Lead and ball screws are essential to the automation industry’s ability to provide appropriate linear motion control solutions. Many people believe that lead screws are only a less costly option to ball screws because they are similar and easy to mistake.
What is Ball Screw？
A ball screw is made up of a screw shaft and a ball nut with helical threads that match. These units are used to transmit forces to a dynamic or stationary load with high precision, accuracy, and repeatability. The ball nut uses recirculating bearings to transfer power from rotational motion to linear motion along the ball screw’s axis with little friction.
Learn More What is a Ball Screw? Core Structure and Working Principle Analysis
Ball screw advantages
There is no doubt that ball screws offer a multitude of superior performance characteristics compared to lead screws. They offer precision accuracy, better efficiency, higher speed, and lower friction.
- Precision Accuracy
- Low Coefficient of Friction
- Greater Efficiency
- Less Torque Requirement
- Less Heat Generation
- High-Duty Cycle Capability
- Preload Adjustable
- Higher Speed
- Longer Lifetime
Disadvantages of Ball screw
Ball screws are suitable for many applications, but there are some disadvantages to consider:
- Lubrication is Required to Maximize Lifespan
- Braking Systems are Required to Prevent Back-Driving
- Can Cause Problems in Vertical Configurations
- More Noise Generation
- More Costly than Lead Screws
Applications of Ball screws
Ball screws are best suited for applications requiring continuous or high-speed movement, precision, accuracy, efficiency, and smooth motion. Common use cases include:
- Precise positioning systems in electric vehicles and automotive steering systems
- Energy generation machinery such as solar panels, wind turbines, and hydroelectric equipment
- Aircraft machinery
- Viewing systems for photolithography processes
What is Lead Screw？
Lead screws are commonly used in applications that require a unit that won’t “back-drive,” but their designs have evolved to reduce friction. They have a sliding screw shaft and nut threads that move directly against each other on a large contact area, resulting in higher energy losses due to friction. They are ideal for light to medium-duty applications and provide silent, smooth operation.
Lead screw advantages
- Cost-Effectiveness
- Vertical Application Suitability
- Self-Locking Property
- 30-80% efficiency
- Lower cost
- Quiet – no ball recirculation
- Can operate with or without lubrication
- More compact and offer greater design flexibility
Disadvantages of Lead Screws
Although lead screws typically come at a lower price point, they come with certain drawbacks, including:
- Reduced Lifespan
- Lower Efficiency
- Low-Speed
- More Heat Generation
- Increased Friction Generation
- Require a Larger Drive and Motor
- Increased Torque Requirements
Applications of Lead Screws
Lead screws are often suitable for simple motion transfer applications that require less rigidity, precision, accuracy, and speed. Common use cases include:
- Life Sciences and Laboratory Equipment Such as Scanning and Fluid-Handling Devices
- Engraving Machinery
- Rapid Prototyping Equipment
- Inspection Equipment
- Data Storage
- Heavy Lifting Applications (when combined with a metal nut)
Ball Screws vs Lead Screws: What are the differences?
The basic difference between a lead screw and a ball screw is that a ball screw uses a ball bearing to eliminate friction between the nut and the lead screw, whereas a lead screw does not.
1. Different structure
The ball screw contains balls, whereas the screw shaft has an arc contour. This profile is hovering on the shaft at a specific lift angle (lead angle). The ball is intended to fit in the nut and roll along the screw shaft’s arc profile, resulting in rolling friction.
Because the trapezoidal screw lacks balls, sliding friction occurs when the nut and screw shaft make mechanical contact.
2. Different transmission efficiency
The coefficient of friction for rolling friction is significantly lower than that of sliding friction.
For instance, according to both NSK and THK, ball screws have a coefficient of friction between 0.003 and 0.01 while lead screws only have a coefficient between 0.1 and 0.2.
In another example, REXROTH shows that ball screws have a coefficient of friction between 0.005 and 0.01 and lead screws have a coefficient of friction between 0.2 and 0.3.
