CNMG 120408 vs 120412 vs 120416 vs 190616: Insert Size Progression & Selection Guide
4-size geometric matrix · 8-brand grade scaling · workpiece-to-size mapping · DCLNR holder family · Vc/ap/feed trade-offs · migration cheat sheet
1. ISO Code Decoding: Pos 4 and Pos 5 Tell You the Size
CNMG 120408 / 120412 / 120416 / 190616 all decode to the same shape letter family (CNMG = negative rake, 80° diamond, center hole, hole + chipbreaker both faces). The only differences across the four are in positions 4 and 5 of the ISO 1832 code:
Practical reading guide: CNMG 1204xx = the three "12 04" sizes (08, 12, 16 nose radii share the same 12.7 mm IC and 4.76 mm body thickness — only the corner radius differs). CNMG 190616 is the larger step (19.05 mm IC, 6.35 mm thick, 1.6 mm nose). For the full ISO 1832 letter-by-letter decoder see our carbide inserts by ISO code hub.
2. The Geometric Trade-off Matrix — Why Size Matters
Larger CNMG size = bigger cross-section = stronger cutting edge + higher ap + heavier feed allowed, but with trade-offs in minimum workpiece diameter and required holder rigidity:
| Dimension | CNMG 120408 | CNMG 120412 | CNMG 120416 | CNMG 190616 | Implication |
|---|---|---|---|---|---|
| Inscribed circle (IC) | 12.7 mm | 12.7 mm | 12.7 mm | 19.05 mm | 190616 has 50% larger IC → strongest corner |
| Thickness | 4.76 mm | 4.76 mm | 4.76 mm | 6.35 mm | 190616 holds 33% more ap before deflection |
| Nose radius | 0.8 mm | 1.2 mm | 1.6 mm | 1.6 mm | Larger nose = better Ra + stronger corner + higher feed |
| Maximum ap (roughing) | 1.5-6 mm | 2-7 mm | 2.5-8 mm | 4-12 mm | Step up = +50% ap per size |
| Maximum feed f | 0.10-0.40 mm/rev | 0.15-0.50 mm/rev | 0.20-0.55 mm/rev | 0.30-0.70 mm/rev | Bigger size = +25% feed per step |
| Min workpiece Ø | ~20 mm | ~22 mm | ~24 mm | ~35 mm | Bigger nose r needs clearance |
| Standard holder shank | 20 or 25 mm | 25 mm | 25 mm | 32 mm | Heavier cuts need stiffer shank |
| Min holder shank (DCLNR) | 2020 K12 | 2525 M12 | 2525 M12 | 3232 P19 | Below this → chatter / poor finish |
| $/corner (avg 8 brands) | ~$4.85 | ~$5.10 | ~$5.35 | ~$7.50 | Larger size costs more per corner |
| Tool life factor (vs 120408) | 1.0× | 1.3× | 1.6× | 2.5× | Bigger edge = more material before failure |
Practical takeaway: Sizing up increases cutting capacity (ap, f, edge life) but adds cost per corner and minimum workpiece constraint. For 80% of shaft turning on 20-80 mm Ø, CNMG 120408 is the safe default. Step up only when the job clearly demands the larger envelope.
