Key Bitting Depths and Root Radii: Preventing Key Blade Stress Fractures
Engineering Overview: Technical guide on key bitting step increments, root cut radii, and blade stress concentration to prevent key breakage in commercial cylinders.
Technical & Engineering Specifications
| Standard | DIN 18252 / BHMA A156.5 |
|---|---|
| Root Radius | R 0.45 mm Stress Relief Radius |
| Angle of Cut | 90° to 105° Included Angle |
| Key Material | Nickel-Silver (CuNi12Zn24) or Hardened Brass |
| Bitting Increments | 0.50 mm / 0.60 mm Step Depths |
CNC Key Cutting Geometry
The profile of key cuts directly affects key insertion smoothness and blade structural integrity.
Critical CNC Milling Parameters
- Root Cut Radius ($R$): Key bitting cuts must incorporate a precision corner radius ($R = 0.40\text{ mm}$ to $0.60\text{ mm}$) rather than sharp 90° corners, reducing stress concentration ($K_t$) and preventing key snapping.
- Bitting Step Increment: Standard commercial systems utilize 0.50 mm or 0.60 mm depth steps across 10 depth positions.
- Root Flat Width: A flat bottom ($0.80\text{ mm}$) ensures bottom pins seat securely on the cut center.
Frequently Asked Engineering & Selection Questions
Q1: Why must key bitting cuts have rounded root radii?
Sharp 90-degree cuts concentrate mechanical stress, causing keys to crack and snap in half under normal turning torque.