Shaft Key and Keyseat Size (ANSI B17.1)
The band-table width and H/2 depth machinists mis-read.
Example
You enter
- Shaft diameter D (in) 1
- Transmitted torque (in-lb, 0 = geometry only) 1000
- Key / hub engagement length L (in, 0 = geometry only) 1.5
You get
- Standard key (W x H) 0.25
- Shaft keyseat depth (H/2) 0.125 in
- Key shear stress 5333
- Key bearing stress 10667
Details, formula, and sources
ANSI B17.1 sets the standard key width from the shaft-diameter BAND, not exactly D/4 -- a 1 in shaft (over 7/8 to 1-1/4) takes a 1/4 in square key, cut to a 0.125 in (H/2) shaft keyseat depth (over-cutting off the full key height weakens the shaft). Key stresses: shear = 2T/(D W L), bearing = 4T/(D H L). At 1,000 in-lb over a 1.5 in key the shear is 5,333 psi and bearing 10,667 psi (both well under a steel key); but a key longer than the hub adds no capacity -- a 1.0 in hub sets the working length, raising shear to 8,000 psi. Square-key model; the allowables and fit class govern.
key_width = standard width from the ANSI B17.1 shaft-diameter band; shaft_keyseat_depth = key_height/2; shear_stress = 2T/(D x W x L); bearing_stress = 4T/(D x H x L).
The ANSI B17.1 Keys and Keyseats standard key and keyseat sizing (Machinery's Handbook), by name; the material allowables and the fit class govern.
The ANSI B17.1 key-size bands and the key-stress relations are published in standard machine-design references; the torque and hub length come from the drive.
Estimate. AHJ and licensed professional govern.
Field names used by the API: shaft_diameter_in, torque_in_lb, key_length_in, key_width_in, shaft_keyseat_depth_in, shear_stress_psi, bearing_stress_psi
- Band-table width the key width comes from the shaft-diameter band, not exactly D/4ANSI B17.1
- H/2 depth the shaft keyseat is cut to half the key height; over-cutting weakens the shaftANSI B17.1
- Hub limits length a key longer than the hub adds no capacity; the hub length is the effective lengthkey-stress model