How to Calculate Linear Guide Friction Force and Drive Motor Force

The running resistance of a linear guide can be estimated from the applied load and guide friction coefficient, but load friction is only part of the total resistance. Seals, preload, lubricant viscosity, installation error and external cable forces may also affect how much force the motor must produce.

For a preliminary calculation, the linear guide friction force can be expressed as:

This equation is useful for initial motor and actuator sizing. Final calculations should use the friction or running-resistance data published for the selected guide model, especially when the system uses heavy preload, reinforced seals or low-temperature grease.

What Creates Resistance in a Linear Guide?

A profile linear guide uses recirculating balls or rollers between the rail and carriage. Rolling contact produces much less resistance than a sliding guide, but the resistance is not zero.

The main sources are:

• Rolling friction: resistance generated between the rolling elements and raceways under load.
• Seal resistance: contact between the end-seal lips and guide rail.
• Preload resistance: internal loading used to remove clearance and increase rigidity.
• Lubricant resistance: grease viscosity, grease quantity and operating temperature affect running resistance.
• Installation resistance: rail misalignment, base deformation and uneven block mounting create internal forces.
• External resistance: cable carriers, bellows, hoses and process equipment may resist platform movement.

The calculated value therefore represents an estimate under correctly installed and lubricated conditions. A large difference between the calculation and measured force usually indicates that another source of resistance is present.

Step 1: Determine the Load Carried by the Guides

For a horizontal platform with a centered load, the total normal load carried by the guide system can initially be estimated from the moving mass:

Where:

• P = total normal load on the guide system (N)
• m = moving mass, including the table, workpiece and moving accessories (kg)
• g = gravitational acceleration, approximately 9.81 m/s²

For example, a 300 kg moving platform produces a total vertical load of:

Dividing this value equally among four blocks is acceptable only when the structure is rigid, symmetrical and the load acts near the center of the guide arrangement. An offset payload or process force creates roll, pitch or yaw moments, causing some blocks to carry more load than others.

When significant moments are present, calculate the load on the most heavily loaded block before checking guide capacity and service life. See our linear guide moment load calculation for a dual-rail, four-block arrangement.

Step 2: Select an Appropriate Friction Coefficient

A value around 0.002–0.003 is commonly used as a preliminary reference for many ball-type profile linear guides under suitable lubrication and normal operating conditions. Roller guides, miniature guides and guides with special internal structures may require different values.

The friction coefficient is not a universal constant. Using 0.003 for every guide, preload class, seal arrangement and operating temperature can produce an inaccurate result. Use a preliminary coefficient only before the exact guide configuration has been confirmed.

Step 3: Calculate Load-Dependent Rolling Friction

The basic load-dependent friction force is:

Using the previous 300 kg platform and an assumed coefficient of 0.003:

This result may appear surprisingly low. It represents only the load-dependent rolling resistance of a properly installed guide system. Seal drag, grease, preload and external accessories have not yet been included.

Step 4: Add Seal Resistance for Every Block

Seal resistance is normally specified per block. If four sealed blocks are installed, the resistance of all four blocks must be included:

If the assumed seal resistance is 3 N per block and the platform uses four blocks:

The estimated guide resistance becomes:

The 3 N value in this example is an assumption used to demonstrate the method. It is not a universal value or a DLY measured specification. The actual seal resistance must be confirmed for the selected guide series, block size, seal type and lubrication condition.

Why Seal Resistance Matters More in Light-Load Systems

Load-dependent friction decreases as the applied load becomes smaller, but seal resistance does not necessarily decrease in the same proportion. This is why simply calculating μP can significantly underestimate the force needed to move a lightly loaded positioning stage.

Consider two systems using four blocks with the same assumed seal resistance:

In the 30 kg example, estimating resistance from μP alone would omit most of the expected guide resistance.

Step 5: Calculate the Total Force Required to Move the Axis

The motor does not overcome only linear guide resistance. During acceleration, it must also accelerate the moving mass and overcome process forces and external resistance.

