Why Starting Values Matter More Than Perfect Values
Most machining productivity is won or lost at the parameter-setting stage. A carbide insert running 20% below its ideal cutting speed will frequently deliver three to four times less tool life per edge, while the same insert pushed 20% too fast can collapse within minutes through plastic deformation or catastrophic flank wear. The gap between “good enough” and “optimized” cutting data is where thousands of machine hours are wasted every year.
The problem for most shops is not a lack of data — every major manufacturer publishes extensive cutting parameter tables. Sandvik Coromant, Iscar, Tungaloy, Mitsubishi Materials, Seco and Korloy all provide starting values in their catalogues and online tools. The real problem is that the data is scattered across hundreds of grade-specific pages, expressed in different formats, and often optimized for each brand’s own insert geometries. This guide consolidates realistic starting values for coated carbide inserts across all six ISO 513 material groups, then explains how to adjust them for your actual conditions.
How to use this reference: find your material group, note the recommended cutting speed (Vc), feed per revolution (fn) and depth of cut (ap), then apply the adjustment rules in the later sections for interrupted cuts, tool overhang, and workpiece hardness. Treat every value here as a starting point for the first test cut, not a final answer.
Understanding the ISO 513 Material Classification
The ISO 513 standard divides machinable materials into six groups identified by color codes. Every insert grade on the market is rated against these groups, so the classification is the foundation of all cutting data.
| ISO Group | Color Code | Typical Materials | Key Machining Challenge | Preferred Cutting Media |
|---|---|---|---|---|
| P — Steel | Blue | 1018, 1045, 4140, 42CrMo4, tool steel (annealed) | High temperature at the rake face; crater wear | CVD-coated carbide |
| M — Stainless | Yellow | 304, 316, 17-4 PH, duplex 2205 | Work hardening; built-up edge; adhesion | PVD-coated carbide, sharp edges |
| K — Cast Iron | Red | Grey GG25, ductile GGG50, vermicular CGI | Abrasive wear; edge chipping on scale | CVD-coated carbide, cermet |
| N — Non-ferrous | Green | 6061-T6, 7075-T6, copper, brass, plastics | Built-up edge; long chips; high speeds | Uncoated fine-grain carbide, PCD |
| S — Superalloys | Brown | Ti-6Al-4V, Inconel 718, Waspaloy, Hastelloy | Extreme heat concentration; notch wear | Fine-grain PVD carbide, ceramic, CBN |
| H — Hardened Steel | Grey | Steels 45–68 HRC, chilled iron | Very high hardness; edge strength limits | CBN, coated carbide (up to ~55 HRC) |
Two practical points deserve emphasis. First, the groups overlap: many modern multilayer grades cover two or three groups at once — Tungaloy’s AH725, for example, is rated for both stainless and cast iron applications. Second, machinability varies widely inside a single group. Free-machining 12L14 steel and 4340 at 350 HB are both “ISO P,” but they cannot run anywhere near the same cutting speed.
Carbide Grade Selection: Substrate and Coating Logic
Before looking at parameters, it helps to understand why grade recommendations differ so much between applications. A carbide grade is a combination of a tungsten-carbide substrate (its cobalt content and grain size control toughness versus wear resistance) and a coating system that controls heat and abrasion resistance.
CVD Versus PVD Coatings
- CVD (chemical vapor deposition) coatings such as thick multilayer TiCN plus Al2O3 offer outstanding thermal insulation and are the first choice for steel and cast iron turning at high speeds. The trade-off is a slightly dulled edge (the coating is applied at high temperature) and lower edge strength, which makes them risky on stainless steel and superalloys.
- PVD (physical vapor deposition) coatings such as TiAlN and AlTiN are applied at lower temperatures, leaving a sharp edge with compressive residual stress. This makes them the standard for stainless steel, titanium and hardened steels, where edge strength and resistance to built-up edge matter more than maximum thermal insulation.
- Uncoated fine-grain carbide with polished rake faces dominates aluminum and non-ferrous machining, where coatings provide little benefit and can promote built-up edge.
Typical Grade Classes by Application
| Application Class | Coating System | Representative Grades | Characteristics |
|---|---|---|---|
| Steel, P15–P35 | CVD multilayer TiCN/Al2O3, MT-CVD | Sandvik GC4325, Tungaloy AH3225, Mitsubishi MP6120, Seco TP2501, Sumitomo AC8025P | Balanced tough/abrasive; thick Al2O3 layer for crater resistance |
| Stainless, M10–M30 | PVD TiAlN/AlTiN, fine grain | Sandvik GC2220, Tungaloy AH725, Iscar IC908 | Sharp edge, anti-adhesion, resists built-up edge |
| Cast iron, K10–K30 | CVD multilayer with Al2O3 | Many M-class grades (e.g. AH725) are also K-rated; dedicated K-grades vary by brand | Abrasion resistance for grey iron, toughness for ductile |
| Titanium/superalloys, S | PVD, fine-grain substrate | Sandvik GC1105 and comparable PVD grades | Sharp, smooth edges resist notch wear and adhesion |
| Aluminum, N | Uncoated, diamond-polished | Sandvik H13A/H10F class uncoated grades | Polished rake prevents BUE; sharp geometry for shearing |
| Hardened steel, H | CBN inserts, or PVD carbide below ~55 HRC | Brand-specific CBN classes | Hot hardness; negative geometries with chamfered edges |
Note: grade naming and range coverage differ between manufacturers and change with each catalogue revision. Always confirm the current range designation from the manufacturer’s catalogue or a distributor such as hooguu.com before committing to a grade for production.