3. Workpiece Diameter to Recommended CNMG Size
The single biggest factor in size selection is workpiece diameter. Match the size to the workpiece first, then refine by ap and feed requirements:
| Workpiece Ø | Recommended Size | Alternative Sizes | Why This Size |
|---|---|---|---|
| 15-30 mm (small shafts, slender) | CNMG 120408 | CNMG 120404 (finishing only) | Min 0.8 mm nose clears small Ø; small ap fits thin walls |
| 30-50 mm (general small turning) | CNMG 120408 | CNMG 120412 (heavier ap) | Universal default; 80% of small-batch turning |
| 50-80 mm (mid-range shafts) | CNMG 120412 | CNMG 120408 (lighter) or 120416 (heavier) | Mid nose radius balances feed and surface finish |
| 80-150 mm (large shafts, hubs) | CNMG 120416 | CNMG 120412 (lower feed job) | Bigger nose + thicker edge takes heavy ap without chipping |
| 150-300 mm (very large parts) | CNMG 190616 | CNMG 120416 (limited ap 6 mm max) | Step up to 19 mm IC for ap above 8 mm and rigidity |
| Above 300 mm (large hubs, rolls) | CNMG 190616 | CNMG 250724 (rare, special order) | Industry-standard largest size for general heavy turning |
| Finishing pass on any of above | Drop to next-smaller nose radius | e.g. 120416 → 120404 for final Ra <0.4 µm | Larger nose gives surface finish; smaller nose gives better Ra |
Heuristic: Pick size by Ø first, then ap. If ap on the job stays below 5 mm on shafts below 80 mm, CNMG 120408 always works. If the spec sheet calls for ap above 6 mm on shafts above 100 mm, skip a size and go to CNMG 120416 or 190616 directly.
4. 8-Brand Grade Matrix Scaling Across 4 Sizes
For each CNMG size, all 8 major brands sell matching grades. PVD grades target stainless 304/316; CVD grades target carbon/alloy steel. Here is the cross-reference matrix with Vc bands by size:
4A. Stainless 304/316 PVD Grades — Vc by Size
| Brand | Grade | CNMG 120408 | CNMG 120412 | CNMG 120416 | CNMG 190616 | $/corner 120416 |
|---|---|---|---|---|---|---|
| Mitsubishi | VP15TF | 150-180 m/min | 140-170 m/min | 130-160 m/min | 110-140 m/min | $5.05 |
| Sandvik | GC2025 | 140-180 m/min | 130-170 m/min | 120-160 m/min | 100-140 m/min | $5.20 |
| Kennametal | KC7315 | 140-180 m/min | 130-170 m/min | 120-160 m/min | 100-140 m/min | $4.90 |
| Iscar | IC8150 | 130-170 m/min | 120-160 m/min | 110-150 m/min | 90-130 m/min | $4.75 |
| Walter | WPP05 | 100-150 m/min | 95-140 m/min | 90-130 m/min | 70-110 m/min | $6.10 |
| Korloy | NC3220 | 140-180 m/min | 130-170 m/min | 120-160 m/min | 100-140 m/min | $3.95 |
| Sumitomo | AC6020M | 130-170 m/min | 120-160 m/min | 110-150 m/min | 90-130 m/min | $5.20 |
| Tungaloy | T9115 | 120-160 m/min | 110-150 m/min | 100-140 m/min | 85-120 m/min | $5.55 |
How to read this table: As size increases (120408 → 190616), recommended Vc drops by 25-30% across all grades. This is because larger contact area generates more heat per unit time. Maintain surface speed in m/min, not RPM.
4B. Carbon/Alloy Steel CVD Grades — Vc by Size
| Brand | Grade | CNMG 120408 | CNMG 120412 | CNMG 120416 | CNMG 190616 | $/corner 120416 |
|---|---|---|---|---|---|---|
| Mitsubishi | US7020 | 200-260 m/min | 190-250 m/min | 180-240 m/min | 160-220 m/min | $5.30 |
| Sandvik | GC4325 | 200-260 m/min | 190-250 m/min | 180-240 m/min | 160-220 m/min | $5.45 |
| Kennametal | KC9325 | 210-270 m/min | 200-260 m/min | 190-250 m/min | 170-230 m/min | $5.10 |
| Iscar | IC8250 | 180-240 m/min | 170-230 m/min | 160-220 m/min | 140-200 m/min | $4.85 |
| Walter | WSM35 | 180-240 m/min | 170-230 m/min | 160-220 m/min | 140-200 m/min | $6.30 |
| Korloy | NC3120 | 190-250 m/min | 180-240 m/min | 170-230 m/min | 150-210 m/min | $3.80 |
| Sumitomo | AC8025P | 200-260 m/min | 190-250 m/min | 180-240 m/min | 160-220 m/min | $5.30 |
| Tungaloy | T9125 | 190-250 m/min | 180-240 m/min | 170-230 m/min | 150-210 m/min | $5.60 |
For complete grade equivalency across steel + stainless + cast iron, see our grade cross-reference hub. For material selection across P/M/K ISO groups, see the carbide inserts by material pillar.
