Thermal Expansion Coefficients for CNC Materials
CTE for 22 CNC materials in µm/m·°C with the temperature range each value covers, plus worked examples of what the differences do to fits and inspection.
Coefficient of thermal expansion (CTE) by material and temperature range
| Material (grade) | CTE (µm/m·°C) | Temperature range | Engineering significance | Source |
|---|---|---|---|---|
| Aluminum 1060 (commercially pure) | 23.6 | 20–100 °C | Highest CTE among common CNC metals; busbar and heat-sink designs must allow expansion gaps | ASM Handbook Vol. 2 via matmake.com |
| Aluminum 6061-T6 | 23.6 | 20–100 °C | Most machined aluminum alloy; CTE is temper-independent (O, T4, T6 and T651 all 23.6) | ASM Handbook Vol. 2, 10th ed.; MIL-HDBK-5J |
| Aluminum 6061-T6 | 24.6 | 20–200 °C | Elevated-temperature mean rises ~4%; use a range-specific CTE above 150 °C | MIL-HDBK-5J; ASM Handbook Vol. 2 |
| Aluminum 7075-T6 | 23.6 | 20–100 °C | Aerospace grade; same CTE as 6061 despite twice the yield strength — simplifies mixed-alloy fixture design | matmake.com; arcuscnc.com |
| Copper C11000 (ETP) | 17.0 | 20–100 °C | Busbar and connector material; CTE mismatch vs aluminum (23.6) drives joint fatigue in bimetallic lugs | fabdigit.com (C11000-O properties) |
| Copper C11000 (ETP) | 17.0 | 20–300 °C | Mean CTE over a wide range; manufacturer datasheet value | jtcopper.com C11000 datasheet |
| Brass C36000 (free-cutting) | 20.5 | 20–100 °C (approx.) | Highest-machinability copper alloy; CTE between copper and aluminum — relevant for brass inserts in aluminum housings | mechcodex.com C36000 thermal table |
| Carbon steel AISI 1045 (annealed) | 11.6 | 0–100 °C | Baseline shaft and gear steel; CTE about half of aluminum — Al-to-steel bolted joints develop 0.12 mm of differential per 100 mm at ΔT = 100 °C | theworldmaterial.com AISI 1045 physical properties |
| Carbon steel AISI 1045 (annealed) | 12.3 | 0–200 °C | Elevated-temperature mean; rises with the temperature range | theworldmaterial.com AISI 1045 |
| Alloy steel AISI 4140 (normalized) | 12.3 | 20–100 °C | High-strength shaft and axle steel; CTE similar to 1045 — interchangeable in thermal-stress calculations | ASM Handbook Vol. 1; metalzenith.com |
| Stainless steel 304/304L | 17.3 | 0–100 °C | Austenitic stainless expands ~44% more than carbon steel; critical for heat-exchanger tube-to-tubesheet joints | jnalloys.com CTE comparison table |
| Stainless steel 316/316L | 15.9 | 0–100 °C | Lower CTE than 304 despite the similar austenitic structure (molybdenum addition); preferred for marine piping expansion design | jnalloys.com CTE comparison table |
| Stainless steel 17-4PH (H900) | 10.8 | 0–100 °C | Martensitic PH steel; CTE closest to carbon steel among stainless grades — ideal for precision aerospace fittings mating with steel structures | xometry.com; alloy-materials.com (20–100 °C) |
| Titanium Ti-6Al-4V (Grade 5) | 8.6 | 20–100 °C | Lowest CTE of common structural metals; good match to CFRP (0–2) in aerospace hybrid joints | arcuscnc.com CTE comparison |
| Titanium Ti-6Al-4V (Grade 5) | 8.8 | 20–100 °C (approx.) | Alternate published value; the difference sits within measurement uncertainty (±2%) | mechcodex.com Ti-6Al-4V properties |
