sandviks CNMG 120408-PF 4225 Carbide Turning Insert CNMG 432 Sandviks CVD Coated 80 Degree Rhombic Finishing Insert for Steel

The CNMG 120408-PF 4225 is a double-sided, negative-rake turning insert from sandviks Coromant's T-Max® P range. It uses the 12.7 mm (1/2") 80° rhombic body with a 0.8 mm corner radius — the most widely used radius in general turning — paired with the PF finishing chipbreaker.

R0.8 is the practical default for a reason: it is strong enough to survive semi-finishing feeds and light interruptions, yet fine enough to hold surface finish and tolerances on most medium-sized steel parts. Where a R0.4 edge would chip and a R1.2 edge would smear on light cuts, R0.8 sits in the useful middle.

The insert is produced in GC4225, a CVD-coated carbide grade on a gradient substrate. The MT-Ti(C,N) / Al₂O₃ / TiN coating resists crater and flank wear at high cutting temperature, while the cobalt-enriched surface zone protects the edge line under light interruption.

With 12.7 mm inscribed circle and 4.76 mm thickness, it is the metric twin of the ANSI CNMG 432 — the most frequently searched inch designation for this insert size.

• R0.8 corner radius — the general-purpose choice: better edge strength and higher feed capacity than R0.4, better chip control on light cuts than R1.2.
• 80° rhombic, negative geometry — four usable cutting edges, two per face; economical cost per edge.
• PF finishing chipbreaker — low depth of cut and low feed, short controllable chips, good surface quality on finishing passes.
• GC4225 CVD-coated grade — thick multilayer coating on a tough gradient substrate; stable in continuous cutting and light interruption.
• Cylindrical centre hole — standard lever or screw clamping, fits every 12-size CNMG seat.

Dimensional values follow ISO 1832 / ISO 13399 for the CNMG 120408 size. Tolerances: IC ±0.08 mm, thickness ±0.13 mm.

CNMG 12 04 08 -PF 4225

ANSI conversion: CNMG 120408 = CNMG 432. The last digit pair is the radius in 1/64": 08 mm ≈ 2/64" → code 2. A 12 radius (1.2 mm) would be code 3, i.e. CNMG 433 — a different SKU.

If the workpiece is slender, thin-walled or the setup is less rigid, R0.8 is the safer choice. If the operation pushes feed and the edge keeps chipping, move up to R1.2.

PF is sandviks's finishing geometry, intended for low depth of cut and low feed rates where chip control and surface finish matter more than metal removal rate.

Choose PF when:

• depth of cut is shallow (finishing and semi-finishing);
• surface finish and dimensional accuracy dominate;
• cutting forces should stay low (weak setup, slender part).

Move to a medium or roughing geometry (PM / PR or equivalent) when:

• depth of cut regularly exceeds about 1 mm;
• the cut is heavily interrupted or includes cast skin;
• high metal removal rate is the goal.

GC4225 is a CVD-coated carbide grade for finishing to roughing of steel and steel castings. A gradient substrate combines a hard surface with a tough core; the thick multilayer coating resists crater and flank wear at elevated temperature.

Typical behaviour:

• stable in continuous turning and light interrupted cuts;
• broad working range, tolerant of material batch variation;
• suitable for wet and dry machining.

Grade generation note: GC4225 is an earlier P25 generation. sandviks's current programme positions GC4425 at P25, following GC4225 → GC4325 → GC4425. GC4325 and GC4425 are the functional successors if GC4225 supply is limited.

• Semi-finishing and finishing of shafts, sleeves, flanges, hubs and general engineering parts
• Profile and copy turning where the 80° rhombic reaches shoulders and contours
• Facing, chamfering and light interrupted cuts on CNC lathes
• Steel and steel castings (P group); limited use in stainless steel and cast iron

Not recommended for:

• heavy roughing at deep depth of cut — use a roughing geometry and tougher grade;
• severe scale or casting skin — edge chipping risk;
• aluminium finishing — use uncoated polished inserts.

CNMG 120408 uses the 12-size insert seat. Typical families (examples, not exhaustive):

• PCLNR / PCLNL 2525M12 — 95° approach, right / left hand
• MCLNR / MCLNL 2525M12 — 95° approach, neutral clamping style
• DCLNR / DCLNL 2525M12 — 95° approach, heavy-duty body

Match the seat code (12) and hand (R/L) to the operation; the same insert covers external turning, facing and boring with the right holder.

• Standard pack: 10 pieces per box (confirm against the actual packing list before publishing)
• Order by full designation: CNMG 120408-PF 4225
• Check grade availability first — GC4225 is an earlier-generation grade and stock varies by region

Is CNMG 120408 the same as CNMG 432? Yes. 120408 is the ISO metric designation, CNMG 432 the ANSI inch designation — same insert, R0.8 corner radius.

Does CNMG 432 fit the same holder as CNMG 433? Yes. Both are 12-size inserts with identical IC and thickness, so the holder is the same. Only the corner radius differs, which changes the cutting behaviour, not the mounting.

How many cutting edges? Four — it is double-sided, two edges per face.

Can it rough? Light roughing only. PF is a finishing geometry; sustained deep cuts need a tougher chipbreaker.

What replaces GC4225? GC4325 first, then GC4425. Re-optimise cutting data rather than copying the old values.