How to Select the Ideal Linear Shaft for Your Application
Shaft bars are used in many linear, rotary and static applications. In this guide we only consider the product being used in a linear motion system.
Motion control systems regulate and manage the movement of machinery and equipment, including controlling speed, position, and torque. Linear shafts are key components in these systems. They’re used in applications ranging from 3D printers to automotive systems. But what exactly are linear shafts and what do they do? This guide explains what you should know, covering:
What are linear shafts and how do they work?
Linear shafts are straight, precision-machined bars in mechanical systems that require linear motion or load support. They serve as guides and enable the precise and smooth movement of loads along a straight path, contributing to the efficiency and performance of various industrial and automation applications.
They typically take the form of cylindrical rods and are commonly paired with linear Ball Bushes, bushings, or similar linear motion components to create a seamless and precise linear motion system. It's important to note that linear shafts and Ball Bushes do not transmit rotational motion. The best application for these products is direct load as the ball bushes don’t tend to accept moment loads.
Linear shafts often serve as structural components to bear and transfer loads in a linear motion system. To enable linear motion, linear shafts are integrated with linear ball bushes or ceramic bushings. These linear ball bushes or ceramic bearings are affixed to the shaft, allowing it to move smoothly along its axis with minimal friction. If linear ball bushes are used the system can only be used in a linear motion. If you require some rotary motion, consider ceramic bushes.
Linear shafts allow for highly accurate positioning. Their operation is notably quiet, generating minimal vibrations, which translates to reduced energy consumption and decreased wear and tear on associated components. Typically, linear shafts receive support from two or more shaft holders or linear bearings within the machine framework and may experience torsional stress.
Linear shafts are engineered to withstand various types of loads, including axial (along the shaft's length) and radial (perpendicular to the shaft's length) loads. The load-bearing capacity depends on factors such as the material, diameter, length, surface finish of the shaft, and the support provided by the linear bearings or bushings.
The quality of linear shafts and their associated linear bushings significantly impacts the precision and smoothness of the linear motion system. High-quality components reduce friction and minimise play or backlash, ensuring precise and consistent movement.
What is Tolerance Class?
Tolerance class or tolerance grade specifies the allowable dimensional variations or tolerances for the shaft's diameter. It indicates how precisely the shaft's diameter must adhere to its nominal or ideal dimension.
Tight Tolerance Class
In this case, the shaft is manufactured to very precise and tight dimensional tolerances. The "h6" tolerance class, for instance, indicates that the shaft's actual diameter can vary within a very narrow range around the nominal diameter. This results in a high level of precision and ensures that the shaft has minimal deviation from the specified size. Linear shafts with tight tolerance classes are suitable for applications where precise fits and accurate linear motion are crucial, such as in machinery and robotics.
Loose Tolerance Class
Conversely, a loose tolerance class, such as "h9," allows for more significant variations in the shaft's diameter compared to the nominal size. Shafts with loose tolerance classes are manufactured with a wider allowable range of dimensions. These shafts are typically more cost-effective but may not provide the same level of precision as those with tighter tolerances. They are suitable for applications where high precision is not critical, and a lower level of accuracy is acceptable.
Typical linear shaft applications
The choice of material plays a critical role in linear-shaft selection. Keep in mind that shaft material considerations determine the component’s ability to withstand various forces and maintain precise linear motion over time.
All of our linear shafts belong to the h6 tolerance class.
- Robust, high-quality carbon steel
- Material has undergone a specialised hardening process, resulting in increased strength, longevity, and resistance to wear and corrosion
- Used with all types of linear ball bushings for smooth and precise linear motion
- Combine exceptional size precision, straightness, and concentricity to reduce wear in high-speed applications
- Exceptional performance
Typical applications: Industrial machinery, automotive systems, and medical devices
Hardened Hollow Shafts - Carbon Steel
- Robust, reliable, high strength and durable
- Used with linear bushings when weight reduction is necessary, but structural integrity is not compromised
- Weight reduction enables greater efficiency, lower energy usage, and increased manoeuvrability
- Design allows fluids, gases, or electrical wires to travel through its centre
- When paired with a linear ball bushing, it offers smooth and accurate linear motion
Typical applications: Industrial machinery, automotive systems, and medical devices
Hardened Stainless Shafts - Corrosion Resistant Steel
- Great strength, durability, and reliability.
