Reading checks and safeties
What a check compares, how the banner and its colours read, what a safety factor means and what to do when a check fails.
A result on its own does not say whether a design is good enough. A check compares it with a limit: a maximum deflection, a minimum life, a required safety. Each module lists its checks in the banner at the top of its results.
The checks banner
The headline counts the checks:
- All 7 checks pass, or The check passes when there is only one.
- 2 of 7 checks fail, or The check fails.
- No checks yet, when no limit is set. Set limits to get pass/fail checks.
Below the headline is one row per check: its name and its value against its limit.
| Row | Reads as |
|---|---|
| Shaft deflection 22 / 50 µm | A maximum: 22 µm found, at most 50 µm allowed. |
| Minimum life 3 073 537 / min 20 000 h | A minimum: 3 073 537 h found, at least 20 000 h required. |
Each row has one of three marks:
| Mark | Meaning |
|---|---|
| Tick | The check passes with margin. |
| Exclamation mark (warning) | The check passes, but the value uses more than 85 % of its limit. In the bolt, fit and key modules: the safety is less than 15 % above its minimum. |
| Cross | The check fails. |
The 85 % threshold is a reminder, not a rule. A check at 90 % passes. Whether that margin is enough depends on how well you know the loads and the material.
Utilisation
Every check has a utilisation: how much of its limit the design uses.
- For a maximum (deflection, stress, tilt, damage), utilisation = value / limit.
- For a minimum (life, safety, critical speed), utilisation = limit / value.
Whether a check passes comes from comparing the value with its limit, sign included: a margin of −17° against a minimum of 0° fails. Against a limit of 0 or below (the ball screw's margin to the groove edge, or a limit you set to 0) a ratio means nothing, so the utilisation is 100 % at the limit, from 0 to 100 % inside it and up to 200 % beyond it, and the check's message gives no percentage.
Below 100 % the check passes. The command line prints it after each check, for example "(44%)". The Overview lists every component with its governing check and its utilisation, so you can see at once which part limits the design.
Safety factors
Many checks are on a safety factor: the ratio of what a part can take to what it gets. A safety of 1.5 means the part could carry 1.5 times the load (or stress) before reaching the failure criterion of the standard.
Each standard defines its own safety, so safeties of different modules are not comparable:
| Module | Safety | Default minimum in the app |
|---|---|---|
| Bearings | Static safety (ISO 76) | Set per bearing; s0 ≥ 1–2 is typical for normal service |
| Shaft strength | Fatigue and static safety (DIN 743) | Set by you; 1.2 is typical when the loads are well known |
| Gear pairs | Pitting SH, tooth root SF (ISO 6336) | SH 1.0, SF 1.4 |
| Gear pairs, scuffing | Flash SB, integral SintS | 2.0 and 1.8 |
| Worm pairs | Contact, root, wear, thermal (DIN 3996) | 1.0, 1.1, 1.1, 1.1 |
| Bolted joints | Yield, fatigue, surface pressure, slip, shearing (VDI 2230) | 1.0, 1.2, 1.0, 1.2, 1.1 |
| Fits | Slip, yield | 1.5, 1.1 |
| Keys and splines | Pressure | 1.0 |
| Springs | Fatigue (EN 13906) | 1.1 |
| Ball screws, guides | Static safety; minimum life | 2; 20 000 h |
These defaults are common minima from the standards or from practice. They are a starting point. Your company's rules, the consequences of a failure and how well the loads are known decide the right value. Change a limit in the module's inputs. A limit that is not set is not checked.
Some checks work with a damage sum or a utilisation instead of a safety. A weld group passes when its utilisation and its damage sum are at most 1. The FKM shaft strength check requires its degrees of utilisation aBK and aSK to be at most 1, with the safety factors already inside them.
Lives
A life check compares a rating life with the life you require, in hours (bearings, ball screws, guides) or in cycles. A bearing life is a statistical value: the basic L10 life is the life that 90 % of a large group of identical bearings reach or exceed. A life ten times the requirement is not ten times as safe in the sense of a safety factor. See Rating life (ISO 281).
When a check fails
- Read the row. It names what failed and by how much.
- Open the module and find the result behind it. The results column usually shows where the value occurs, for example "at x = 200 mm".
- Change the design, not the limit, unless the limit was wrong. Typical levers:
| Failing check | Typical changes |
|---|---|
| Shaft deflection or tilt | Larger diameter where the bending moment is high; supports closer to the load; a shorter overhang |
| Shaft stress or strength | Larger diameter; larger fillet radius at shoulders; a better material or surface treatment |
| Bearing life | A bearing with a higher C; a cleaner or more viscous lubricant (higher κ); a lower load or speed |
| Bearing static safety | A bearing with a higher C0; a lower peak load |
| Bearing minimum load | More load or a preload, so the elements roll instead of skidding |
| Gear pitting or root | Wider face; larger module or centre distance; a harder material; a lower application factor if justified |
| Bolt fatigue or slip | A larger thread or a higher property class; better tightening (a lower αA); more bolts |
| Critical speed | A stiffer shaft or supports; less overhung mass |
- Watch the other checks. Making one part stiffer often moves load elsewhere.
Warnings and notes
Besides checks, the solver reports notes: warnings about the model, such as a preset's estimated internal geometry, a value outside the range a standard covers, or a simplification. They do not fail the design, but read them. A note can mean that a result is less reliable than it looks.
When the inputs cannot be solved, the results show Can't solve yet with each reason and a hint. Nothing is computed from invalid inputs, so a missing check is never shown as passing.
Unlimited values
A part without load has no fatigue: its life and safety are "unlimited". A check against an unlimited value passes. A bearing the shaft leaves unloaded still fails its minimum-load check, because unloaded rolling elements skid.