How to Calculate Linear Guide Life

Oct 8

Linear guide life is calculated from the guide’s basic dynamic load rating, the fatigue-equivalent load carried by the most highly stressed carriage over the operating cycle, and the manufacturer’s life equation for that guide type. For ball-type guides, the load-life relationship commonly uses an exponent of 3; for roller-type guides, it commonly uses an exponent of 10/3.

For THK profile rail guides using its stated rating conventions:

Ball guide:

L₁₀ = (C / Pᶜ)³ × 50 km

Roller guide:

L₁₀ = (C / Pᶜ)^(10/3) × 100 km

where:

L₁₀ = nominal life,
C = basic dynamic load rating,
Pᶜ = calculated equivalent load acting on the carriage.

THK defines nominal life as the travel distance that 90% of a group of identical guides operating under the same conditions can achieve without rolling-fatigue flaking.

The critical qualification is that you cannot calculate meaningful guide life until you have first calculated the actual load on each carriage.

The correct sequence is:

machine loads → individual carriage loads → equivalent/average load → dynamic rating C → nominal life → operating hours

Key Takeaways

Linear guide fatigue life is primarily calculated from C/P, not from payload weight alone.
C is the basic dynamic load rating.
P is the calculated fatigue-equivalent load on the carriage.
Ball guides and roller guides use different load-life exponents.
THK’s applicable ball-guide ratings are commonly referenced to 50 km.
THK’s applicable roller-guide ratings are commonly referenced to 100 km.
Rating bases must be normalized before comparing guides from different catalogs.
Peak load is not necessarily the correct load for fatigue-life calculation.
Variable machine-cycle loads require an equivalent average load.
Because life varies approximately with the cube of load for ball guides, relatively small reductions in carriage load can create very large increases in calculated life.
Preload can add internal rolling-element load and may need to be considered.
Shock, vibration, contamination, lubrication, temperature, mounting accuracy, and raceway hardness can make real service life differ substantially from ideal nominal life.
Short-stroke applications require special attention.
The guide system’s life is effectively controlled by its most critically loaded carriage.

What Does “Linear Guide Life” Mean?

Linear guide life usually refers to rolling-fatigue life.

As the carriage travels, the:

balls or rollers,
carriage raceways,
rail raceways

experience repeated contact stress.

Eventually, rolling fatigue can produce surface flaking.

THK defines LM Guide service life as the total travel distance until the first fatigue flaking occurs on the raceway or rolling elements. THK — Nominal Life

This is different from a guide becoming unusable because of:

contamination,
corrosion,
lubrication failure,
collision,
damaged seals,
installation error.

Those failures can occur long before theoretical fatigue life is reached.

What Is L₁₀ Life?

L₁₀ is the nominal rating life associated with 90% reliability under the defined rating conditions.

That means if a sufficiently large group of nominally identical guides operates under identical conditions:

90% are expected to reach or exceed L₁₀ without rolling-fatigue flaking.

It does not mean every guide fails exactly at the calculated distance.

Schaeffler likewise defines its basic rating life on the basis that 90% of a sufficiently large population reaches or exceeds the calculated life. Schaeffler — Precision Rail Guides

What Is the Basic Dynamic Load Rating C?

The basic dynamic load rating C is the catalog value used in fatigue-life calculation.

It is not:

maximum allowable load,
static load rating,
payload capacity.

The static rating is:

C₀

The dynamic rating is:

A guide can have plenty of static capacity but still have inadequate fatigue life if its operating load is high relative to C.

The Core Ball-Guide Life Formula

For a THK ball-type LM Guide whose basic dynamic load rating is based on a 50 km reference distance:

L₁₀ = (C / Pᶜ)³ × 50

where:

L₁₀ = nominal life in km,
C = basic dynamic load rating,
Pᶜ = calculated load.

THK publishes this relationship for its applicable ball-type LM Guides. THK — Nominal Life

Ball-Guide Worked Example

Suppose:

C = 27.6 kN

and:

Pᶜ = 5.0 kN

Then:

C / P = 27.6 / 5

C / P = 5.52

Life:

L₁₀ = 5.52³ × 50

5.52³ ≈ 168.2

Therefore:

L₁₀ ≈ 8,410 km

That is the nominal fatigue-life travel distance under the assumed constant equivalent load.

