Lathe Operations
What this domain tests
Lathe Operations tests setup, workholding, tool geometry, turning, facing, boring, parting, threading, taper turning, and measurement on the lathe. The exam emphasizes safe spindle practice and correct relationship between speed, feed, and tool position.
Core rules and concepts
- Never leave a chuck key in the chuck. Check that the workpiece is held securely, remove the chuck key, and engage the correct spindle range before starting.
- Set tool height on center. A tool above center rubs; below center can dig in. Use a center gauge for threading tools and set the compound to 29.5° for unified threads.
- Inch turning speed: RPM = (4 × cutting speed in ft/min) / workpiece diameter in inches. Roughing uses higher feed and depth; finishing uses lower feed and a sharp tool.
- For threading, set the quick-change gearbox to the required TPI, engage the half-nut on the same thread-dial mark, and use the compound for infeed. For a 1/2-13 UNC thread, pitch = 1/13 = 0.0769 in; compound infeed approximately 0.75 × pitch = 0.0577 in.
- Parting: use a sharp parting tool set on center, plenty of coolant, and a slow speed. Keep the tool perpendicular to the work and do not force it.
- Taper turning: use the compound, taper attachment, or offset tailstock; calculate the included or half angle from the drawing rather than guessing.
Worked example
Turn a 2.000 in diameter mild steel shaft at 100 ft/min. RPM = (4 × 100) / 2.000 = 200 rpm. Reasoning: the same inch constant gives a safe starting speed; a finishing pass might use 0.005 in/rev feed, while roughing could use 0.010-0.015 in/rev with a deeper cut. Always confirm with the tool manufacturer's data.
Traps that cost marks
Leaving the chuck key in place; setting the compound to 30° instead of 29.5°; engaging the half-nut at any dial mark; parting without coolant; and measuring a hot part. These are classic lathe mark-losers.