Feed rate & chip load for Tool steel (O1 / A2 / D2, annealed)
Tool steel (O1 / A2 / D2, annealed) takes about 0.0015–0.0035 in/tooth (0.038–0.089 mm) of chip load on a 1/2″ carbide end mill, scaling down with diameter. A 1/4″ 2-flute cutter then feeds roughly 5.1–12 in/min.
Chip-load bands are starting points · scale with radial engagement and defer to your cutter’s data
Tool steel (O1 / A2 / D2, annealed) chip load by end-mill diameter
| Diameter | Chip load in/tooth | Chip load mm/tooth |
|---|---|---|
| 1/8″ 3.17 mm | 0.00038–0.00088 | 0.0095–0.022 |
| 3/16″ 4.76 mm | 0.00056–0.0013 | 0.014–0.033 |
| 1/4″ 6.35 mm | 0.00075–0.0018 | 0.019–0.044 |
| 3/8″ 9.52 mm | 0.0011–0.0026 | 0.029–0.067 |
| 1/2″ 12.7 mm | 0.0015–0.0035 | 0.038–0.089 |
| 3/4″ 19 mm | 0.0023–0.0053 | 0.057–0.13 |
Carbide end mills, starting bands anchored to published 1/2″ values and scaled ~linearly with diameter. Below ~0.0003 in/tooth the edge rubs instead of cutting.
Chip load is the star input — get it roughly right and the rest follows. Too little and the tool rubs and work-hardens the cut; too much and you snap flutes. These bands are a safe place to start; your cutter’s datasheet, radial engagement and rigidity move the real number.
Setting feed for Tool steel (O1 / A2 / D2, annealed)
Speeds shown are for the annealed condition. Once hardened, conventional milling gives way to grinding or hard-turning with CBN.
Why chip load scales with diameter
A small end mill is fragile, so it takes a tiny bite per tooth; a big one can take a much larger one. That is why the table above climbs with diameter — roughly 0.001″ per tooth for every 1/4″ of diameter is the shop rule of thumb, which is what the numbers here follow. Feed rate itself then comes from vf = n × fz × z: multiply the spindle speed by chip load and flute count.
Thin-chip rubbing — the mistake that kills tools
It feels safe to slow the feed down, but dropping chip load below about 0.0003–0.0005″ per tooth stops the edge from cutting and makes it rub instead. Friction spikes, heat goes into the tool, and in Tool steel (O1 / A2 / D2, annealed) that either work-hardens the surface or burns the edge. If a cut sounds like a squeal rather than a shear, the feed is usually too low, not too high.
Turning and drilling feeds
Milling feed is per tooth; turning and drilling feed is per revolution (in/rev or mm/rev), because a single-point turning tool or a two-flute drill advances once per turn. Typical turning feeds run ~0.005–0.020 in/rev for roughing and finer for finishing; drill feed scales with drill diameter. The per-tooth numbers here are for milling — don’t apply them directly to a lathe.
Need the spindle speed first? Tool steel (O1 / A2 / D2, annealed) cutting speed & RPM
References
- Machinery’s Handbook — “Cutting Speeds and Feeds”: feed-per-tooth and feed-per-revolution guidance.
- Tool-manufacturer chip-load charts (diameter- and flute-specific) — the authority for your exact cutter.
Last reviewed: 2026-07 · Calculation method & assumptions