5. Tool Holder Family and Shank Sizing
All 4 CNMG sizes fit the same 95° approach angle holder family (DCLNR / DCLNL / DCLCR). The difference is shank cross-section — larger insert needs stiffer shank to support heavier ap:
| Holder Code | Shank | Insert Capacity | Max ap Recommended | Common Use |
|---|---|---|---|---|
| DCLNR/L 1616 H12 | 16 × 16 mm | CNMG 120404 / 120408 only | 3 mm | Small lathe, Swiss-style, finishing |
| DCLNR/L 2020 K12 | 20 × 20 mm | CNMG 120408 / 120412 | 5 mm | Mid-range general turning |
| DCLNR/L 2525 M12 | 25 × 25 mm | CNMG 120408 / 120412 / 120416 | 7 mm | Universal turning, 70% of heavy roughing |
| DCLNR/L 3232 P19 | 32 × 32 mm | CNMG 190616 | 12 mm | Heavy-duty shaft turning, large parts |
| DCLCR/L 2525 M12 | 25 × 25 mm (top clamp) | CNMG 120408 / 120412 / 120416 | 7 mm | Easier insert indexing, light cuts |
| MCBNR/L 2525 M12 | 25 × 25 mm (95°-75°) | CNMG 120408 / 120412 / 120416 | 5 mm | Turning toward chuck (reverse spindle) |
Cantilever rule: For chatter-free performance, the overhang (distance from holder shank to insert tip) should not exceed 3-4× the shank cross-section. A 25 × 25 mm shank with 100 mm overhang is acceptable; 150 mm is borderline. For the full holder family including boring bars and coolant-through options, see our tool holder guide.
6. Cutting Parameters by Size — Vc / f / ap at a Glance
| Size | Stainless 304 PVD Vc | Steel P CVD Vc | Feed f (mm/rev) | ap Roughing (mm) | ap Finishing (mm) |
|---|---|---|---|---|---|
| CNMG 120408 | 130-180 m/min | 200-260 m/min | 0.10-0.40 | 1.5-5.0 | 0.3-1.5 |
| CNMG 120412 | 120-170 m/min | 190-250 m/min | 0.15-0.50 | 2.5-6.5 | 0.5-2.0 |
| CNMG 120416 | 110-160 m/min | 180-240 m/min | 0.20-0.55 | 3.0-8.0 | 0.5-2.5 |
| CNMG 190616 | 90-140 m/min | 160-220 m/min | 0.30-0.70 | 5.0-12.0 | 1.0-3.0 |
Trend: As size increases, Vc drops 10-15% per step, feed rises 25% per step, and ap potential grows 50% per step. For Vc/f/ap formulas and material-specific calculator, see our speeds & feeds hub.
7. Mitsubishi VP15TF vs Sandvik GC2025 vs Korloy NC3220 — Cross-Size Comparison
The three most popular PVD stainless grades offer different price/performance trade-offs as you scale through the 4 sizes:
| Size | VP15TF Vc | VP15TF Price | GC2025 Vc | GC2025 Price | NC3220 Vc | NC3220 Price |
|---|---|---|---|---|---|---|
| CNMG 120408-PM | 150-180 m/min | $4.65 | 140-180 m/min | $4.85 | 140-180 m/min | $3.50 |
| CNMG 120412-PM | 140-170 m/min | $4.85 | 130-170 m/min | $5.05 | 130-170 m/min | $3.75 |
| CNMG 120416-PM | 130-160 m/min | $5.05 | 120-160 m/min | $5.20 | 120-160 m/min | $3.95 |
| CNMG 190616-PM | 110-140 m/min | $7.10 | 100-140 m/min | $7.25 | 100-140 m/min | $5.50 |
Practical takeaway: Korloy NC3220 is consistently 25% cheaper than Mitsubishi VP15TF and Sandvik GC2025 across all 4 sizes. Mitsubishi VP15TF offers the highest Vc at every size (5-10% faster than Sandvik). For shops running high-volume stainless 304 turning, the cost-per-corner savings of NC3220 add up fast. For deeper grade equivalency see our VP15TF equivalent guide.