Why Load Has Such a Huge Effect on Ball-Guide Life

Because load is raised to the third power.

Suppose the guide remains the same:

C = 27.6 kN

At 5 kN Load

L₁₀ ≈ 8,410 km

At 4 kN Load

L₁₀ = (27.6 / 4)³ × 50

L₁₀ ≈ 16,400 km

Reducing load by only:

20%

nearly doubles calculated nominal life.

That is one of the most important lessons in linear-guide design:

Improving machine geometry can produce enormous life gains.

The Roller-Guide Life Formula

For THK roller-type LM Guides using a basic dynamic load rating referenced to 100 km:

L₁₀ = (C / Pᶜ)^(10/3) × 100

THK identifies the 100 km reference distance for its applicable roller-type guide ratings and warns designers to account for the reference basis when comparing dynamic load ratings. THK — Nominal Life

Schaeffler also publishes the roller-bearing relationship using the 10/3 exponent and 100 km basis in its linear-guide engineering documentation.

Roller-Guide Worked Example

Suppose:

C = 40 kN

and:

P = 10 kN

Then:

C / P = 4

Life:

L₁₀ = 4^(10/3) × 100

4^(10/3) ≈ 101.6

Therefore:

L₁₀ ≈ 10,160 km

Again, this is nominal fatigue life under the assumed calculation conditions.

Ball and Roller C Ratings Cannot Always Be Compared Directly

This deserves special attention.

A manufacturer may publish ball-guide C on a:

50 km rating basis

and roller-guide C on a:

100 km rating basis.

If you compare the catalog values directly without recognizing the basis, you can reach the wrong conclusion.

THK explicitly says that C values should be converted according to ISO 14728-1 where necessary when comparing ratings based on different reference distances.

Example of C₅₀ vs. C₁₀₀

For applicable ball-bearing ratings, THK publishes the conversion:

C₁₀₀ = C₅₀ / 1.26

So if:

C₅₀ = 25.2 kN

then:

C₁₀₀ ≈ 20.0 kN

The physical bearing did not suddenly become weaker.

The number changed because the rating was expressed against a different reference life distance. THK technical reference

Step 1: Calculate Load on Every Carriage First

Before calculating life, determine the actual load on:

Block 1,
Block 2,
Block 3,
Block 4,

or however many blocks the machine uses.

Do not assume:

total payload ÷ number of blocks.

The loads may differ because of:

center-of-gravity offset,
pitch moment,
yaw moment,
roll moment,
acceleration,
deceleration,
process forces.

THK’s formal selection process calculates the applied load on each carriage before moving to equivalent load, average load, and nominal life. THK — Selection Criteria

Step 2: Convert Directional Loads to Equivalent Load

A carriage may simultaneously experience:

radial load,
reverse-radial load,
lateral load.

The manufacturer may require these to be converted into an equivalent load.

Do this before the fatigue-life calculation.

The exact equation and directional factors depend on the guide family.

Do not invent a universal equivalent-load formula.

Step 3: Calculate Load for Every Machine Phase

A real machine cycle may include:

stationary loading,
acceleration,
constant-speed travel,
process operation,
deceleration,
return travel.

The load on a carriage may be different in every phase.

For example:

Operating PhaseCarriage LoadAcceleration5,000 NConstant speed2,000 NProcess4,000 NDeceleration6,000 NReturn1,500 N

You should not simply use:

6,000 N

for the entire fatigue-life calculation unless that load genuinely acts over the whole travel.

Nor should you use a simple arithmetic average.

Why Arithmetic Average Load Is Wrong

Rolling fatigue is nonlinear.

For a ball guide:

life ∝ 1 / P³

Therefore, a brief high-load condition contributes disproportionately to fatigue damage.

THK defines average load as the constant load that would give the same service life as the actual fluctuating loads. THK — Average Load

That is a fatigue-equivalent average, not an ordinary arithmetic average.

