CNC Turning Material Selection & Tolerance Control Guide: Key Machining Points for Stainless Steel, Aluminum, Titanium, and PEEK

Choosing the right material and controlling tolerances are critical to successful CNC turning. Below are the key machining considerations for four common materials.

  Stainless Steel (e.g., 303, 304, 316): Requires rigid setups and sharp tooling due to work hardening. Use low speeds and consistent feed rates to prevent surface hardening. For tolerances, expect ±0.01 mm with proper cooling. Chip breaking is difficult — employ high-pressure coolant.

  Aluminum(e.g., 6061, 7075): Easy to machine with high speeds and aggressive feeds. Achievable tolerances can reach ±0.005 mm. Key issues include built-up edge (BUE) and chip welding. Use polished carbide tools and mist lubrication. For tight bores, allow for thermal expansion.

 Titanium(e.g., Grade 5 Ti-6Al-4V): Requires sharp tools, low speeds, and high feed rates to avoid heat accumulation. Use climb milling and high-pressure coolant. Tolerances around ±0.01 mm are typical. Maintain rigid work-holding to combat chatter and spring-back.

  PEEK (Polyether ether ketone): High-performance plastic needing sharp, polished tooling to prevent melting. Use moderate speeds with air blast rather than coolant. Tolerances can be ±0.02 mm but parts will expand with heat. Allow for stress-relief pre-machining to avoid warping. Watch for burr formation on exit edges.

In summary, select tool geometry, speeds, and cooling strategies based on material hardness and thermal behavior. For tight tolerances, always consider material-specific expansion, tool deflection, and fixturing rigidity. Test cuts and in-process measurement are recommended for high-precision batches.