Turning Starting Values by Material Group
The following table consolidates realistic first-test values for coated carbide turning inserts (CNMG/DNMG/WNMG style, negative geometry for roughing and semi-finishing). Values assume rigid machines, correct insert geometry for the operation, and standard tool overhang.
| Workpiece Material | Cutting Speed Vc (m/min) | Feed fn (mm/rev) | Depth of Cut ap (mm) | Notes |
|---|---|---|---|---|
| Low-carbon steel (1018, 1020) | 250–400 | 0.25–0.45 | 1–4 | Tends to BUE at low Vc; keep speed up |
| Medium-carbon / alloy steel (1045, 4140, ~250 HB) | 180–320 | 0.20–0.35 | 1–3.5 | CVD grades shine here at the upper range |
| Tool steel, annealed | 120–220 | 0.15–0.30 | 1–3 | Reduce Vc at higher alloy content |
| Austenitic stainless 304/316 | 140–220 | 0.15–0.30 | 1–3 | Keep feed constant; never dwell or rub |
| Duplex stainless 2205 | 120–180 | 0.15–0.25 | 1–2.5 | Higher cutting forces; rigid setup required |
| Grey cast iron GG25 | 250–400 | 0.20–0.45 | 1–5 | Abrasion dominates; check flank wear often |
| Ductile iron GGG50 | 160–260 | 0.20–0.35 | 1–3.5 | Tougher chips than grey iron; more heat |
| Aluminum 6061-T6 / 7075-T6 | 400–1000 | 0.10–0.40 | 1–6 | Uncoated polished grades; unlimited by machine limits |
| Titanium Ti-6Al-4V | 35–70 | 0.10–0.25 | 0.5–2.5 | Flood coolant or high-pressure; avoid hot spots |
| Inconel 718 (aged) | 30–55 | 0.10–0.20 | 0.5–2 | Notch wear is life-limiting; vary ap between passes |
| Hardened steel 48–55 HRC (carbide) | 60–110 | 0.08–0.15 | 0.1–0.5 | PVD grades, strong edge preparation |
| Hardened steel 55–62 HRC (CBN) | 120–200 | 0.08–0.20 | 0.1–0.3 | Hard-turning replaces grinding in many cases |
Reading the Turning Table Correctly
The ranges are not random — the low end suits interrupted cuts, poor rigidity, or higher hardness, while the high end suits continuous cuts on stable machines with fresh edges. A useful habit for roughing steel: pick Vc from the middle of the range, run the highest feed that chip control allows, and let the depth of cut follow the stock. Feed has a much smaller effect on tool temperature than speed, so productivity gains come cheapest from feed increases.
For finishing, the logic inverts. Reduce ap to 0.2–0.8 mm and fn to 0.05–0.15 mm/rev depending on the nose radius (a common rule is fn ≈ 40–60% of the nose radius), then raise Vc 10–30% above the roughing value. Wiper-insert geometries permit roughly double the finishing feed at the same surface roughness, which is worth considering on long turning passes.
Milling Starting Values: Vc and Feed per Tooth
Milling data is expressed as feed per tooth (fz) rather than feed per revolution. The table below applies to solid carbide end mills and indexable milling cutters in the 10–20 mm diameter range with appropriate geometry.
| Material | Vc (m/min) | fz (mm/tooth) | Typical ap | Notes |
|---|---|---|---|---|
| Structural / alloy steel | 150–280 | 0.08–0.20 | Up to 1×Dc profiling; 0.5–2 mm shoulder | Reduce ae for higher Vc |
| Stainless 304/316 | 120–200 | 0.07–0.16 | 0.5–1.5×Dc profiling | Sharp PVD edges; avoid dwell in the cut |
| Grey cast iron | 200–350 | 0.10–0.25 | 1–4 mm | Dry machining common; dust extraction |
| Aluminum 6061/7075 | 500–1500+ | 0.08–0.30 | Unlimited by tool heat in practice | Limited by spindle speed and chip evacuation |
| Titanium Ti-6Al-4V | 40–80 | 0.06–0.12 | Up to 1×Dc with low radial engagement | High-pressure coolant strongly recommended |
| Hardened steel ~50 HRC | 80–150 | 0.04–0.10 | 0.1–0.5 mm finishing | Light radial engagement, consistent chip load |
High-Efficiency Milling and Chip Thinning
Modern slotting and roughing strategies intentionally take very shallow radial depths (ae = 5–10% of cutter diameter) while using the full flute length axially. This spreads heat into the chip instead of the tool and allows dramatically higher material removal rates — but it changes effective feed. When the radial engagement falls below half the cutter diameter, each tooth takes a thinner chip than the programmed feed suggests, and the feed must be compensated upward. The radial chip-thinning factor is:
RCTF = Dc / (2 × √(ae × (Dc − ae)))
As an example, a 12 mm end mill with ae = 1.2 mm (10% of Dc) produces an RCTF of about 2.18 — programmed feed per tooth must roughly double to maintain the intended chip thickness. Manufacturers’ feeds-and-speeds calculators apply this correction automatically; manual programmers should at minimum know it exists, because running a heavily thinned chip at nominal feed causes rubbing, work hardening and rapid edge breakdown in stainless and titanium.
