In machine building, there is a strong temptation to select components based on experience or a “gut feeling.” An engineer wants to move fast, while a purchaser looks for the sharpest price. Yet a solid theoretical foundation is the cornerstone of every reliable machine. Technical calculations within the manufacturing and machine-building industries are not merely a formality, but an essential validation of the design.
Service life calculation: more than just a number on paper
A service life calculation provides the essential framework for the uptime of your installation. We express this result in kilometers, operating hours, or total number of cycles. In doing so, we look beyond static load alone; it is the dynamic interaction of forces that truly matters.
To arrive at a reliable recommendation, we analyze the following variables:
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Speed and acceleration: The faster a mass is set in motion, the greater the impact on the balls and raceways.
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Duty cycle and cycle time: Heat generation and lubrication intervals are directly linked to these parameters.
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Center of gravity of the mass: An incorrectly estimated center of gravity results in unexpected moment loads on the carriages.
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Installation orientation: Whether a guide is mounted horizontally, vertically, or on a wall determines how gravity influences the load.
Our approach is deliberately conservative. While some competitors calculate with a probability of 50%, LM Systems ensures that in 90% of cases the theoretically calculated service life is actually achievable. This provides the confidence you need to defend your design internally.
Stiffness and static safety
In addition to service life, precision under load is crucial for the quality of the end product. We perform stiffness calculations using specific stiffness diagrams. By accurately plotting the external load against this data, we calculate the degree of deflection or deformation. This is essential for applications such as machining or high-tech assembly, where micrometer-level precision is required.
Static safety logically follows from the type of guide and the selected size, provided that the input data for the service life calculation is complete. This prevents incidental shock loads from causing plastic deformation of the ball tracks (brinelling), which would immediately compromise running accuracy.
Critical parameters for screws: speed and buckling load
When using ball screws, a standard calculation is not sufficient. Two specific risk factors play a major role here and are often underestimated:
1. Critical speed
For a screw, we always verify whether the required rotational speed is compatible with the diameter and free length. If the so-called DN value is exceeded, vibrations and resonances occur that can destroy the screw in a short time. We calculate a safe margin to ensure stable operation, even at high speeds.
2. Buckling load
Buckling load is an integral part of calculating the service life of a screw. A screw subjected to tensile load can generally withstand more than one subjected to compressive load. We validate that the screw will not fail (buckle) under the maximum axial force.
Deriving the drive torque
Once all data required for the service life calculation (such as friction, mass, acceleration, and lead) is known, we can usually derive an accurate drive torque. This is valuable information for the engineer, as it enables the correct motor and transmission to be selected without over-dimensioning.
Why choosing “by feel” is a risk
When an engineer selects a component without calculations, the project is exposed to unnecessary risk. The greatest danger is failing to achieve the required service life. This results in premature failure with serious consequences: from irritating machine downtime to the shutdown of an entire production line or even a complete factory. The cost of such downtime never outweighs the time required to perform a proper calculation.
Honest advice: smaller is sometimes better, larger is often smarter
Our drive to help means we sell what is needed, not what is most expensive. It is quite common for a calculation to show that a customer can use a smaller or more economical product, saving weight, space, and cost.
However, the opposite also applies. Sometimes, during the engineering process, we uncover forces that were not initially considered. A good example is the choice between size 15 and size 25. An engineer may want to design compactly (size 15), but this requires mounting with M4 bolts. In such cases, we often recommend size 25, which uses M6 bolts. This significantly increases stiffness and service life, allowing the machine to exceed its expected lifespan (provided that consistent maintenance is performed).
What can you expect from LM Systems?
At LM Systems, a technical calculation is not an additional cost item on the quotation. We consider it a complimentary service and an integral part of our craftsmanship. In most cases, we already exchange these calculations with your engineering team during the preliminary phase. As a result, the outcome is often known before the formal quotation is issued.
We apply strict safety factors:
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Individual components: minimum safety factor of 5
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Assemblies (such as modules): minimum safety factor of 10
These generous margins eliminate design risk and ensure a robust end product you can be proud of as a machine builder. LM Systems thinks along with you as an engineering partner and translates your requirements into a reliable solution. Contact us and discover what customization means for your application.