Which key standard applies?

Metric duties look up DIN 6885-1 parallel keys by shaft diameter band. Imperial duties use ASME B17.1 square-key screening sizes. Manual b×h overrides either table.

What does key check Pass mean?

Pass means key shear and bearing unities are ≤ 1.0 and engagement L ≥ L_min = max(L_shear,min, L_bearing,min) under the stated S.F.

Does this cover shaft bending from overhang?

No. This is pure torsion screening. Significant overhang moments need combined (von Mises) stress and keyseat Kt ≈ 2–3 fatigue review.

Shaft Power, Torque & Parallel Key Sizing Calculator (DIN 6885 / ASME B17.1)

Engineering Reference & ASME Code Basis

1. Core Formula & Variable Definitions

DIN 6885-1 — Drive type fastenings without taper; parallel keys · ISO R773 — Rectangular and square parallel keys and their keyways · ASME/ANSI B17.1-1967 (R2013) — Keys and keyseats · ANSI/AGMA 6001-E08 — Design guide for shafts and keys

T = P·9549/n (N·m) · T = HP·63025/n (in·lbf)

τ_key = 2T/(d·b·L) ≤ 0.577·F_y/S.F. · σ_b = 2T/(d·h₁·L) ≤ F_y/S.F.

DIN 6885-1 · ISO R773 · ASME/ANSI B17.1 · ANSI/AGMA 6001 — pure torsion screening

Standard DIN 6885-1Hero T + Pass/Failh₁ ≈ 0.5·hτ_allow 0.577·Fy/SF

Transmitted torque from shaft power and speed. Parallel-key shear and bearing (compressive) stress use engagement length L with h₁ ≈ 0.5·h. Allowables use von Mises shear factor 0.577·Fy/S.F. and Fy/S.F. Metric key sizes follow DIN 6885-1 by shaft diameter band; imperial uses ASME B17.1 square-key screening sizes. Pure torsion only — bending from overhang and keyseat Kt fatigue are out of scope.

P (Shaft / motor power) — Transmitted power — kW (metric) or HP (imperial).
n (Rotational speed) — Operating speed (rpm).
T (Transmitted torque) — T = P·9549/n (N·m) or HP·63025/n (in·lbf).
d (Shaft diameter) — Shaft OD at the keyseat (mm or in).
b, h (Key width and height) — Parallel key cross-section from DIN 6885-1 (metric) or ASME B17.1 square key (imperial), or manual override.
h₁ (Keyseat depth in shaft) — Bearing contact depth approximated as h₁ ≈ 0.5·h for compressive stress.
L (Key engagement length) — Effective parallel-key length in the hub (mm or in).
F_y (Key / shaft yield strength) — Ambient screening yield — S45C/AISI 1045 ≈ 345 MPa; SCM440/AISI 4140 ≈ 655 MPa; SUS304 ≈ 205 MPa.
S.F. (Service / safety factor) — Design factor on allowables (typical 1.5–3.0).

2. Screening rules & default duty

Default metric duty: 45 kW · 1750 rpm · Ø50 mm · S45C shaft/key · DIN 6885 14×9 mm · L = 50 mm · S.F. = 2.0. Pass when key shear and bearing unities ≤ 1.0 and engagement L ≥ L_min = max(L_shear,min, L_bearing,min).

TorqueT = P·9549/n

Metric N·m from kW and rpm. Imperial uses T = HP·63025/n (in·lbf).

Key allowablesτ = 0.577·Fy/SF · σ_b = Fy/SF

von Mises shear factor on key yield; bearing allowable equals Fy/S.F.

Keyseat depth h₁≈ 0.5·h

Compressive stress uses half key height (h₁ ≈ 0.5·h). Diagram shows shaft seat h₁ and hub seat h₂ (DIN t2 when available).

Recommended L band0.9·d ≤ L ≤ 1.5·d

DIN 6885-1 typical hub engagement band — not a hard pass/fail gate.

Out of scopeBending · Kt fatigue

Overhang bending moment, combined von Mises shaft stress, and keyseat stress concentration (Kt ≈ 2–3) are not evaluated.

