Selecting Linear Guides, Calculating Service Life
5 units · approx. 36 minutes total · Step 1 of 8
Getting Started
This module focuses on the selection and design of linear guides—from design type and static safety to L10 service life calculations. You will learn how static and dynamic load ratings, safety factors, and service life are mathematically related, and how ball, roller, and slide guides differ fundamentally.
The course concludes by examining how the installation orientation, preload, and torque load affect the actual service life. Calculation exercises, a decision tree, flashcards, and a case study bring the theory to life; a self-test at the end tests your understanding of the material.
Learning Objectives – After completing this module, you will be able to:
- Distinguish between different types of linear guides (profiled rail, cage, round shaft; ball, roller, sliding);
- calculate the static load rating C₀ and the safety factor S₀ = C₀/P₀, and apply guideline values;
- Calculate the L10 service life formula for ball and roller guides and convert it to operating hours;
- Select ball and roller guides based on stiffness, load rating, accuracy, and cost;
- Take into account the installation orientation, preload, accuracy classes, and torque load during installation.
Learning units
Five short learning units (7–8 minutes) with learning objectives, examples, and knowledge checks—standalone learning content for this module, maintained independently of the website’s guides. Progress is saved locally in this browser.
0 of 5 units
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- Unit 1 of 5
Linear Guides: An Overview
approx. 7 minutes
Open - Unit 2 of 5
Load Ratings and Static Safety
approx. 7 minutes
Open - Unit 3 of 5
Calculating Service Life
approx. 8 minutes
Open - Unit 4 of 5
Ball or Roller Guides
approx. 7 minutes
Open - Unit 5 of 5
Installation, Accuracy, and Stiffness
approx. 7 minutes
Open
Calculation Exercise 1: Static Safety
A carriage has a static load rating of C₀ = 50 kN. The maximum load that occurs is F = 10 kN.
Calculate the static safety factor S₀.
Calculation Exercise 2: L10 service life
A roller guide (line contact, exponent 10/3) has a dynamic load rating of C = 25 kN at an equivalent operating load of P = 5 kN.
Calculate L10 in units of 10⁵ m.
For verification: Service life calculator (opens in a new tab)
Decision Tree: Ball or Roller?
Four quick questions about load, speed, stiffness, and accuracy—you’ll receive a well-reasoned recommendation with a link to the appropriate guide.
This feature needs JavaScript. You can reach the same recommendation using this overview.
Questions and answers
- What is the load on the guide? (The decisive factor is the maximum load that occurs, including brief peak loads.)
- High to intermittent – Heavy-duty applications, presses, large gantry systems, molding machine tables
- Moderate – Typical load of a machine tool or handling axis
- How fast does the axis need to move? (Ball guides are designed for dynamic performance, while roller guides are designed for high load capacity.)
- Fast (up to 5 m/s) – Assembly, pick-and-place, dynamic axes
- Slower (2–3 m/s or less) – Heavy-duty positioners, presses, molding machines
- How important is maximum stiffness against breakdown torque? (Relevant for cantilevered loads or high machining forces.)
- Very important – Cantilevered load, milling or cutting forces
- Secondary – Breakdown torques are small or well distributed
- How important is positioning accuracy in the micrometer range? (Relevant for precision axes and measurement technology.)
- Very important – Precision class, measurement or optical technology
- Secondary – Standard positioning accuracy is sufficient
Recommendations
The first matching line applies.
- If What is the load on the guide?: High to intermittent → Recommendation: Recommendation: Roller guide – For high or shock loads, roller guides are the preferred choice: The linear contact provides higher load-carrying capacity (especially static) and stiffness than a ball guide for the same size—the exact factor depends on the manufacturer. Typical applications: presses, heavy-duty positioners, large gantries.
- If How fast does the axis need to move?: Fast (up to 5 m/s) → Recommendation: Recommendation: Ball guide – For high-speed axes up to 5 m/s, ball guides are the right choice: The point contact generates low friction and allows for high travel speeds—roller guides are usually limited to 2–3 m/s in continuous operation.
- If How important is maximum stiffness against breakdown torque?: Very important → Recommendation: Recommendation: Roller guide – If maximum stiffness against breakdown torque is critical, the linear contact profile makes the roller guide the better choice: it has less elastic deflection than a ball guide, but slightly higher friction.
- If How important is positioning accuracy in the micrometer range?: Very important → Recommendation: Recommendation: Ball guide – When it comes to positioning accuracy in the micrometer range, ball guides are the clear leader: repeatability of ±0.01 to 0.05 mm can be achieved, and with preload, they can even be made backlash-free—roller guides typically achieve only ±0.05 to 0.1 mm.