Stepwise Average Load for Ball Guides

For a ball guide under several constant load levels acting over different travel distances, the fatigue-equivalent average load can be expressed conceptually as:

Pm = [(P₁³L₁ + P₂³L₂ + ... + Pₙ³Lₙ) / L]^(1/3)

where:

Pm = equivalent average load,
P₁…Pₙ = loads during each phase,
L₁…Lₙ = travel distance at each load,
L = total travel distance.

This follows the ball-bearing cubic fatigue relationship used in manufacturer average-load methodology.

Example of Why Average Load Matters

Suppose a ball guide experiences:

2,000 N for 75% of travel,
6,000 N for 25% of travel.

Arithmetic average:

(2,000 × 0.75) + (6,000 × 0.25)

= 3,000 N

But fatigue-equivalent load:

Pm = [(2,000³ × 0.75) + (6,000³ × 0.25)]^(1/3)

This gives approximately:

3,900 N

That is substantially higher than the simple 3,000 N average.

Using arithmetic average would overestimate life.

Roller Guides Use a Different Average-Load Exponent

Because roller fatigue uses a:

10/3 exponent

the equivalent-load calculation must use the applicable roller relationship.

This is another reason to identify:

ball guide,
roller guide

before performing a life calculation.

Step 4: Identify the Life-Limiting Carriage

Suppose a four-block system produces equivalent average loads of:

Block 1: 3.1 kN
Block 2: 4.8 kN
Block 3: 2.9 kN
Block 4: 3.4 kN

Block 2 will normally have the shortest calculated fatigue life if the blocks are otherwise identical.

The system's calculated guide life is therefore controlled by:

Block 2.

THK’s own life examples calculate life for each LM block and then identify the shortest block life as the relevant system life.

Step 5: Use C—not C₀—in the Life Equation

This mistake is common.

Use:

C = basic dynamic load rating

for fatigue life.

Use:

C₀ = basic static load rating

for static-safety evaluation.

Do not substitute C₀ into the L₁₀ formula.

Static Safety and Fatigue Life Are Separate Checks

A complete guide selection should pass both.

Static Check

Ask:

Can the guide safely withstand its worst peak load?

Typical relationship:

fs = C₀ / Pmax

Life Check

Ask:

Can the guide survive repeated rolling-contact cycles for the required travel distance or operating hours?

This uses:

C/P

and the appropriate fatigue exponent.

A guide can pass one and fail the other.

Step 6: Convert Travel Life to Operating Hours

A calculated life in kilometers is often difficult for a plant or machine builder to interpret.

Convert it to:

hours,
years,
machine cycles.

If:

stroke = S,
reciprocations per minute = n,

each complete reciprocation travels:

Therefore, travel per minute is:

2 × S × n

If S is in meters:

Travel per hour = 2 × S × n × 60

Then:

Life hours = total life distance / travel per hour

Life-in-Hours Example

Suppose:

L₁₀ = 8,410 km

Stroke:

1.0 m

Reciprocations:

10 per minute

Distance per full reciprocation:

2 m

Travel per minute:

2 × 10 = 20 m/min

Travel per hour:

20 × 60 = 1,200 m/h

= 1.2 km/h

Life:

8,410 / 1.2

≈ 7,008 hours

If the machine operates:

16 hours/day

then:

7,008 / 16 ≈ 438 operating days

Again, that is nominal fatigue-life calculation, not a guarantee of maintenance-free operation.

Step 7: Convert Hours to Years Carefully

Suppose calculated life is:

20,000 operating hours.

If machine usage is:

8 hours/day × 250 days/year = 2,000 hours/year

then:

20,000 / 2,000 = 10 years

But if the plant runs:

24/7

annual hours approach:

8,760 hours

and the same 20,000-hour rating corresponds to only about:

2.3 years.

Duty cycle matters.

Why Stroke Length Matters

Longer stroke means more rolling-contact travel per machine cycle.

Therefore, for the same number of cycles:

longer stroke consumes fatigue life faster in terms of hours.

A machine running:

100 mm stroke

will accumulate travel distance far more slowly than one running:

2,000 mm stroke

at the same cycles per minute.

Short-Stroke Applications Need Special Attention

THK warns that its standard nominal-life formula may not apply when:

stroke length ≤ twice the LM block length.