Quick Reference Lookup Table

DIN 6885-1 parallel key sizes by shaft diameter band (mm) — screening lookup in this app
Shaft d (mm)	b × h (mm)	t1 / t2 (mm)
Over 22 to 30	8 × 7	4.0 / 3.3
Over 30 to 38	10 × 8	5.0 / 3.3
Over 38 to 44	12 × 8	5.0 / 3.3
Over 44 to 50	14 × 9	5.5 / 3.8
Over 50 to 58	16 × 10	6.0 / 4.3
Over 58 to 65	18 × 11	7.0 / 4.4
Over 65 to 75	20 × 12	7.5 / 4.9
Over 75 to 85	22 × 14	9.0 / 5.4
Over 85 to 95	25 × 14	9.0 / 5.4
Over 95 to 110	28 × 16	10.0 / 6.4
Over 110 to 130	32 × 18	11.0 / 7.4
Over 130 to 150	36 × 20	12.0 / 8.4

Bands follow DIN 6885-1 Form A screening (dMin < d ≤ dMax). Confirm OEM / finished keyseat drawings for final selection. Imperial duties use ASME B17.1 square-key sizes by shaft diameter.

3. Applicability & allowable stress limits

Ambient yield screening for carbon / alloy / stainless shaft and key steels. Temperature derating, notch sensitivity, and surface finish factors are not applied. τ_allow = 0.577·Fy/S.F.; σ_b,allow = Fy/S.F.

Group / Regime	Range / Condition	Limit / Criterion	Engineering Notes
S45C / AISI 1045 class	—	Fy ≈ 345 MPa (50 ksi)	Default shaft and key material. Ambient min-yield screening — confirm mill cert for tempered condition.
SCM440 / AISI 4140 QT class	—	Fy ≈ 655 MPa (95 ksi)	Higher-strength alloy shaft option. Key often remains S45C/1045 — check galvanic / hardness mismatch.
SUS304 / SS304	—	Fy ≈ 205 MPa (30 ksi)	Austenitic stainless screening yield. Expect longer L_min vs carbon steel at the same torque.
Service regime	—	—	Pure torsion parallel-key screen only. Pump/motor overhang bending and reversing fatigue need separate Kt-based review.

Code Applicability & Safety Boundaries

Not a certified AGMA / OEM shaft design — field screening against DIN 6885 / ASME B17.1 geometry and basic stress formulas.
Do not substitute for detailed shaft FEA or OEM coupling hub charts when bending or shock loads dominate.

4. Step-by-Step Worked Example

Field VerificationShow

Worked example — 45 kW · 1750 rpm · Ø50 mm · S45C

Screen a motor shaft at 45 kW, 1750 rpm with a 50 mm diameter S45C shaft and DIN 6885 14×9 mm parallel key, L = 50 mm, S.F. = 2.0.

Power P:45 kWSpeed n:1750 rpmShaft d:50 mmKey b × h:14 × 9 mm (DIN 6885)Key length L:50 mmMaterials:S45C shaft & key · Fy = 345 MPaS.F.:2.0

Transmitted torque

Formula: T = P·9549/n

T = 45·9549/1750

Result:T = 245.5 N·m

Key allowables

Formula: τ_allow = 0.577·Fy/SF · σ_allow = Fy/SF

τ_allow = 0.577·345/2 · σ_allow = 345/2

Result:τ_allow ≈ 99.5 MPa · σ_allow = 172.5 MPa

Key stresses at L = 50 mm

Formula: τ = 2T/(d·b·L) · σ_b = 2T/(d·h₁·L) · h₁ = 0.5·h

h₁ = 4.5 mm · τ = 2·245.5·1000/(50·14·50) · σ_b = 2·245.5·1000/(50·4.5·50)

Result:τ_key ≈ 14.0 MPa (14% unity) · σ_b ≈ 43.7 MPa (25% unity)

Minimum key length

Formula: L_min = max(L_shear,min, L_bearing,min)

L_bearing,min = 2·T·SF·1000/(d·h₁·σ_allow) governs

Result:L_min ≈ 25.3 mm · Pass (L = 50 mm ≥ L_min)

Open /45kw-1750rpm-d50mm-s45c-metric for the live default case.

Conclusion: For the default 45 kW · 1750 rpm · Ø50 mm · S45C duty, transmitted torque is 245.5 N·m with key check Pass. Governing minimum key length is about 25.3 mm (bearing), well below the 50 mm engagement.

5. How to size shaft torque and a parallel key

1
Enter power and speed
Set shaft power (kW or HP) and rotational speed (rpm) to compute transmitted torque T.
2
Enter shaft diameter and materials
Set shaft OD and select shaft/key steels (S45C/1045, SCM440/4140, or SUS304).
3
Select key size
Use DIN 6885 (metric) or ASME B17.1 (imperial) auto lookup, or enter b×h manually. Set engagement length L and S.F.
4
Read torque and key check
Hero shows T and Pass/Fail. Summary shows L_min and shear/bearing unities. Increase L or key size if Fail.

6. Frequently Asked Questions & Technical References

Show

Metric: T (N·m) = P(kW)·9549/n. Imperial: T (in·lbf) = HP·63025/n.