- Used with linear ball bushes for smooth and precise linear motion
- Suited for demanding applications requiring corrosion and wear resistance
- Stands up to harsh conditions such as humidity or chemicals without sacrificing structural integrity
- Little maintenance needed, reducing downtime and operating expenses
Typical applications: Food processing equipment, automotive systems, and medical devices
- Excellent for industries that demand exceptional corrosion resistance, strength, and durability
- Tolerates difficult conditions such as high humidity and chemicals
- High-temperature resistance and excellent weldability
- Long lifespan with less downtime and lower operational expenses
- Suitable for applications involving heavy loads, high speeds, and abrasive environments
Note: These are not meant for use with a linear ball bearing. Use with self-lubricating ceramic bushings.
Typical applications: Equipment for X-rays, paper processing, hardware, and food processing
- Versatile, non-magnetic, and lightweight
- Sturdy and durable
- Great strength-to-weight ratio
- Provides thermal conductivity
- Good corrosion resistance offers a longer lifespan for shafts and avoids the need for regular maintenance or replacement
- Operating temperature range: -130°C to +200°C
Note: These are not meant for use with ball bush linear bearings. Use with self-lubricating ceramic bushings.
Typical applications: Oil and gas equipment and medical devices. Also used in the construction sector and the automobile industry
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How to choose the right linear shaft
To ensure optimal functionality and durability, you have to make sure your linear-shaft selection is appropriate. Follow these steps to make an informed decision:
1. Define Your Application Requirements
Outline your application's specific needs, including factors such as load capacity, speed, precision prerequisites, environmental conditions, and the intended role of the linear shaft within your system.
2. Shaft Material Considerations
Thoroughly assess the material choice for the linear shaft in line with your application's unique demands. Prioritise the most important factors, such as corrosion resistance, which stainless steel shafts offer.
3. Choose the correct Shaft Diameter
The required shaft diameter should be based on load magnitude, operational speed, and other application-specific variables. Ensure that the chosen diameter can adequately support the anticipated loads without undue deflection or wear.
4. Consider Shaft Hardness
Depending on the application's nature, you might need a shaft with specific hardness characteristics. Hardened shafts are known for their enhanced wear resistance, rendering them suitable for high-wear scenarios.
5. Evaluate Tolerance Class
Take into account the tolerance class associated with the shaft. Remember, a tighter tolerance class signifies heightened precision but may entail a higher cost. Opt for the tolerance class that aligns with your application's precision prerequisites.
6. The Right Shaft Length
Ascertain the appropriate shaft length, factoring in considerations such as travel distance and mounting requirements. The shaft's length should adequately accommodate the full stroke length as needed.
7. End Support Planning
Think about the support for the shaft at its ends. Depending on your application, you may need support elements such as blocks or bearings to ensure stability and minimise deflection.
8. Load Type Considerations
You’ll need to consider the different load types that linear shafts are engineered to handle, encompassing radial, axial, or a combination thereof. Choose a shaft that corresponds to the specific load type for your application.
9. Budget and Cost Analysis
Factor in your budget constraints and conduct a comprehensive cost assessment of the chosen linear shaft. Strike a balanced decision that reconciles your requirements with the available budget, ensuring cost-effectiveness.
10. Testing and Validation
Finally, consider subjecting the selected linear shaft to testing and validation in the context of your specific application before full-scale integration. This rigorous evaluation guarantees alignment with your performance expectations.