THK — Nominal Life

Short oscillating strokes can create operating conditions that are not represented well by normal full-recirculation fatigue assumptions.

If your machine uses:

very short reciprocation,
dithering,
small oscillatory motion,

consult the manufacturer.

What Is Modified Nominal Life?

Nominal life is based on defined reference conditions.

Real operating conditions can include:

vibration,
impact,
fluctuating load,
temperature,
raceway hardness,
multiple blocks mounted closely.

THK therefore provides a modified nominal life calculation incorporating correction factors.

Depending on the applicable guide, factors can include:

hardness factor,
temperature factor,
contact factor,
load factor.

These modify the effective capacity used in the life relationship.

Conceptual Modified-Life Relationship

For an applicable ball guide, the relationship may take the form:

L₁₀m = (α × C / P)³ × reference distance

where:

is a combined modification factor.

THK identifies applicable components such as:

fH = hardness factor,
fT = temperature factor,
fC = contact factor,
fW = load factor.

Use the model-specific manufacturer equation rather than assuming every product uses exactly the same factor set.

Load Factor and Real Machines

Theoretical calculated load does not always capture:

vibration,
shock,
unexpected impact,
operating uncertainty.

Manufacturer load-factor methods account for these realities.

A smooth, low-speed axis may justify a different factor than:

high-speed machinery,
equipment with impact,
vibrating machine tools.

Do not choose a correction factor arbitrarily.

Raceway Hardness Can Affect Life

Rolling-contact load ratings assume suitable hardened raceways.

THK notes that appropriate raceway hardness is required to achieve optimum load capacity and incorporates a hardness factor where relevant.

For normal profile rails, this is generally already controlled by the guide manufacturer.

It becomes especially relevant in linear-bearing systems where the machine itself provides part of the raceway.

Temperature Can Affect Life

High temperature can affect:

material hardness,
lubricant,
seals,
dimensional behavior.

Some manufacturer modified-life methods therefore apply temperature correction.

Do not use a standard-room-temperature life calculation unchanged for a specialized high-temperature application.

Contact Factor and Multiple Blocks

When multiple blocks are arranged close together, actual load sharing may not be perfectly equal.

THK includes a contact factor in applicable modified-life calculations because closely arranged blocks can experience nonuniform load distribution.

This reinforces an important point:

Four blocks do not necessarily give four times the life or capacity of one block.

Preload and Linear Guide Life

Preload intentionally creates internal rolling-element load.

That improves:

rigidity,
response under reversing forces.

But greater preload can reduce fatigue-life margin.

THK specifically requires preload to be considered in service-life calculations for applicable preload conditions, while Schaeffler likewise notes that preload adds to rolling-element loading.

So:

more preload ≠ more life.

Why Excessive Preload Can Shorten Life

Suppose an externally lightly loaded carriage is heavily preloaded.

The rolling contacts still experience internal stress even though the payload is small.

Fatigue damage depends on:

actual internal rolling-contact loading

not merely external payload.

Therefore, use only enough preload to achieve the required rigidity.

Rail Spacing Can Dramatically Increase Life

Suppose roll moment produces excessive carriage load.

For a simplified two-rail system:

F ≈ M / S

where:

M = roll moment,
S = rail spacing.

Increasing S reduces carriage reaction force.

Because ball-guide fatigue life varies with approximately the inverse cube of load, reducing carriage load through better rail spacing can dramatically increase calculated life.

Example: Geometry vs. Guide Size

Suppose one carriage currently carries:

6 kN

because the rails are too close together.

The guide has:

C = 30 kN

Ball life:

L = (30 / 6)³ × 50

L = 6,250 km

Now improve machine geometry so the carriage load drops to:

4 kN

Life:

L = (30 / 4)³ × 50

≈ 21,094 km

Guide size did not change.

Calculated life increased by more than:

3×

because machine geometry improved.

Block Spacing Can Do the Same Thing

For pitch or yaw moments:

F ≈ M / L

where L is effective block spacing.

Greater spacing reduces the reaction force required to resist the moment.

That can:

reduce carriage load,
increase static safety,
increase fatigue life,
reduce deflection.