As a result, most ball screws have transmission efficiencies of up to 90%, and some even surpass 95%, whereas most lead screws have transmission efficiency of less than 70%.
3. Different self-locking
According to the hypothesis, there is no self-locking when the lead screw transmission efficiency is more than 50% and self-locking when the transmission efficiency is lower than 35%. As a result, the trapezoidal screw has a specific self-locking feature, but the ball screw does not.
The lead screw has the benefit of self-locking when it comes to Z direction applications. Naturally, in the real world, elements like speed and precision must also be taken into account.
4. Different manufacturing materials
The ball screw shaft is generally made of stainless steel or alloy steel, and the nut is generally made of copper, because copper can bear a large load, and at the same time, the friction coefficient is small, and it has a certain self-lubricating effect, just like some of our common linear bearings, or planes Skateboards, which also use copper, are exactly that reason.
Stainless steel or alloy steel are also used to make the trapezoidal lead screw shaft. It differs somewhat from ball screws for nuts. Lead screw nuts frequently make use of non-metallic materials. Examples of synthetic engineering materials that are typically used when the load is low include nylon, race steel, PEEK, VESPEL, PET, PPS, and other materials that are mixed with Teflon (PTFE) to achieve a low friction coefficient while also having some heat resistance.
5. Different applicable scenarios
The lead screw has sliding friction, and excessive speed will generate high heat on the joint surface, resulting in increased wear. Therefore, the lead screw is suitable for applications with light weight and low speed requirements. At the same time, the lead screw, because of its lower precision, is often more suitable for applications that do not require high precision, such as slow transfer, handling, etc. Ball screws, on the other hand, have low heat generation and high precision, and are generally more suitable for applications that require smooth motion, high efficiency, high precision, and long-term continuous or high-speed motion, such as semiconductor equipment.
6. Working life
The ball’s rolling friction typically has a low surface friction force. The ball screw has a longer operating life than the trapezoidal screw under the assumption of varied cleaning and maintenance procedures.
The table below draws a comparison between ball screws and lead screws.
| Characteristic | Ball Screws | Lead Screws |
| Type of Contact | Rolling (Low Friction) | Sliding (Friction) |
| Efficiency | Higher | Lower |
| Backlash | Typically lower | Typically higher |
| Precision | High | Moderate |
| Load Capacity | Higher | Lower |
| Axial Play | Less | More |
| Maintenance | Generally Lubrication-Free | Requires Lubrication |
| Speed | Typically Higher | Typically Lower |
| Cost | More Expensive | More Economical |
| Noise | Quieter | Louder |
| Application Range | High-Precision | General Purpose |
6 Factors Choose Right Ball Screw Or Lead Screw
1.Motion Profile
Ball screws should be considered first for applications with high speeds or loads (more than 100 pounds). Their multi-ball design provides increased surface contact, allowing them to handle heavier loads faster while maintaining higher application speeds during a continuous duty cycle.
Lead screws have a modest advantage in applications requiring lower speeds or loads. This is also true for vertical applications, where lead screws can self-lock and counteract gravity.
2.Efficiency
Lead screws typically have an efficiency of 30–70%, but ball screws have an efficiency of 85–95%. This is because ball screws have a lower coefficient of friction than sliding contacts.
Because of this boost in efficiency, ball screw applications may need to take overhung loads or high inertia brakes into account.
3.Accuracy
The possible variance in travel distance within a given screw length is known as accuracy. Numerous elements, such as diameter, stroke, manufacture method, and measuring scale, are expressed in it.
Although efficiency is a more important factor in separating ball screws from lead screws than accuracy, ball screws are often more precise. A rolling lead screw would have an accuracy of 75 microns across a 300 mm span, but a metric rolled ball screw may have an accuracy of 23 microns.
4.Repeatability
Ball screws are known to have higher repeatability because of their adjustable nut design, which tightens the spacing between the ball bearings, reducing “play” or backlash in the nut-to-screw movement.