Surface compatibility and resistance of linear shafts
These are crucial factors to consider when choosing linear shafts for specific applications. They significantly impact the performance and durability of the shaft in its intended environment. Let's delve deeper into these aspects:
Surface Compatibility
Surface compatibility of linear shafts relates to the alignment of the material and finish with the requirements of the application. It involves assessing whether the shaft's surface attributes, including material composition and surface treatment, are a suitable match for the intended use. Key considerations encompass:
- Shaft Material Considerations: Opt for a material that stands up to the operational environment. For example, stainless steel proves effective in harsh environments prone to corrosion due to its inherent resistance, while carbon steel offers enhanced wear resistance.
- Coatings and Treatments: Certain linear shafts feature specialised coatings or treatments to augment their surface characteristics. These can range from coatings that bolster corrosion resistance to surface hardening treatments that elevate wear resistance.
- Surface Finish: The surface finish of the shaft plays a pivotal role in influencing factors like friction and wear. It's imperative to ensure that the surface finish aligns with the type of linear motion employed and any sealing elements used within the application.
- Compatibility of linear shafts with Bearings and Bushings: Compatibility between the shaft's surface and these components is essential to minimise friction and mitigate wear.
Resistance to Environmental Factors
Resistance of linear shafts to environmental factors is a paramount consideration to guarantee the components’ long-term reliability. The specific environment in which the shaft operates may pose certain challenges, including:
- Corrosion Resistance: Linear shafts exposed to moisture, chemicals, or outdoor conditions should possess robust corrosion resistance. Stainless steel and select coatings can furnish effective safeguards against corrosion.
- Abrasion and Wear Resistance: Applications characterised by high friction or abrasive conditions necessitate linear shafts equipped with surfaces or coatings engineered to withstand wear and extend service life.
- Temperature Endurance: Resistance of linear shafts to the prevailing temperatures in the application is crucial. Otherwise, you’re compromising its material properties or looking at the shafts succumbing to permanent deformation.
- Chemical Compatibility: In scenarios involving exposure to chemicals, the choice of shaft material should withstand the specific chemicals that might come into contact with it.
- Cleanliness and Contamination Control: Environments mandating cleanliness and stringent contamination control, such as in the semiconductor industry, demand linear shafts characterised by smooth, easy-to-clean surfaces to avert the generation of particles.
Maintenance and longevity of linear shafts
Regular maintenance directly affects the longevity of linear shafts by ensuring optimal performance. Here’s an overview of maintenance strategies and the factors that influence the durability of linear shafts:
Maintenance Strategies:
- Routine Inspection: Establish a regular inspection schedule to evaluate the condition of linear shafts. Look for indications of wear, corrosion, misalignment, or damage. Detecting problems early allows for timely corrective actions.
- Lubrication: Adequate lubrication is critical for minimising friction and wear between the shaft and associated components such as bushings. Adhere to the manufacturer's recommendations regarding lubrication intervals and the appropriate lubricants to use.
- Cleanliness: Maintain a clean operating environment to prevent the accumulation of debris, dust, and contaminants on the shaft's surface. Contaminants can accelerate wear and lead to premature failure.
- Shaft Alignment: Ensure proper shaft alignment with other system components, such as linear guides and bearings. Misalignment can result in uneven wear and a reduced lifespan.
- Load Distribution: Distribute loads evenly across the linear shaft to prevent localised wear and stress concentrations. Proper load distribution contributes to a longer shaft life.
- Protection: Implement protective measures like shaft covers, bellows, or seals to shield the shaft from environmental factors such as moisture, dust, and abrasive particles. By doing this, you improve the longevity of linear shifts in your applications.
- Replacement of Worn Components: When inspections reveal significant wear or damage, promptly replace worn components. Delaying replacement can lead to further damage and decreased system performance.
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If you need help with your linear shaft selection, our experts are always happy to advise you.
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Questions?
Email us at sales@essentracomponents.co.uk or speak to one of our experts for further information on the ideal solution for your application 0345 528 0474.