Skills · skill
Turning on a Lathe
Metalwork · Intermediate
- Difficulty
- Intermediate
- Done When
- The part measures within tolerance along its length, the surface finish is even, and the tool made chips, not dust.
- Tools
- Lathe, three-jaw chuck, carbide-insert or HSS tools, live centre, calipers and a micrometer, cutting oil, brush for chips.
- Category
- Metalwork
- Summary
- Spinning a bar and moving a cutting tool along it to make round parts to a hundredth of a millimetre — shafts, bushes, threads.
Safety
No gloves, no loose sleeves, no jewellery — the chuck will take a hand. Chips are hot and sharp; brush, never grab. Remove the chuck key every single time.
Steps
Grip the stock with as little stick-out as the job allows; face the end.
Set the tool tip exactly on centre height — a scrap of shim under a rule against the stock tells you.
Set speed from cutting speed ÷ (π × diameter); feed 0.1–0.2 mm per rev.
Rough down leaving 0.5 mm; measure; take a finishing cut with a lighter feed.
Sneak up on the size: cut, measure, cut.
Deburr and chamfer.
The Science
The tool shears a chip off the surface; the geometry — rake angle, relief, nose radius — sets how it cuts and how it finishes. Cutting speed is surface metres per minute, so a bigger bar turns slower; carbide runs three times faster than high-speed steel. Depth of cut times feed is how fast metal comes off; heat goes mostly into the chip, which is why it turns blue.
How It Fails
Chatter — a rippled surface — from a long tool overhang or a thin part. Taper from a misaligned tailstock. A part that walks out of the chuck. A tool that rubs instead of cutting when below centre.
Referenced by
element
equation
machine
Open on the Skills shelf — the interactive card, the filters, and everything alongside it.