| Tool steel P20 (pre-hardened, 28–32 HRC) | 11.7 | 20–100 °C | Mould base steel; CTE must match the insert steels to avoid thermal stress cracking in injection moulds during thermal cycling | ASM Handbook Vol. 1; firstmold.com (P20 context) |
| Tool steel H13 (hot-work, 44–52 HRC) | 12.0 | 20–200 °C | Die-casting and forging die steel; runs at 500–650 °C surface temperature, so the elevated-range CTE matters for die insert fits | ASM Handbook Vol. 1; metalzenith.com |
| Delrin / POM (acetal homopolymer) | 110 | 23–60 °C | About 5× steel; plastic-to-metal press fits loosen as temperature rises — design the interference at the maximum operating temperature | firstmold.com; DuPont Delrin 500P datasheet |
| Nylon 6/6 (unfilled, dry-as-molded) | 80 | 23–60 °C | Moisture absorption adds hygroscopic expansion on top of the thermal term; 50% RH raises the effective dimensional change ~0.2% | DuPont Zytel 101L datasheet; ASM Handbook Vol. 21 |
| PEEK (unfilled, e.g. Victrex 450G) | 47 | 23–100 °C | Lowest CTE among unreinforced engineering plastics; approaches aluminum at elevated temperature — viable for metal replacement in thermal-cycling environments | makerstage.com (citing Victrex); criterionprecision.com (45–55) |
| PEEK (30% glass-filled, GF30) | 27 | 23–100 °C | Glass reinforcement cuts CTE ~43%; chosen when dimensional stability under thermal cycling is critical | makerstage.com PEEK grade comparison (Victrex) |
| ABS (general purpose, unfilled) | 90 | 23–60 °C | High CTE limits use in precision assemblies; acceptable for consumer enclosures with generous clearance | firstmold.com; Cycolac/Terlux datasheets |
How to read this table. Where two sources disagree, both rows are listed (Ti-6Al-4V appears at 8.6 and 8.8). Temperature ranges are quoted as published and are not normalized to one band — always use the CTE row whose range covers your actual temperature span.
When the Difference Becomes a Dimension
Five calculations from practice, each using ΔL = α × L × ΔT with values taken from the table above. They are the reason two materials with different CTE cannot be treated as interchangeable in a precision assembly.
| Case | Calculation | Result | Design response |
|---|---|---|---|
| 6061-T6 housing (CTE 23.6) bolted to a 1045 steel base (CTE 11.6), 200 mm bolt pattern, ΔT = 50 °C | ΔL(Al) = 23.6 × 10⁻⁶ × 200 × 50; ΔL(steel) = 11.6 × 10⁻⁶ × 200 × 50 | 0.236 mm vs 0.116 mm — 0.120 mm differential | With only 0.1 mm of bolt clearance the joint binds at ΔT = 50 °C. Use slotted holes, clearance ≥ 0.3 mm or compliant washers; for precision fixtures, build aluminum-to-aluminum or steel-to-steel. |
| Steel structure (CTE 12.0) bolted directly to a CFRP panel (CTE ~1.0 in the fibre direction), 300 mm span, ΔT = 80 °C | (12.0 − 1.0) × 10⁻⁶ × 300 × 80 | 0.264 mm relative slip per cycle | A Ti-6Al-4V insert (CTE 8.6) cuts the mismatch to 7.6 µm/m·°C on both sides and reduces differential movement ~30% — the reason titanium fittings dominate composite-joint aerospace designs. |
| Delrin bushing (CTE 110) press-fitted into a steel housing (CTE 11.6): 25 mm OD, 0.05 mm interference at 20 °C, service at 80 °C | ΔL(POM) = 110 × 10⁻⁶ × 25 × 60; ΔL(steel) = 11.6 × 10⁻⁶ × 25 × 60 | 0.165 mm vs 0.017 mm — 0.148 mm of interference lost (−0.098 mm, i.e. clearance) | The press fit becomes a slip fit at 80 °C. Calculate interference at maximum operating temperature, retain POM mechanically (snap rings, knurling), or switch to PEEK (CTE 47) or glass-filled PEEK (CTE 27). |