Drilling Starting Values for Solid Carbide Drills
The values below suit modern solid carbide drills with internal coolant in the 10–12 mm diameter range. Scale feed with diameter: small drills need proportionally lower feed to protect the core.
| Material | Vc (m/min) | Feed fn (mm/rev) | Notes |
|---|---|---|---|
| Steel, P | 80–120 | 0.20–0.30 | Self-centering point geometries; no pilot needed |
| Stainless, M | 60–100 | 0.15–0.25 | Constant feed essential; retract only on withdrawal |
| Grey iron, K | 90–140 | 0.25–0.35 | Abrasive; monitor corner wear |
| Aluminum, N | 150–300 | 0.15–0.30 | Polished flutes; watch chip packing in deep holes |
| Titanium, S | 30–55 | 0.08–0.15 | Internal coolant mandatory beyond 3×D |
Peck drilling with small retracts is an HSS-era habit that shortens carbide drill life through edge chipping at every re-entry. Modern carbide drills prefer one continuous plunge with through-coolant, using a pilot only when the drill geometry requires it.
How to Adjust Starting Values for Real Conditions
Catalogue values assume catalogue conditions. Apply these corrections:
- Interrupted cuts: reduce Vc by 10–20% and favor a tougher (lower hardness, higher cobalt) grade over the most wear-resistant option.
- Poor rigidity or overhang beyond 4×D: reduce both Vc and feed by 10–20%; climb milling and smaller nose radii help deflection-limited setups.
- Workpiece hardness increases: every 25 HB increase roughly calls for a 5–10% Vc reduction in the P group.
- Continuous finishing passes: raise Vc 10–30% and shift to a sharper PVD or wiper geometry.
- Coolant strategy: run dry or with consistent flood on CVD steel grades; never intermittent coolant, which causes thermal cracking. Stainless, titanium and superalloys benefit strongly from high-pressure through-tool coolant.
- Machining thin-walled or clamped-short parts: prioritize feed reduction over speed reduction when chatter appears — but if chatter persists, a 5–10% Vc reduction can move the system out of resonance.
Troubleshooting Wear Modes and Parameter Corrections
Tool wear is diagnostic data. The wear pattern on a used edge tells you exactly which parameter to change.
| Wear Mode | What It Looks Like | Primary Cause | Correction |
|---|---|---|---|
| Flank wear (rapid) | Uniform wear band on clearance face growing fast | Vc too high, or grade too soft for the material | Reduce Vc 10–15%; move to a more wear-resistant grade |
| Crater wear | Hollow worn into the rake face | Excess temperature at the chip contact zone | Reduce Vc; select thicker Al2O3 CVD grades |
| Built-up edge | Welded workpiece material on the edge; poor finish | Vc too low; chemically adherent materials (stainless, aluminum) | Raise Vc; use sharper, smoother PVD or polished uncoated edges |
| Edge chipping | Small fractures along the cutting edge | Feed too high for the edge prep; interrupted cuts; instability | Reduce fn; tougher grade; improve clamping and rigidity |
| Thermal cracking | Combs of cracks perpendicular to the edge | Intermittent coolant cycling edge temperature | Run fully dry or fully flooded — never in between |
| Notch wear | Groove at the depth-of-cut line | Work-hardened surface layer (stainless, superalloys) | Increase ap past the hardened layer; vary ap between passes; higher lead angle |
| Plastic deformation | Edge visibly deformed or bulged | Operating temperature above grade limit | Reduce Vc and/or feed; move to a hotter grade class |
Key Takeaways
- Start in the middle of the published Vc range, then optimize with feed first — feed increases are cheaper in tool temperature than speed increases.
- Match coating class to material group: CVD multilayer for steel and cast iron, PVD for stainless and superalloys, uncoated polished for aluminum.
- Respect the chip-thinning effect in high-efficiency milling; nominal feed at low radial engagement will rub instead of cut.
- Read worn edges as feedback: flank and crater wear mean slow down, built-up edge means speed up, chipping means reduce feed or improve rigidity.
- Always cross-check consolidated values against the specific grade’s current manufacturer data before locking production parameters.
Consistent parameter discipline — recording what was run, how many parts each edge produced, and which wear mode ended its life — converts these starting values into a proven in-house database faster than any catalogue can. That data, more than any individual grade choice, is what separates high-performance shops from average ones.
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