8. When to Size Up — A Practical Decision Tree
Use this sequence to pick the right CNMG size without over- or under-sizing:
- Step 1 — workpiece Ø: Match the size per the table in section 3. If Ø <80 mm, default to CNMG 120408. If Ø 80-150 mm, default to CNMG 120416. If Ø >150 mm, default to CNMG 190616.
- Step 2 — depth of cut: If ap is consistently above 6 mm on shafts 50-80 mm, skip to CNMG 120416. If ap is consistently below 2 mm and Ø is small, drop to CNMG 120404 for better finishing.
- Step 3 — feed requirement: If the cycle-time study calls for f >0.5 mm/rev, pick CNMG 120416 or above. If f <0.2 mm/rev on a finishing pass, even CNMG 120408 works fine.
- Step 4 — surface finish target: For Ra target <0.8 µm on 304 stainless, step down to the next-smaller nose radius (e.g. CNMG 120404 from 120408, or CNMG 120408 from 120416) for the final pass.
- Step 5 — holder rigidity: Make sure your DCLNR holder shank matches. CNMG 190616 on a 25 × 25 mm shank will chatter; you need a 32 × 32 mm shank for stability.
Final sanity check: When in doubt, pick the smaller size. Modern CNMG 120408-PM grades are so efficient that oversizing wastes cost per corner. The rare exceptions are shafts above 150 mm where CNMG 190616 is the only practical choice.
9. Migration Cheat Sheet — Moving Up or Down the Size Family
When existing tooling parameters need to step to a larger or smaller CNMG size, here's how parameters translate:
| If You Run | Switch To | Holder Change | Vc Change | Feed Change | ap Change |
|---|---|---|---|---|---|
| CNMG 120408 at Vc 170, f 0.30, ap 4 mm, 304 stainless | CNMG 120412 | None (same DCLNR 2525 M12) | -5% | +15% | +30% |
| CNMG 120412 at Vc 160, f 0.40, ap 6 mm, 304 stainless | CNMG 120416 | None (same DCLNR 2525 M12) | -5% | +10% | +20% |
| CNMG 120416 at Vc 145, f 0.45, ap 7 mm, 304 stainless | CNMG 190616 | DCLNR 2525 → DCLNR 3232 P19 | -15% | +25% | +50% |
| CNMG 120416 at Vc 145, f 0.30, ap 7 mm, 304 finishing Ra 1.6 µm | CNMG 120408 (final 1 pass finishing) | None (same holder, drop nose r) | +10% | -30% | -50% |
| CNMG 120408 at Vc 170, f 0.40, ap 5 mm, mild steel | CNMG 120412 (heavier cycle) | None | -5% | +15% | +30% |
| CNMG 190616 at Vc 130, f 0.6, ap 10 mm, large hub finishing | CNMG 250724 (special order) | DCLNR 3232 → special 40×40 shank | -10% | +15% | +30% |
For deeper shaping comparisons (CNMG vs DNMG vs SNMG geometry) see our DNMG 150608-PM vs CNMG 120408-PM guide, and for the single-size deep dive on CNMG 120408 see the CNMG 120408-PM 8-brand grade guide.
10. Frequently Asked Questions
Should I size up from CNMG 120408 to CNMG 120416 for finishing?