For a horizontal axis:

Assume the 300 kg platform operates under the following conditions:

• Acceleration: 2 m/s²
• Process force: 150 N
• Calculated guide resistance: 20.83 N
• Estimated cable carrier resistance: 25 N

The acceleration force is:

The total drive force during acceleration is:

For a direct-drive linear motor, this force contributes directly to the required thrust. Motor selection must still check continuous force, peak force, duty cycle, velocity and thermal limits.

Converting Drive Force into Ball Screw Torque

If the platform is driven by a ball screw, the linear force can be converted into screw torque:

Using a 10 mm lead ball screw and an assumed drive efficiency of 0.90:

This is the torque required to produce the calculated linear force. It is not yet the final motor torque. Ball screw rotational inertia, coupling inertia, bearing resistance, acceleration time, transmission ratio and safety allowance must also be checked.

For a complete drive calculation, refer to How to Calculate Ball Screw Motor Torque: Horizontal and Vertical Axis Examples.

Starting Resistance and Running Resistance Are Not Always Equal

Rolling linear guides normally have a relatively small difference between static and dynamic friction. However, the complete axis may still require more force when starting after a long stop.

Possible reasons include:

• grease redistribution or high grease viscosity;
• low ambient temperature;
• seal lips adhering slightly to the rail surface;
• preloaded blocks;
• cable carrier bending resistance;
• ball screw or support-bearing starting torque;
• misalignment that becomes more apparent during reversal.

A motor must be checked against both the highest starting or acceleration demand and the continuous running demand. Selecting it from steady-speed guide friction alone is not sufficient.

How to Measure Actual Linear Guide Running Resistance

When possible, measured resistance provides a better basis for final commissioning than a friction coefficient alone.

1. Disconnect the drive mechanism if this can be done safely, so ball screw and motor resistance do not affect the guide measurement.
2. Keep the normal moving platform and operating load installed.
3. Use a calibrated force gauge aligned with the direction of travel.
4. Pull the platform at a slow, stable speed rather than using a sudden force.
5. Measure in both directions and at several positions along the stroke.
6. Record the peak starting force and stable moving force separately.

A force that remains consistently higher in one direction may indicate an external cable or seal effect. A local force peak at one position more often suggests contamination, rail deformation, mounting-surface error or poor parallelism.

What If the Measured Resistance Is Too High?

If the platform becomes tight after the second rail or moving table is fully tightened, increasing motor torque is not the correct first response. Installation-induced internal stress can increase heat and shorten guide life even when the motor is powerful enough to move the axis.

See How to Install Linear Motion Guides for mounting-surface preparation, reference-rail alignment and tightening procedures.

Information Needed for a Reliable Calculation

Before selecting a linear guide or drive motor, confirm the following:

• moving mass and payload;
• guide series, size and block quantity;
• ball-type or roller-type guide;
• preload or clearance class;
• seal and scraper configuration;
• rail orientation and load direction;
• maximum speed and acceleration;
• working or process force;
• ball screw lead or direct-drive arrangement;
• cable carrier, bellows and hose resistance;
• operating temperature and lubrication condition.

For DLY linear guide selection, the model and block arrangement should be confirmed together with the actual load, mounting layout and working environment. Running resistance should not be judged only from the dynamic load rating, because load capacity and friction resistance describe different aspects of guide performance.

Conclusion

For an initial estimate, linear guide resistance can be calculated from the load-dependent rolling friction plus seal and additional resistance:

The guide resistance is then added to acceleration force, process force and external accessory resistance to determine the total axis drive force. For ball screw systems, this force can be converted into load torque, but screw inertia, support bearings, coupling inertia and motor operating conditions must still be evaluated separately.

The most important practical point is that excessive resistance should not automatically be solved by choosing a larger motor. If measured resistance changes sharply along the stroke or increases after assembly, first inspect rail alignment, mounting surfaces, lubrication, seals and platform deformation.

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