- In all other cases → Recommendation: Recommendation: Ball guide – Unless there are specific requirements regarding load, speed, stiffness, or accuracy, ball guides are the more cost-effective standard solution—a wide range of models is available at a lower purchase price than specialized roller guides.
Flashcards: Linear Guide Terminology
Eight technical terms from the glossary—click on the card (or press Enter or the spacebar) to see the definition.
Flashcards
Tap to see the definition.
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- Linear Guides
- Linear motion guidance systems—available as profile rail, cage, or round-shaft guides with balls, rollers, or sliding elements as rolling or sliding bodies. Source: Glossary “Linear Guides”
- Static load rating (C₀)
- Static load at which the permanent deformation of the rolling elements and raceway is just within tolerable limits (ISO 14728-2). Basis for the safety factor S₀ = C₀/P₀. Source: Glossary “Static load rating (C₀)”
- Dynamic load rating (C)
- The load at which a guide series reaches its nominal L10 service life (ISO 14728-1). Thanks to line contact, roller guides achieve higher C-values than ball guides of the same size. Source: Glossary “Dynamic load rating (C)”
- L10 service life
- Running distance (in 10⁵ m) that at least 90% of a guide series can achieve without fatigue damage. L10 = (C/P)^p, where p = 3 (ball) or 10/3 (roller). Source: Glossary “L10 service life”
- Crossed-roller guide
- Guide with rollers alternately crossed at 90°—accommodates loads from all directions, can be preloaded to be very rigid and backlash-free, but has a limited stroke (cage length). Source: Glossary “Crossed-roller guide”
- Roller recirculation
- Rolling elements circulate in a closed loop within the carriage—enabling a theoretically unlimited stroke, in contrast to cage-guided (non-circulating) guides. Source: Glossary “Roller recirculation”
- Cage positive guidance
- Mechanical synchronization of the rolling element cage—usually via a rack and pinion—prevents cage drift during vibration, dynamic operation, or changes in direction. Source: Glossary “Cage positive guidance”
- Stiffness (Linear Guide)
- Ratio of load to elastic deformation (N/µm). Thanks to line contact, roller guides achieve values approximately 2 to 3 times higher than comparable ball guides. Source: Glossary “Stiffness (Linear Guide)”
All cards in this unit have been shown. The unknown ones are now in the review stack.
Case Study: Measuring Machine – Stiffness vs. Cost
A customer in the measuring machine industry is planning a coordinate measuring machine with a short travel distance (stroke approx. 300 mm) that requires the highest positioning accuracy and maximum stiffness against breakdown torque because the probe extends laterally. The designer is torn between a standard ball-screw guide—which is already installed in many other machines at the company and can be procured at a low cost—and a specialized cage/crossed-roller guide, which is more expensive but, according to the data sheet, is significantly stiffer and can be preloaded to eliminate play. The budget for the axis is limited.
Key Questions
- Which design offers the highest stiffness and precision for short strokes—and why?
- What trade-offs does this design entail compared to a standard profile rail guide?
- Under what conditions would the standard ball-profiled rail be an acceptable choice despite its lower stiffness?
View Worked Solution
1. The cage/crossed-roller guide: Rollers crossed at 90° in an alternating pattern absorb loads from all directions; contact is linear (greater stiffness than point contact), and the guide can be preloaded to eliminate play—resulting in exceptionally smooth operation and straightness within a compact installation space.
2. The stroke is limited to approximately twice the cage length—which is not critical for the 300 mm in this application, but would preclude a longer travel distance. In addition, when the system remains stationary in one position for a long time, “cage creep” must be taken into account in the design, for example, by using cage positive guidance.
3. If a significantly longer stroke were required, or if the tilting moment load could be controlled through a more symmetrical design (e.g., two carriages spaced farther apart), the more economical standard profile rail might be sufficient—the additional stiffness of the crossed-roller guide is only worthwhile if accuracy and tilting moment capacity are indeed the critical requirements.
Technical Background: Selecting a Linear Guide (opens in a new tab) and Ball vs. Roller Guides (opens in a new tab)
Self-test
10 questions about this module—immediate feedback with explanations and source links. The module is considered complete if you score 7 out of 10 points or higher.
Self-test
10 questions for this module. You see right after each answer whether it was correct.
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Before each answer, you state how confident you feel. This helps distinguish knowledge gaps from uncertainty. It has no effect on the score.
Question 1 of 10
Advanced Topics (optional)
The three linear guide guides on the website, in case you’d like to delve deeper. Reading them is not required for the learning units and self-test in this module.