| A 500 mm 6061 part machined at 30 °C shop temperature, inspected at 20 °C (ISO 1 reference temperature) | 23.6 × 10⁻⁶ × 500 × 10 | 0.118 mm — reads 500.000 mm at 30 °C, 499.882 mm at 20 °C | For ±0.05 mm work that error is 2.4× the tolerance band: soak parts to 20 °C ± 1 °C before final inspection, or apply in-process compensation. |
| P20 mould base (CTE 11.7) carrying an H13 core insert (CTE 12.0), 100 mm insert diameter, ΔT = 60 °C, 0.02 mm designed clearance | 12.0 × 10⁻⁶ × 100 × 60; 11.7 × 10⁻⁶ × 100 × 60 | 0.072 mm vs 0.070 mm — clearance grows only 0.002 mm | P20 to H13 is thermally compatible (0.3 µm/m·°C mismatch). A beryllium-copper insert (CTE 16.6) against P20 loses 0.029 mm of clearance at the same ΔT — design BeCu inserts with a growth allowance. |
How to Use These Numbers
- CTE here is µm/(m·°C), equal to 10⁻⁶/K or ppm/°C. Pick the row whose temperature range matches the application — the same alloy publishes different means over different spans (6061: 23.6 over 20–100 °C, 24.6 over 20–200 °C).
- Heat treatment does not change aluminium CTE: 6061 reads 23.6 µm/m·°C in every temper (O, T4, T6, T651). Only the temperature range moves the effective value.
- Where sources disagree, both values are kept: Ti-6Al-4V appears at 8.6 and 8.8 µm/m·°C, a spread inside typical measurement uncertainty (±2%). For 304 stainless we use 17.3 — one calculator table shows 10.8, which is the 17-4PH value and a data-entry error.
- Plastics CTE depends strongly on filler, crystallinity and moisture. The Nylon 6/6 row is dry-as-molded (80); at 50% RH equilibrium the effective dimensional change rises ~0.2% on top of the thermal term.
- The inspection trap: parts grow with cutting heat and shrink on the CMM. A 300 mm 6061 part cut at 40 °C shrinks 0.14 mm by the time it reaches 20 °C — measure after a thermal soak, or budget the shift into the tolerance.
Frequently Asked Questions
How much does a 200 mm aluminum 6061 bar grow from 20 °C to 60 °C?
About 0.19 mm. ΔL = 23.6 × 10⁻⁶ × 200 × 40 = 0.189 mm.
About 0.19 mm. ΔL = 23.6 × 10⁻⁶ × 200 × 40 = 0.189 mm.
Why do my aluminum parts measure undersized after CNC machining?
Thermal contraction from cutting heat. A 300 mm 6061 part cut at 40 °C shrinks 0.14 mm by 20 °C (23.6 × 10⁻⁶ × 300 × 20). Soak the part to 20 °C before the final measurement.
Thermal contraction from cutting heat. A 300 mm 6061 part cut at 40 °C shrinks 0.14 mm by 20 °C (23.6 × 10⁻⁶ × 300 × 20). Soak the part to 20 °C before the final measurement.
What is the CTE difference between aluminum and stainless steel 304?
6.3 µm/m·°C (23.6 vs 17.3). Over 100 mm at ΔT = 50 °C that is 0.032 mm of differential movement.
6.3 µm/m·°C (23.6 vs 17.3). Over 100 mm at ΔT = 50 °C that is 0.032 mm of differential movement.
Can I press-fit a Delrin bushing into a steel housing for an 80 °C application?
Not with interference alone. POM CTE (110) is 9.5× steel (11.6): a 0.05 mm interference at 20 °C on a 25 mm diameter becomes clearance around 50 °C. Use mechanical retention, or switch to glass-filled PEEK (CTE 27).
Not with interference alone. POM CTE (110) is 9.5× steel (11.6): a 0.05 mm interference at 20 °C on a 25 mm diameter becomes clearance around 50 °C. Use mechanical retention, or switch to glass-filled PEEK (CTE 27).
