Turning = the workpiece rotates while a single-point tool removes material on a lathe.

Lathe Operations

• Turning — straight/conical/curved/grooved (shafts, pins).
• Facing — flat end face (or O-ring grooves).
• Drilling — produce a hole (often followed by boring).
• Boring — enlarge an existing hole.
• Parting (cutting off) — cut a piece from the end.
• Threading — external/internal threads.
• Knurling — patterned roughness (knobs).

Turning Formulas

$N$ = spindle speed (rpm), $f$ = feed (mm/rev), $D_o$/$D_f$ = original/final diameter, $D_{text{avg}} = (D_o + D_f)/2$, $l$ = length of cut.

Feed rate (tool linear speed):

$v = f N \quad [\text{mm/min}]$

Surface (cutting) speed:

$V = \pi D_o N\ (\text{max}) = \pi D_{\text{avg}} N\ (\text{avg}) \quad [\text{m/min}]$

Depth of cut:

$d = \frac{D_o - D_f}{2}$

Cutting time:

$t = \frac{l}{v} = \frac{l}{f N}$

Material removal rate:

$\text{MRR} = \pi D_{\text{avg}}\,d\,f\,N \quad [\text{mm}^3/\text{min}]$

Torque and power:

$\text{Torque} = \frac{F_c D_{\text{avg}}}{2}, \qquad \text{Power} = \text{Torque}\times\omega, \quad \omega = 2\pi N$

Three tool forces: cutting $F_c$ (downward, supplies energy), thrust/feed $F_t$ (longitudinal), radial $F_r$ (pushes the tool away). Usual practice: roughing cuts (high feed/depth, high MRR) then a finishing cut (low feed/depth, good finish).

Lathe Components

Bed, carriage + apron, tool post, headstock (motor/spindle/chucks), tailstock (supports the other end, holds drills), feed rod. Specified by swing (max diameter), distance between centers, and bed length (e.g. 360 / 760 / 1830 mm).

Workholding: chucks (3- or 4-jaw), collets (split tapered bushing; grip small cross-sections within 0.125 mm of nominal), face plates (irregular parts).

CNC lathes: computer-controlled, often with turrets (several tools each); repeatable accuracy, less-skilled labor, low–medium volume.

High-Speed & Ultraprecision Machining

• High-speed ranges: high 600–1800 m/min, very high 1800–18,000, ultrahigh > 18,000 m/min. Spindles up to ~40,000 rpm (auto industry ~15,000). Most heat leaves in the chip → workpiece stays near ambient (no thermal warping).
• Ultraprecision: single-crystal diamond tool (edge radius a few nm), nanometer depths; finish in tens of nm; tool cooled by liquid nitrogen (~−120°C); copper/Al alloys, silver, gold, Ni, acrylics.

Thread Cutting

Threads by forming (rolling — most threads) or cutting. Lathe thread cutting uses a shaped tool moved by the lead screw; tapping cuts internal threads. Slower tool advance → finer thread. Skill-intensive and slow → mostly replaced by rolling/CNC. Allow threads to terminate before a shoulder (stress concentration).

Boring, Drilling, Reaming, Tapping

• Boring: enlarge internal profiles; the boring bar must be stiff (high $E$, e.g. tungsten carbide) to avoid deflection/chatter; vertical boring machines for large parts.
• Drilling: main hole-making process; holes are slightly oversize; may be followed by reaming/honing.
  • Twist drill (two flutes guide chips & fluid), step, core (enlarge a hole), counterbore/countersink, center, spot, spade, gun drill (deep holes, depth/diameter 300:1+).
• Drilling machines: drill press; large radial drills (column-to-spindle up to ~3 m); CNC three-axis with turrets.
• Reaming: make a hole more accurate & smooth; removes ~0.2 mm (soft) / 0.13 mm (hard) on diameter. Most accurate sequence: centering → drilling → boring → reaming.
• Tapping: internal threads with a multi-tooth tap (commonly two-flute spiral-point).