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Copper Speeds and Feeds
Guide · Updated October 28, 2026
Pure copper is soft and conducts heat well, but it is gummy: it smears, builds up on the edge and throws long stringy chips and big burrs. Free-machining grades such as tellurium copper (C145) cut far more like brass. The keys are a very sharp, high-rake tool, a positive chip load and plenty of lubricant.
Check bus bar and electrode sizes
Copper grows noticeably with heat (about 9.4 millionths per inch per °F). Let it cool, then verify your mic against gage blocks before the finish pass. The free Gage Block Calculator builds the stack.
Step by step
- Identify the grade: C110 (ETP) and C101 (OFE) are pure and gummy; C145 tellurium and C147 sulfur copper are free-machining; beryllium copper is hard and dust is toxic, so follow its own safety rules.
- Choose sharp, high-rake tools: Polished uncoated carbide or ZrN/DLC-coated tools with sharp edges, 2 or 3 flutes for milling; ground (not honed) inserts for turning.
- Pick a starting SFM: Pure copper with carbide: roughly 300–600 SFM; with HSS about 80–150 SFM. Tellurium copper can run near brass speeds.
- Feed with a positive chip load: Around 0.001–0.003 in per tooth for 1/4–1/2 in cutters. Too light a feed rubs and smears.
- Lubricate generously: Flood coolant or a cutting oil reduces built-up edge; avoid sulfurized oils on copper if staining matters.
- Plan for burrs: Use climb milling, a final light pass and a deburr step; pure copper rolls big burrs.
- Hold gently: Copper is soft; use soft jaws and moderate clamping so you do not dent or bow the part.
Worked example
Milling a C110 bus bar with a 3/8 in 3-flute uncoated carbide end mill at 400 SFM: RPM = 3.82 × 400 ÷ 0.375 = 4,075 RPM. At 0.0015 in per tooth, feed = 4,075 × 3 × 0.0015 = 18.3 IPM. Rough with 0.020 in left, then finish at the same chip load. If the part was warm at 90 °F when measured and should be 2.000 in at 68 °F, the growth is 2.000 × 0.0000094 × 22 = 0.0004 in, so let it cool before sizing.
Copper vs brass
Brass chips break into small pieces and the tool barely notices it. Pure copper does the opposite: long continuous chips and edge buildup. If the drawing allows, a free-machining copper grade saves a lot of trouble.
Common problems
Built-up edge and torn finish mean the tool is dull, the rake is too low or there is not enough lubricant. Chatter on thin bus bar means poor support. Big burrs mean conventional milling or a dull edge; switch to climb and a fresh tool.
Tips
- Compare: brass speeds and feeds for free-machining alloys.
- Tools: carbide end mill basics.
- Burrs: deburr and break edges.
FAQ
What SFM for copper with carbide?
About 300–600 SFM for pure copper as a starting point; tellurium copper can go faster.
Why does copper gum up?
Pure copper is very ductile, so it welds to the edge. Sharp high-rake tools and lubricant help.
Should I use coated tools on copper?
Uncoated polished carbide or ZrN/DLC coatings work well; avoid aluminum-reactive or rough coatings.
Is copper dust dangerous?
Pure copper is low hazard, but beryllium copper dust is toxic; machine it wet with proper controls.
How do I reduce burrs?
Climb mill, keep tools sharp and take a light final pass.
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