No. Sizing up is for roughing (more ap and feed). For finishing, the rule is the opposite: drop to the next-smaller nose radius to get better surface finish. If you're using CNMG 120416 for roughing at ap 7 mm and want Ra 0.8 µm on a 304 stainless shaft, do the roughing pass with 120416 then change to CNMG 120408 for one finishing pass at ap 1 mm and f 0.10 mm/rev. This gives Ra 0.6-0.8 µm with much longer tool life than trying to finish with 120416 alone.
What's the actual difference between CNMG 120412 and CNMG 120416?
Both share the same 12.7 mm IC and 4.76 mm body thickness — the difference is in nose radius only (1.2 mm vs 1.6 mm). The 0.4 mm extra nose radius gives 120416 three benefits: (1) about 25% higher allowed feed before edge chipping, (2) about 15% more ap allowance (ap 8 mm vs 7 mm), and (3) about 30% longer tool life under the same parameters. Trade-off: 120416 cannot fit workpieces below 24 mm diameter (vs 22 mm for 120412), and gives slightly rougher surface finish at the same feed (because larger nose radius = larger cusp height per revolution).
When do I need CNMG 190616 instead of CNMG 120416?
CNMG 190616 (19.05 mm IC vs 12.7 mm) becomes necessary when: (1) workpiece diameter above 150 mm and ap above 8 mm on a single pass, (2) high-feed turning above 0.6 mm/rev requires the bigger edge cross-section, or (3) heavy-roughing cast iron where the larger 19 mm IC chipbreaker geometry is more efficient. For 80% of heavy turning jobs, CNMG 120416 on a 25 × 25 mm DCLNR 2525 M12 holder still works. Step up to 190616 only when the spec sheet demands ap 8-12 mm or larger workpiece rigidity requirements.
Can I use the same DCLNR 2525 M12 holder for CNMG 120408, 120412, and 120416?
Yes — DCLNR/L 2525 M12 is the universal holder for all three sizes in the CNMG 1204xx family (12.7 mm IC). The "M12" designation means it accepts any CNMG/CNMA/CNMM insert with IC = 12 mm. You only need to swap the shim and clamping when going from CNMG 1204xx to CNMG 190616 (which needs the bigger DCLNR 3232 P19 holder). The shank cross-section (25 × 25 mm) is sufficient for ap up to 7 mm, which covers all CNMG 1204xx sizes.
What nose radius is best for finishing Ra 0.4 µm on 304 stainless?
For Ra 0.4 µm on 304 stainless with CNMG-PM, use CNMG 120404-PM (nose r 0.4 mm) at parameters Vc 160-180 m/min, f 0.05-0.08 mm/rev, ap 0.3-0.5 mm. The smaller 0.4 mm nose radius (vs 0.8 mm on 120408) reduces cusp height per revolution by ~50%, directly translating to lower Ra. Expected tool life is ~40% shorter than 120408 due to smaller contact area, so use this for the final finishing pass only and run roughing with CNMG 120408-PM. For Ra 0.6-0.8 µm (looser finishing target), CNMG 120408-PM works without the second finishing pass.
Does bigger CNMG size give longer tool life on the same job?
Yes — and the gain is roughly proportional to the cross-section increase. CNMG 120408 (~60 mm² insert cross-section) typically gives 18-22 minutes tool life at standard parameters on 304 stainless. CNMG 120416 (~80 mm²) gives 28-32 minutes under the same Vc and feed. CNMG 190616 (~120 mm²) gives 40-50 minutes. Bigger size = more wear-resistant material per cutting edge = longer interval before edge chipping. Trade-off: lower Vc is recommended, which can offset cycle-time gains. Net productivity (parts per shift) usually peaks at CNMG 120416 for typical roughing operations.
11. Related Pillar Guides
- Carbide inserts by material — stainless (M), steel (P), cast iron (K) selection.
- Carbide inserts by operation — turning, milling, drilling geometry families.
- Carbide inserts by ISO code — letter-by-letter ISO 1832 decoder.
- Grade cross-reference hub — 8-brand grade matrix for steel + stainless.
- Speeds & feeds calculator — Vc / f / ap formulas by material.
- Tool holder guide — DCLNR/DDJNR family selection.