This article outlines a precise method for cutting Schlage C keyways (the common 5-pin configuration) using a milling machine. This technique offers a potentially more accurate alternative to traditional key cutting machines, ensuring a perfect fit and minimizing lock wear. This method was developed for rekeying Schlage locks on rental properties, requiring frequent lock changes.
Modifying the Tools for Key Cutting
The process begins with modifying two standard tools: a 90-degree countersink and a parallel.
Countersink Modification: A 3/8″ diameter 90-degree countersink with a point (available from suppliers like McMaster-Carr) is required. The point needs to be slightly flattened on sandpaper. Factory-cut keys have a flat of .035″. A slightly wider flat of around .055″ allows for greater tolerance on the X-axis (lateral) placement of the cuts. Precision on the Z-axis (depth) is critical.
Parallel Selection: A parallel a few thousandths narrower than the key blank is necessary for precise clamping. If a suitable parallel isn’t available, machining one is an option, though it requires careful work due to its thinness.
The Key Cutting Process
Setup and Zeroing: The key blank is clamped in the vise with the bow facing left and then coated with Dykem layout fluid. An edge finder is used to locate the shoulder of the key and zero the X-axis. The quill is centered and adjusted for backlash before zeroing again.
Positioning and Cutting: The X-axis is moved .100″ away from the shoulder, the modified countersink is inserted, and the Z-axis is cranked up to zero. The quill is lowered until the flattened tip lightly touches the key. After clamping the quill, the X-axis is moved to the position for the first cut (.231″). The Z-axis is then adjusted to the correct depth for that cut, and the vise is moved along the Y-axis to execute the cut. Subsequent cuts are made by adjusting the X and Z axes.
Cut Depth and Spacing: Schlage keys use specific depths corresponding to different pin heights. Each cut is spaced .156″ apart, starting at .231″ from the shoulder. The following chart provides the necessary Z-axis depths for each Schlage pin number and the corresponding “key area” measurement (the distance between the bottom of the cut and the bottom of the key).
Finishing Touches
Comparison with Factory Cut: The mill-cut key profile exhibits slightly wider bases at the bottom of each cut compared to a factory-cut key. This wider base provides increased tolerance, preventing issues when cutting adjacent deep and shallow cuts. However, extreme variations in adjacent cut depths (e.g., a 0 cut next to a 9 cut) should be avoided as they can strain the lock mechanism.
Peak Filing: The final step involves filing down the sharp peaks between the cuts. This reduces friction and wear on the lock’s internal components, ensuring smooth key insertion and withdrawal and prolonging the lock’s lifespan. This results in a key that functions smoothly and minimizes wear on the lock.
This milling Machine Key Cutting technique provides a precise and controlled method for creating Schlage keys. The accuracy and adjustability of the process make it a viable alternative to dedicated key cutting machines, particularly for applications requiring frequent key duplication or replacement.
