Counter-Milled Pin Chambers: Overcut Chambers Trapping Spool Pin Lips
Engineering Overview: Engineering analysis of counter-milled (undercut) pin chambers in brass cylinder bodies, creating physical ledges that deadlock spool pins.
Technical & Engineering Specifications
| Standard | EN 1303:2015 Key Security Grade 6 |
|---|---|
| Ledge Depth | 0.20 mm Annular Locking Lip |
| Chamber Geometry | Precision Counter-Milled / Undercut Chamber Bores |
| Security Synergy | Pairs with Spool and Mushroom Top Driver Pins |
The Counter-Milling Principle
Standard straight-bored pin chambers allow spool pins to slide smoothly when counter-rotated. Counter-Milled Pin Chambers introduce internal horizontal ledges.
Physical Ledge Deadlocking
- Internal Undercut: An annular lip (0.2 mm step) milled inside the chamber wall at the shear line.
- Permanent Binding: When a spool pin enters a false set, its wide lip drops into the counter-milled ledge and physically binds, resisting all picking tools.
Frequently Asked Engineering & Selection Questions
Q1: How does counter-milling pin chambers improve lock security?
It creates internal ledges in the chamber walls that physically trap the lips of spool pins when picked, making picking nearly impossible.