Before increasing guide size, evaluate the support footprint.

Lowering the Center of Gravity Can Increase Life

Moment:

M = F × d

Reducing the distance d reduces moment.

Lowering a high payload can therefore reduce carriage reactions.

This may produce more life than simply installing a larger rail.

Long Blocks Can Increase Life

A long carriage generally offers greater:

dynamic rating C,
static rating C₀,
permissible moment capability

than the corresponding standard block in the same family.

If machine space permits, a long block may increase calculated life without requiring a larger nominal rail.

But compare the exact manufacturer ratings.

Larger Rail Size Can Increase Life

If calculated life remains insufficient after optimizing geometry, increasing rail size typically increases C.

Because C appears in the numerator and is raised to a power:

even a moderate increase in C can produce a large increase in calculated fatigue life.

Ball vs. Roller Life Should Not Be Chosen From Formula Alone

The roller exponent and rating basis differ from the ball relationship.

But do not conclude that roller guides automatically last longer.

Actual life depends on:

C,
P,
architecture,
preload,
machine geometry,
duty cycle.

A properly sized ball guide can easily exceed the required machine life.

Contamination Can Make Calculated Life Meaningless

The L₁₀ equation assumes rolling-fatigue failure.

A guide may instead fail prematurely from:

abrasive particles,
metal chips,
coolant contamination,
damaged seals.

A theoretically calculated:

50,000 km

life means little if contamination destroys the raceway in six months.

Use suitable:

seals,
scrapers,
covers,
lubrication.

Lubrication Is Essential to Achieving Life

Rolling contacts require an adequate lubricant film.

Poor lubrication can lead to:

wear,
heat,
surface damage,
premature fatigue.

Always consider lubrication as part of guide-life design rather than a separate maintenance afterthought.

Corrosion Can End Life Before Fatigue

Moisture and aggressive environments can damage:

raceways,
rolling elements.

Corrosion pits create local stress concentrations.

If corrosion is likely, consider:

suitable material,
protective treatment,
environmental protection.

Mounting Accuracy Affects Real Life

Misalignment can create unintended internal loading.

Examples include:

rails not parallel,
uneven mounting heights,
warped table,
poor base flatness.

These errors can heavily load one carriage even if the theoretical free-body calculation predicts equal loading.

Highly preloaded and highly rigid guides can be particularly sensitive to poor installation.

How Much Linear Guide Life Do You Need?

There is no universal target.

Determine:

machine expected service years,
hours per day,
days per year,
cycles per minute,
stroke,
planned rebuild interval.

Then convert those requirements to travel distance.

Required-Life Example

Machine must operate:

10 years

at:

16 hours/day

250 days/year

Required hours:

10 × 16 × 250

= 40,000 hours

Stroke:

0.75 m

Cycles:

6 reciprocations/min

Travel per hour:

2 × 0.75 × 6 × 60

= 540 m/h

= 0.54 km/h

Required guide travel:

40,000 × 0.54

= 21,600 km

Therefore, the selected system should provide adequate calculated life beyond:

21,600 km

after applying the appropriate design assumptions and manufacturer factors.

Work Backward to Required Dynamic Rating

You can also rearrange the ball-life equation.

Starting with:

L = (C / P)³ × 50

Then:

C = P × (L / 50)^(1/3)

This lets you estimate the dynamic rating required to meet a target life.

Required-C Example

Required life:

20,000 km

Equivalent load:

5 kN

Then:

C = 5 × (20,000 / 50)^(1/3)

C = 5 × 400^(1/3)

400^(1/3) ≈ 7.37

Therefore:

C ≈ 36.9 kN

A candidate guide would need an appropriate dynamic rating at least in that range before:

correction factors,
preload,
additional engineering margin

are considered.

This Is Why C/P Ratio Is So Useful

The life equation is fundamentally controlled by:

C/P

Increasing C helps.

Reducing P helps.

But reducing P through better machine geometry can often be more efficient than simply increasing rail size.

Complete Linear Guide Life Calculation Process

Step 1: Define the Required Machine Life

Determine:

hours,
years,
cycles,
required travel distance.

Step 2: Identify the Guide Type

Determine:

ball,
roller.