Which metal has the lowest thermal expansion for precision fixtures?
Titanium Ti-6Al-4V at 8.6 µm/m·°C — lower than any common steel (11.6–12.3) and less than half of aluminum (23.6). For an ultra-low expansion structure, Invar (FeNi36) at 1.2 µm/m·°C is the extreme option but costs 10–20× more.
Titanium Ti-6Al-4V at 8.6 µm/m·°C — lower than any common steel (11.6–12.3) and less than half of aluminum (23.6). For an ultra-low expansion structure, Invar (FeNi36) at 1.2 µm/m·°C is the extreme option but costs 10–20× more.
How much does a 1-meter steel beam expand with a 40 °C rise?
About 0.46 mm for carbon steel 1045 (11.6 × 10⁻⁶ × 1000 × 40 = 0.464 mm). For 304 stainless, 0.69 mm — the reason long structures need expansion joints.
About 0.46 mm for carbon steel 1045 (11.6 × 10⁻⁶ × 1000 × 40 = 0.464 mm). For 304 stainless, 0.69 mm — the reason long structures need expansion joints.
Does heat treatment (T6 vs T4) change the CTE of aluminum 6061?
No. CTE is 23.6 µm/m·°C in every temper (O, T4, T6, T651). It is set by the aluminium lattice, not by the precipitate population; only the temperature range changes the effective value.
No. CTE is 23.6 µm/m·°C in every temper (O, T4, T6, T651). It is set by the aluminium lattice, not by the precipitate population; only the temperature range changes the effective value.
What CTE should I use for PEEK in a medical device at body temperature?
Use 47 µm/m·°C (unfilled, 23–100 °C range). At ΔT = 17 °C (20 → 37 °C) a 50 mm component grows only 0.040 mm — inside a typical ±0.025 mm machining tolerance if it is measured at 20 °C.
Use 47 µm/m·°C (unfilled, 23–100 °C range). At ΔT = 17 °C (20 → 37 °C) a 50 mm component grows only 0.040 mm — inside a typical ±0.025 mm machining tolerance if it is measured at 20 °C.
Standards & Sources
- ASM Handbook Vol. 2, 10th ed. (1990) — aluminum alloy CTE values and temper independence
- MIL-HDBK-5J (U.S. DoD, 2003) — temperature-dependent CTE for 6061 (20–100/200/300/400 °C)
- ASM Handbook Vol. 1 — AISI 4140 = 12.3; P20 = 11.7; H13 = 12.0 µm/m·°C
- DuPont Delrin 500P and Zytel 101L datasheets — POM 110 µm/m·°C (23–60 °C), Nylon 6/6 80 µm/m·°C (dry-as-molded)
- Victrex PEEK data via makerstage.com — unfilled 47, GF30 27 µm/m·°C; criterionprecision.com gives 45–55
- jnalloys.com CTE comparison — 304/304L = 17.3, 316/316L = 15.9 µm/m·K (0–100 °C)
- xometry.com and alloy-materials.com — 17-4PH = 10.8 µm/m·°C (20–100 °C)
- arcuscnc.com — Ti-6Al-4V = 8.6; matmake.com (ASM data) — aluminum alloy table; mechcodex.com — C36000 = 20.5, Ti-6Al-4V = 8.8
- theworldmaterial.com — AISI 1045 = 11.6 (0–100 °C) and 12.3 (0–200 °C); fabdigit.com — C11000 = 17 (20–100 °C); jtcopper.com — C11000 = 17.0 (20–300 °C)
- Where sources conflict, both rows are listed and the discrepancy is documented in the usage notes
Related Pages
- /wiki/reference/material-density/ — Sibling quick table: density of the same materials for weight and cost
- /wiki/reference/standard-tolerances/ — General tolerances and IT grades — the band your CTE shift is compared against
- /wiki/materials/aluminum/ — Aluminum alloys for CNC machining in detail
- /wiki/tooling/titanium-machining-guide/ — Titanium machining: why its low CTE and low conductivity both shape the process