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Linear Guide (LM Guide) Life Calculator — Rated Life, Hours & Static Safety (ISO 14728-1)

Governing standard: ISO 14728-1· ISO 14728-1 rated life · catalog fH/fT/fC/fW modifying factors · 50 km (ball) / 100 km (roller) basis

The MechanixCalc linear guide life calculator computes the rated life and static safety of a linear-motion guide (LM guide / linear rail) to ISO 14728-1 — the standard for the rated life of linear motion rolling bearings. Enter the guide type (ball or roller), the catalog basic dynamic load rating C, the applied dynamic equivalent load per block P, and the duty factors, and the tool returns the nominal life in kilometres, the life in operating hours, and the static safety factor in a single pass.

It is built for machine-design engineers selecting linear guides for positioning stages, transfer axes, gantries and automation. The nominal life follows the catalog convention — the exponent and reference distance depend on the rolling element (3 and 50 km for ball, 10/3 and 100 km for roller) — with the hardness (fH), temperature (fT), contact (fC) and load/speed (fW) modifying factors applied. The static safety factor guards against permanent raceway indentation (brinelling), and a branded PDF report carries the full method for design review.

What this calculator does

  • ISO 14728-1 nominal rated life in kilometres for ball (exponent 3, 50 km basis) and roller (10/3, 100 km) guides
  • Life in operating hours from the stroke length and reciprocation frequency
  • Static safety factor fS = (fH·fT·fC·C0)/P0 with a recommended-floor check (brinelling guard)
  • Hardness (fH), temperature (fT), contact (fC) and load/speed (fW) modifying factors
  • Basis guard — states the 50/100 km reference distance so the dynamic load rating C can't be mis-plugged
  • Optional target-life check for an explicit pass/fail verdict
  • Branded PDF engineering report with the full ISO 14728-1 method shown

Method & formulas

Nominal rated life (ISO 14728-1)

ISO 14728-1 defines the rated life as the travel distance that 90% of a group of identical guides will reach before the first sign of rolling-contact fatigue. It depends on the ratio of the basic dynamic load rating C to the applied dynamic equivalent load P, raised to the life exponent p, and scaled by a reference distance. For a ball guide p = 3 and the reference is 50 km; for a roller guide p = 10/3 and the reference is 100 km — the convention on which the THK/HIWIN/NSK/NB/MiSUMi catalogs publish C. The hardness (fH ≤ 1), temperature (fT ≤ 1) and contact (fC ≤ 1) factors reduce the effective capacity, while the load/speed factor fW ≥ 1 raises the effective load for vibration and speed.

The single most common error is mixing rating bases: a C rated on a different reference distance mis-scales the life directly. The calculator states the basis it used so the rating can be confirmed.

Nominal life
L = ( (fH·fT·fC)/fW · C/P )^p × basis

where L = nominal life (km); C = basic dynamic load rating (kN); P = applied dynamic equivalent load per block (kN); p = 3 (ball) or 10/3 (roller); basis = 50 km (ball) or 100 km (roller); fH, fT, fC ≤ 1; fW ≥ 1.

Life in hours

A life in kilometres becomes a maintenance figure once the travel rate is known. The life in operating hours follows from the stroke length and the number of reciprocations per minute — each reciprocation covers two strokes.

Life in hours
Lh = L·10⁶ / (2·ℓs·n₁·60)

where Lh = life (hours); L = nominal life (km); ℓs = stroke length (mm); n₁ = reciprocations per minute.

Static safety factor

Fatigue life is a running check; the static safety factor is a survival check. It compares the basic static load rating C0 (reduced by the same hardness, temperature and contact factors) against the peak static or moment load the block ever sees. Below about 1 the raceway can take a permanent dent (brinelling); catalogs recommend a floor of 1.0–1.3 for smooth duty and 2.0–3.0 where impact or vibration is present. The load/speed factor fW is not applied to the static check.

Static safety factor
fS = (fH·fT·fC·C0) / P0

where fS = static safety factor (target ≥ 2 with impact); C0 = basic static load rating (kN); P0 = applied static equivalent load per block (kN). fW is NOT applied to the static rating.

Worked example

Estimate the ISO 14728-1 nominal life of a ball LM guide with a basic dynamic load rating C = 28 kN carrying a dynamic equivalent load P = 4 kN per block, at the reference load factor fW = 1.

Given

  • Guide typeBall (p = 3, basis 50 km)
  • Dynamic load rating C28 kN
  • Applied load P4 kN / block
  • Load factor fW1 (reference)

Result

  • Nominal rated life17,150 km
  • Life in hours (500 mm @ 30/min)≈ 9528 h
  1. Compute the C/P ratio: C/P = 28 kN / 4 kN = 7.
  2. Raise to the ball life exponent (p = 3): 7³ = 343.
  3. Scale by the ball reference distance (50 km): L = 343 × 50 = 17,150 km.
  4. For the life in hours at, say, a 500 mm stroke and 30 reciprocations/min: Lh = 17,150 × 10⁶ / (2 × 500 × 30 × 60) ≈ 9528 hours.

This uses the ball-guide 50 km basis; confirm your catalog C is quoted on that basis. In practice apply a load factor fW > 1 for vibration/speed (the calculator defaults to 1.5), which lowers the life. This example is illustrative — verify against your actual catalog ratings and duty.

Frequently asked questions

Which standard does this linear guide calculator use?

It follows ISO 14728-1 — the standard for the rated life of linear motion rolling bearings — with the standard catalog modifying factors (fH hardness, fT temperature, fC contact, fW load/speed). The nominal-life form and the 50 km (ball) / 100 km (roller) reference distance follow the dominant catalog convention (THK, HIWIN, NSK, NB, MiSUMi), on which those catalogs publish the basic dynamic load rating C. The factor values are catalog convention layered on the standard, and are documented in the tool.

Why is the reference distance 50 km for ball guides but 100 km for roller?

The basic dynamic load rating C is defined as the load giving a specified reference life, and that reference distance is set by convention — 50 km for ball guides and 100 km for roller guides in the major catalogs. The load rating you read from a catalog is on that basis, so the life formula uses the matching basis for the guide type. Mixing the two changes the life by a factor of two, so the calculator states the basis it used.

How do I convert linear guide life from km to hours?

Lh = L × 10⁶ / (2 × ℓs × n₁ × 60), where L is the nominal life in km, ℓs is the stroke length in mm, and n₁ is the number of reciprocations per minute. The factor of two accounts for the block travelling the stroke in both directions each reciprocation. Provide the stroke and frequency and the calculator returns the life in hours alongside the kilometres.

What static safety factor should a linear guide have?

The static safety factor fS = (fH·fT·fC·C0)/P0 compares the static load rating against the peak static or moment load. Below about 1 the raceway can be permanently indented (brinelled), which the tool flags as a failure. Catalogs recommend a floor of 1.0–1.3 for smooth duty and 2.0–3.0 where impact or vibration is present. The load factor fW is not applied to the static check.

Is the linear guide calculator free?

It runs during a free 30-minute preview with no sign-up, and a free 14-day account trial unlocks every calculator on the platform with no credit card. The branded PDF report and saved calculations are included in the trial and every paid plan.

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