1. Definition of a Jig: A
Jig is a specialized tool that performs two primary functions:
• It
holds and locates the workpiece in a fixed position.
• It
guides the cutting tool during the operation using bushings.
2. Why Jigs are used in Drilling: In
Drilling (as well as related operations like reaming and tapping), the tool is relatively slender and can "wander" from the intended center point. A drill jig uses hardened steel bushings to physically guide the drill bit to the exact coordinate required, eliminating the need for manual marking (layout) on every individual part.
3. Jigs vs. Fixtures:
• Fixtures (used in Milling, Turning, and Grinding) only hold and locate the work. They do
not guide the tool. Because milling and turning tools are typically much larger and more rigid, or the path is controlled by the machine's carriage, a physical guide like a bushing is not used.
• In
Turning, the work rotates while the tool is fixed in a tool post; therefore, a jig is not applicable.