Step 3: Determine Dynamic Rating C

Use the exact candidate carriage catalog.

Step 4: Calculate Loads on Every Carriage

Include:

gravity,
acceleration,
deceleration,
process loads,
pitch,
yaw,
roll.

Step 5: Convert Directional Loads

Use the guide manufacturer's equivalent-load method.

Step 6: Determine Load for Every Operating Phase

Include every meaningful part of the machine cycle.

Step 7: Calculate Fatigue-Equivalent Average Load

Do not use arithmetic averaging unless the manufacturer specifically permits it for that load pattern.

Step 8: Account for Preload

Where required by the manufacturer.

Step 9: Apply Relevant Modification Factors

Consider:

vibration,
shock,
temperature,
hardness,
close block arrangement.

Step 10: Calculate Life for Every Carriage

Use the appropriate ball or roller equation.

Step 11: Identify the Shortest Carriage Life

That is generally the controlling guide-system life.

Step 12: Convert Distance to Hours

Use:

stroke,
cycles per minute.

Step 13: Compare With Required Machine Life

If insufficient, modify the design.

Step 14: Optimize Before Upsizing

Consider:

rail spacing,
block spacing,
lower center of gravity,
long blocks,
more appropriate carriage arrangement.

Step 15: Increase Guide Size if Needed

Then repeat the calculations.

Worked Ball-Guide Example

Consider a four-block machine table.

Candidate guide:

C = 35 kN per carriage

After full machine-cycle analysis, the most highly loaded block has:

Pm = 5.5 kN

Calculate L₁₀

L₁₀ = (35 / 5.5)³ × 50

C/P:

6.364

Cube:

≈ 257.7

Life:

≈ 12,885 km

Convert to Hours

Stroke:

0.8 m

Cycles:

5/min

Travel per hour:

2 × 0.8 × 5 × 60

= 480 m/hour

= 0.48 km/hour

Hours:

12,885 / 0.48

≈ 26,844 hours

Convert to Years

At:

2,000 operating hours/year

life is approximately:

13.4 operating years

before any additional manufacturer correction factors or real-world maintenance considerations.

What Happens if Load Increases by 20%?

Original load:

5.5 kN

New load:

6.6 kN

Life:

L = (35 / 6.6)³ × 50

≈ 7,455 km

Life fell from:

12,885 km

to about:

7,455 km

from only a 20% load increase.

This shows why accurate carriage-load calculation matters so much.

What Happens if C Increases by 20%?

Original C:

35 kN

New C:

42 kN

Load remains:

5.5 kN

Life:

L = (42 / 5.5)³ × 50

≈ 22,300 km

A moderate rating increase can dramatically affect life.

Again, the cubic relationship is powerful.

Common Linear Guide Life Calculation Mistakes

Mistake 1: Using C₀ Instead of C

C₀ is for static safety.

C is for fatigue life.

Mistake 2: Calculating From Total Payload

Use actual carriage loads.

Mistake 3: Dividing Load Equally Among Blocks

Moment loads often prevent equal sharing.

Mistake 4: Using Peak Load for the Entire Life Cycle

Peak load belongs in static checks; fatigue loading should reflect the actual duty cycle.

Mistake 5: Using Arithmetic Average Load

Rolling fatigue is nonlinear.

Mistake 6: Ignoring Acceleration and Deceleration

These can dominate carriage loading.

Mistake 7: Ignoring Preload

Internal preload can affect life.

Mistake 8: Comparing C Values With Different Rating Bases

Check 50 km vs. 100 km conventions.

Mistake 9: Assuming Calculated L₁₀ Is Guaranteed Service Life

It is a statistical fatigue-life rating.

Mistake 10: Ignoring Contamination

Real guides often fail from environmental damage before theoretical fatigue.

Mistake 11: Ignoring Lubrication

The life formula does not make poor lubrication harmless.

Mistake 12: Ignoring Short Stroke

Standard formulas may not apply to very short reciprocating motion.

Linear Automation USA's Perspective

At Linear Automation USA, we treat linear-guide life as the last major calculation in a chain, not as a catalog lookup.

