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Milling brass and bronze: end mill speeds and feeds

Published carbide end mill SFM and chip load for free-cutting brass, naval brass and bronzes from Harvey Tool, Kyocera SGS and 6GTools, plus alloy machinability, tool geometry and worked examples.

Brass is the easy one, as long as you know which brass you have. The published surface speeds for carbide end mills spread wider here than in any steel: Harvey Tool's general table allows 800-1500 SFM for yellow, high-lead and red brass and 600-1000 SFM for naval brass and high-silicon bronze [1]. Kyocera SGS's general-purpose end mill catalog is far more conservative at 485 SFM (388-582) for profiling and 350 SFM (280-420) for slotting copper alloys up to 140 Bhn, its group for aluminum bronze, C110 copper and Muntz brass [2]. 6GTools lists 400 SFM for brass and bronze with uncoated carbide [3], and Travers gives 400-800 SFM for carbide and 100-200 for HSS [4].

Surface speed, carbide end mills

ChiploadPro's end mill calculator doesn't cover brass yet. Use these tables and the formulas RPM = SFM × 3.82 ÷ D and IPM = RPM × flutes × IPT [1].

Chip load by diameter

Inches per tooth, solid carbide. SGS profile values assume radial engagement up to 0.5 × D on 2-flute tools (0.25 × D on 3 and 4 flutes) for the general-purpose series, and up to 0.3 × D for the high-shear series [2]. At lighter radial cuts the real chip gets thinner than the programmed feed, see chip thinning [9].

Which brass matters more than which tool

Leaded free-cutting brass, C36000 (also sold as "360 brass"), is the material other metals get rated against. Mueller Brass lists its machinability at 100% [5]. In the Copper Development Association's production-scale tests, medium-leaded brass C34000 came in at 66, naval brass C46400 at about 50, the same as 2011-T3 aluminum, and 12L14 leaded steel at 21. In those tests C36000 ran about five times the production rate of leaded steel for an eight-hour tool life [7].

The bronzes are a different story. Kyocera SGS drops beryllium copper, manganese bronze and tin bronze to 235 SFM for profiling and 190 for slotting, less than half its brass figures [2]. If the stock isn't marked, treat it as the harder group until the chips tell you otherwise.

Tool geometry and coolant

Brass likes a neutral cutting edge. Mueller's C36000 data lists a 0-10° back rake and 10-15° clearance for milling cutters [5]. Harvey Performance says 2- and 3-flute tools are the usual choice in non-ferrous materials: 2 flutes for chip clearance, 3 for finishing and high-efficiency toolpaths [8]. For coolant, Mueller's data sheet calls for light mineral (paraffin) oil or 20:1 water-soluble oil and warns that sulfurized oils will stain the parts. It also says to use maximum speed and minimum feed for finish cuts [6].

Worked example: 1/2" 2-flute profile in C36000

SGS general purpose, profile: 485 × 3.82 ÷ 0.5 = 3,705 RPM, and 3,705 × 2 × .0020 = 14.8 IPM, the same numbers printed in the catalog [2]. Radial width up to 0.25" (0.5 × D) and axial depth up to 0.75" (1.5 × D) [2].

Power check at 0.25" wide × 0.5" deep: 0.25 × 0.5 × 14.8 = 1.85 in³/min. The CDA paper quotes a tool maker's unit power of 0.50 HP per in³/min for free-cutting brass [7], so about 0.9 HP at the cutter before motor and drive losses. Brass is rarely a horsepower problem. RPM usually runs out first.

The same tool at Harvey's low end for yellow brass: 800 × 3.82 ÷ 0.5 = 6,112 RPM, and 6,112 × 2 × .003 = 36.7 IPM [1]. That's 2.5 times the SGS feed. Prove the program at the catalog figure for your tool, then move up.

Worked example: 1/2" 2-flute slot

SGS slot: 350 × 3.82 ÷ 0.5 = 2,674 RPM, 2,674 × 2 × .0020 = 10.7 IPM, up to 1 × D deep with 2 flutes, 0.5 × D with 3 and 0.4 × D with 4 [2].

FAQ

What SFM should I run a carbide end mill at in brass?

Published starting points for solid carbide in brass run from 800-1500 SFM for yellow, high-lead and red brass and 600-1000 SFM for naval brass in Harvey Tool's general table, 485 SFM (388-582) for profiling and 350 SFM (280-420) for slotting copper alloys up to 140 Bhn in Kyocera SGS's general-purpose catalog, 400 SFM for uncoated carbide from 6GTools, and 400-800 SFM from Travers. The spread is wide, so start near the low end and go up from the chips and finish.

What chip load should I use for a 1/2" end mill in brass?

For a 1/2" carbide end mill in brass the published chip loads are .003 in/tooth (Harvey Tool), .0020 for profiling with SGS general-purpose end mills, .0026 with SGS high-shear end mills, and .0042 from 6GTools, which shares its aluminum chip loads with brass.

Is all brass easy to machine?

No. Leaded free-cutting brass C36000 is the machinability benchmark at 100. In the Copper Development Association's ASTM E618 tests, medium-leaded brass C34000 rated 66 and naval brass C46400 about 50. Bronzes such as beryllium copper, manganese bronze and tin bronze get much lower surface speeds in Kyocera SGS's catalog (235 SFM profiling vs. 485-590 for brass).

Choosing flute count Aluminum guide

Related guides

• Aluminum end mill speeds and feeds
• Chip thinning: why light cuts need more feed
• Choosing flute count for end mills
• Runout: the hidden feed killer

Tooling for this job

• 2-flute carbide end mills for non-ferrous metals
• C360 brass bar stock
• Cutting fluid

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Sources

1. [1] Harvey Tool, General Machining Guidelines (carbide end mills, non-ferrous table)
2. [2] Kyocera SGS, 2023 Global Catalog: General Application End Mills, copper alloys speed & feed, pp. 322-323 (PDF)
3. [3] 6GTools, Carbide end mill speeds & feeds (uncoated carbide, brass/bronze row)
4. [4] Travers Tool, Industrial Milling Speed & Feed Calculator (SFM by material table)
5. [5] Mueller Brass Co., C36000 Free Cutting Brass (machinability table)
6. [6] Mueller Industries, Alloy C36000 Free Cutting Brass data sheet (PDF, hosted by Dixon Valve)
7. [7] Copper Development Association, Comparative Machinability of Brasses, Steels and Aluminum Alloys: CDA's Universal Machinability Index (PDF)
8. [8] Harvey Performance, 5 Questions to Ask Before Selecting an End Mill
9. [9] Harvey Performance, How to Combat Chip Thinning