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Cutter & Feed Libraries
How CNC programs know how fast to spin and feed every cutter, in every material.
CNC milling uses cutter and feed libraries to know how fast to spin and feed each cutter in every kind of steel.
Every cutter has a speed it likes to run and a feed it likes to take, and both change with the material. A cutter library stores each tool's diameter, flutes, length and coating. A feed library stores the cutting speed and chip load for each material, from aluminum to hardened tool steel.
When a CNC program is built, the library supplies the spindle RPM and feed rate for each tool and material, so cutters last longer, finishes come out clean and parts come off the machine the same way every time.
Surface speed (SFM)
How fast the cutting edge moves across the material, in feet per minute.
Chip load
How thick a chip each cutting edge takes, in inches per tooth.
Spindle speed (RPM)
How fast the cutter turns, worked out from SFM and diameter.
Feed rate (IPM)
How fast the cutter moves through the part, in inches per minute.
| Material | Starting SFM | Chip load vs. mild steel |
|---|---|---|
| Aluminum 6061 | 1000 | 130% |
| Brass / bronze | 600 | 110% |
| Mild steel 1018 | 450 | 100% |
| Alloy steel 4140 (annealed) | 350 | 90% |
| Gray cast iron | 350 | 100% |
| Stainless 304 | 300 | 80% |
| Tool steel A2 / D2 (annealed) | 250 | 80% |
| Hardened tool steel 45–55 HRC | 150 | 50% |
| Plastics (Delrin, UHMW) | 600 | 150% |
Starting points for solid carbide end mills. Adjust for coating, tool stick-out, machine rigidity and coolant.
| Cutter diameter | In/tooth, mild steel |
|---|---|
| 1/16" | 0.0003 |
| 1/8" | 0.0006 |
| 3/16" | 0.0009 |
| 1/4" | 0.0012 |
| 3/8" | 0.0018 |
| Cutter diameter | In/tooth, mild steel |
|---|---|
| 1/2" | 0.0025 |
| 5/8" | 0.0030 |
| 3/4" | 0.0035 |
| 1" | 0.0040 |
Larger cutters take thicker chips. Multiply by the material factor in the material library.
RPM = SFM × 3.82 ÷ diameterIPM = RPM × flutes × chip loadDeff = 2 × √( depth × (D − depth) )A ball nose cuts on a smaller diameter at shallow depths, so it needs more RPM to reach the same surface speed.
Links open the supplier's own site. Their data is for their tools; use it with the cutter you actually run.