The wrong sequence is:

payload → catalog C value → life formula

The better sequence is:

machine geometry → forces → moments → individual carriage loads → operating phases → equivalent average load → C/P → life

That distinction matters because linear-guide fatigue life is extraordinarily sensitive to load.

For a ball guide, a relatively small reduction in carriage load can produce a very large increase in calculated life.

That means we do not immediately move to a larger rail whenever life appears insufficient.

We first ask:

Why is the carriage load high?

If the answer is:

excessive roll moment, increase rail spacing where possible;
excessive pitch moment, evaluate block spacing;
high center of gravity, lower the load if possible;
insufficient local carriage capacity, evaluate a long block;
poor load sharing, examine guide arrangement and mounting structure.

Then we recalculate life.

We also distinguish:

theoretical rolling-fatigue life

from:

real machine service life.

A guide calculated for tens of thousands of kilometers can still fail early if the application has:

contamination,
inadequate lubrication,
corrosion,
misalignment,
severe shock.

A strong guide selection therefore combines:

fatigue calculation + static safety + rigidity + preload + mounting + environmental protection.

Linear Automation USA supports industrial profile rail systems from Schaeffler, SBC Linear, and WON Linear, including sizing, identification, replacement, and cut-to-length rail support.

Our rule is:

Calculate life from the most critical carriage's real operating load—not from machine payload or catalog capacity alone.

Frequently Asked Questions

What Is the Formula for Linear Guide Life?

For an applicable THK ball guide using a 50 km dynamic-rating basis:

L₁₀ = (C/P)³ × 50 km

For an applicable THK roller guide using a 100 km basis:

L₁₀ = (C/P)^(10/3) × 100 km.

What Does C Mean?

C is the basic dynamic load rating used for fatigue-life calculation.

What Does C₀ Mean?

C₀ is the basic static load rating used for peak-load/static-safety evaluation.

What Does P Mean?

P is the calculated equivalent load acting on the carriage for the applicable life calculation.

What Is L₁₀ Life?

L₁₀ is the nominal life that 90% of a population of identical bearings under identical conditions is expected to reach or exceed without rolling-fatigue flaking.

Why Does Linear Guide Life Change So Much With Load?

Because fatigue life varies with approximately the third power of C/P for ball guides and the 10/3 power for roller guides.

Should I Use Maximum Load to Calculate Life?

Not necessarily. Use maximum load for static-safety checks. For varying operating loads, use the manufacturer's fatigue-equivalent average-load method.

Can I Simply Average All Loads?

No. Arithmetic averaging can significantly overestimate life because rolling fatigue is nonlinear.

Does Preload Reduce Linear Guide Life?

Greater preload can reduce fatigue-life margin because it adds internal rolling-element load.

Does Rail Spacing Affect Life?

Yes, indirectly. Wider rail spacing can reduce carriage reaction loads from roll moments, which can greatly increase calculated life.

Does Block Spacing Affect Life?

Yes. Greater block spacing can reduce carriage reactions caused by pitch and yaw moments.

Do Ball and Roller Guides Use the Same Life Formula?

No. Their fatigue exponents and commonly used reference-distance conventions differ.

Why Are Some C Ratings Based on 50 km and Others on 100 km?

They use different reference-life conventions. Normalize the ratings before comparing them.

Can a Guide Reach Its Calculated Life Without Lubrication?

No meaningful fatigue-life expectation should assume inadequate lubrication. Manufacturer lubrication requirements remain essential.

Does Short Stroke Affect Life Calculation?

Yes. THK warns that its standard nominal-life formulas may not apply when stroke is less than or equal to twice the block length.

Need Help Calculating Required Linear Guide Life?

For a new application, document:

manufacturer or candidate guide series,
ball or roller type,
dynamic rating C,
moving mass,
carriage loads,
acceleration/deceleration,
external process forces,
rail spacing,
block spacing,
preload,
stroke,
cycles per minute,
operating hours per day,
operating days per year,
required machine years,
vibration/shock conditions,
environment.

For an existing machine, also provide:

complete rail number,
complete carriage number,
block quantity,
rail length,
photographs.

Contact Linear Automation USA with this information when evaluating the life or replacement of an industrial profile rail system.