Lead screws are available with anti-backlash designs, but unlike ball screws with circulating bearings, the sliding friction design of the lead screw can only have limited pressure to reduce its tolerances before stopping the lead screw from rotating.
5.Environmental
Lead screws are superior for applications that would benefit from a smoother, quieter operation. They don’t have the noise that comes with ball recirculation since they have fewer moving parts.
Lead screws are also advantageous in applications where corrosion resistance and cleanliness are crucial. Lead screws, which frequently don’t need to be lubricated, can lead to a more straightforward design that also has the advantage of being more resistant to contamination. For applications where the use of a ball screw can’t be avoided, mechanisms for minimizing the outflow of pollutants should be put in place.
6.ROI
Lead screws are often less expensive because of their ease of manufacturing due to their relative simplicity. However, it is impossible to evaluate system cost without taking into account the application environment.
Smooth and silent operation is frequently preferred by OEMs manufacturing lighter-load medical devices, such as insulin pumps and medical analyzers, over high precision, efficiency, or repeatability. Lead screws are therefore probably the most cost-effective option.
Ball screws will be necessary to achieve essential functionality for those creating high-precision systems for semiconductors, robotics, power steering, airplanes, and many industrial automation applications.
It’s also important to consider the end-user’s long-term cost of ownership. In terms of lifespan cost, ball screws are somewhat more cost-effective than lead screws. This is because there is less wear, heat, and friction.
However, the fact that lead screws don’t require lubrication offers end users a clear financial advantage, since they would normally need to account for maintenance expenses when calculating their return on investment.
Ball Screws and Lead Screws Comparison Chart
To see the differences, take a look at the below comparison chart:
| Ball Screws | Lead Screws | |
| Mechanism | Recirculating ball bearings | Threaded screw with plastic or metal nut |
| Industries and Applications | Large, industrial-scale applications | Smaller OEM applications |
| Price | Higher cost | Lower cost |
| Capacity | Higher load capacity | Lower load capacity |
| Design | Complex design | Simple design – easy to customise for applications |
| Operation | High efficiency, accuracy, precision. | Efficiency, accuracy, and precision are not as high. |
Conclusion
The biggest difference between a ball screw and lead screw is how they carry a load. Ball screws use ball bearings that recirculate to minimize friction and convert rotary motion to linear motion. Lead screws do not use ball bearings and rely on low coefficients of friction between the sliding surfaces. Lead screws, therefore, have higher friction making them less efficient than ball screws.
Lead screws are more suitable for simple transfer applications for which speed, accuracy, precision, and rigidity are not as critical.
Ball screws are more suitable in applications where higher loads and faster speeds are needed.
Ball Screw vs Lead Screw FAQs
1.Why is the difference between lead screws and ball screws so important?
First and foremost, everything boils down to mechanics. Even though both types of screws are mechanical linear actuators that may be employed in seemingly comparable settings, each project engineer must examine the back drive, backlash, thrust, speed, lead accuracy, and efficiency of the mechanism.
2.What are the benefits and uses of lead screws and ball screws?
Ball screws, while noisier, can handle bigger loads than lead screws, do not self-lock, are not as stiff, and typically provide much superior efficiency, precision, and accuracy. Ball screws are widely utilized in airplanes, power steering systems, robotics, and semiconductors.
Lead screws are frequently used in medical equipment, such as insulin pumps, and personal computing devices, such as desktop PCs, due to their quietness, smoothness, resistance to corrosion, self-lubrication, and often lower cost.
3.What are the top factors an engineer should consider when choosing between a lead screw and a ball screw?
The choice between a lead screw and a ball screw is relative and will most likely be determined by the application. For example, in a vertical application, a lead screw may be more advantageous than a ball screw since it cannot back drive itself. However, in a horizontal orientation, when no external force is applied to the application, using a ball screw is preferable since gravity does not pull it back.