled descent, brake capacity and load holding |
How to Estimate the Required Driving Force
For a simplified horizontal axis, the required axial driving force can be estimated as:
The acceleration force is:
Where:
- m is the total moving mass, including the table, workpiece, fixture and moving machine components.
- a is the required linear acceleration.
- Ffriction is the resistance from guideways, seals, covers and other moving parts.
- Fprocess is the cutting, pressing, clamping or external working force acting along the axis.
- Fother includes cable-chain resistance, bellows resistance, spring force and other external effects.
This simplified force is used together with the screw lead and transmission efficiency to estimate drive torque. Motor selection must also check acceleration time, motor inertia, screw inertia, maximum speed and required safety margin.
For an inclined axis, include the component of gravity acting along the screw:
Therefore, an axis that appears almost horizontal may still require holding-force and back-driving checks if the installation angle is not zero.
Choosing the Right Ball Nut
The installation direction alone does not determine the correct nut. Select the ball nut together with the screw shaft according to the actual motion requirements.
| Selection item | Why it matters |
|---|---|
| Axial load | Used to check dynamic and static load ratings and expected fatigue life |
| Screw diameter | Affects strength, rigidity, allowable speed and buckling resistance under compression |
| Lead | Affects linear travel per revolution, speed, motor torque and positioning resolution |
| Nut type | Determines flange dimensions, installation space, load rating and circulation structure |
| Axial clearance or preload | Affects reversal accuracy, rigidity, running torque and heat |
| Accuracy grade | Selected from permissible lead error and positioning requirement |
| Mounting dimensions | The flange, bolt circle, nut body and housing must fit the machine structure |
A preloaded or double-nut design may be considered when greater axial rigidity or reduced backlash is required. It should not be selected automatically because additional preload also increases torque and heat.
Horizontal Installation Checks
Align the screw with the guideway travel
The ball screw axis should follow the established direction of the linear guideways. Do not use the ball nut housing or coupling to pull a misaligned screw into position.
Support long screws correctly
Horizontal screws can deflect under their own weight, especially when the screw is long and relatively small in diameter. Check screw length, diameter, support arrangement, operating speed and critical speed rather than assuming a horizontal installation prevents bending.
Keep radial load away from the ball nut
The nut housing should transfer axial force without forcing the ball nut to compensate for an incorrectly positioned table. Mounting faces should be clean and correctly aligned before the flange bolts are fully tightened.
Check compression and tension directions
A ball screw loaded in compression must be checked for buckling. The risk depends on unsupported length, root diameter, support arrangement and axial force. Where possible, the machine layout may be arranged so that the main working force places the screw in tension, but the complete bidirectional load cycle must be reviewed.
Provide covers and lubrication access
Horizontal raceways can collect chips, dust and process residue along their exposed length. Bellows or covers should be considered, and the lubrication port must remain accessible after the table and nut housing are assembled.
Common Design Mistakes
- Allowing the ball screw to guide the moving table without suitable linear guideways.
- Treating the ball nut's load rating as permission to apply radial or moment load.
- Selecting the motor from table weight alone and ignoring acceleration or process force.
- Assuming a horizontal axis can never back-drive, even when it is inclined or externally loaded.
- Ignoring long-screw sag, critical speed or compression buckling.
- Choosing maximum preload without checking running torque and heat.
- Using the coupling to correct substantial screw-to-motor misalignment.
- Mounting the ball nut rigidly before establishing guideway and screw alignment.
- Leaving the screw exposed to chips because the installation is horizontal.
DLY Ball Screw and Nut Options
DLY supplies separate ball nuts and complete matched ball screw assemblies. Common ball screw options include rolled C7 and C10 and ground C5, C3 or C0 according to the required specification. The screw shaft material is S55C, and the ball nut material is 20CrMo.
Available supply and processing support includes:
- SFU, DFU, SFNU, SFE and other confirmed nut structures.
- Separate replacement ball nuts or matched screw-and-nut assemblies.
- Common leads such as 4mm, 5mm and 10mm, with SFE options for high-lead applications.
- Customized total length up to 6 metres where manufacturing and transportation conditions permit.
- BK/BF, FK/FF and EK/EF shaft-end machining.
- Drawing-based custom end machining.
View the DLY recirculating ball nut range or learn how to choose the right ball screw diameter.
FAQ
Does the ball nut support the weight of a horizontal table?
No. The linear guideways should support the table weight, radial loads and moments. The ball nut should primarily transfer axial force along the screw.
Does a horizontal ball screw need a motor brake?
Not always. A level axis without an external axial force does not normally descend under gravity. A brake may still be required for safety, precise holding, inclined installation or external forces.
Can horizontal installation prevent ball screw sag?
No. A long horizontal screw can deflect under its own weight. Diameter, length, supports, speed and permissible runout must be checked.
Is a preloaded ball nut necessary on every horizontal axis?
No. Preload may improve axial rigidity and reversal performance, but it also increases running torque and heat. Select it according to the actual positioning and rigidity requirement.
Can I replace only the ball nut?
Possibly, if the replacement nut matches the screw diameter, lead, thread direction and circulation structure and the existing screw raceway remains in good condition. A seriously worn, rusted or damaged shaft may require a complete matched assembly.
Contact DLY
Send us the moving mass, speed, acceleration, stroke, external axial load, required accuracy, ball nut type and shaft-end drawing for model confirmation and quotation.
Email: dlyexport2@dlybearing.com | WhatsApp: +86 166 0578 8856
