Grooving & Parting Tool Width Selection
Parting and grooving insert widths by diameter per Sandvik, overhang rigidity rules, and standard groove widths for O-rings, retaining rings and thread reliefs.
Parting / cut-off insert width by part diameter
| Part diameter D (mm) | Insert width CW (mm) | Min. practical width (mm) | Setup note |
|---|---|---|---|
| D ≤ 10 | 1.0 | 1.0 | Slender rods and tubes: the smallest width with the sharpest edge, to minimise cutting force and vibration. |
| 10 < D ≤ 25 | 1.5 | 1.5 | Medium parting; keep the overhang as short as possible. |
| 25 < D ≤ 40 | 2.0 | 2.0 | Rigid set-up; a 2-edge insert is fine. |
| 40 < D ≤ 50 | 2.5 | 2.5 | — |
| 50 < D ≤ 65 | 3.0 | 3.0 | Deep parting: single-edge insert with a stable spring clamp — insert stability is critical at these forces. |
| 65 < D ≤ 100 | — | — | No verified vendor table value; large diameters need a taller blade and stable clamping. Size from the manufacturer catalogue — do not extrapolate. |
| D > 100 | — | — | Sandvik parts diameters up to ≈180 mm with Y-axis CoroCut QD — that is a set-up capability, not a width value. |
How to read this table. Widths are the published Sandvik Coromant table, which ends at Ø65 mm. No vendor width table in our sources covers 65–100 mm or above 100 mm — size those from the tool maker's catalogue; do not extrapolate the ladder.
External, Face and Internal Grooving
Only external grooving has a published width table — the same ladder as parting. Face and internal grooving are set by chip evacuation, groove curvature and overhang, so they are designed per part rather than read off a chart.
| Grooving type | Width guidance | Main difficulty |
|---|---|---|
| External grooving / parting | Standard insert widths 1.0 / 1.5 / 2.0 / 2.5 / 3.0 mm — take the narrowest that carries the groove | Narrower blades cut with less force and waste less material, but they need stable clamping and a short overhang. |
| Face grooving | No universal width table — the tool path follows the groove curvature | Chip evacuation and the groove bending radius decide the tool path; overhang and vibration are the main difficulties. |
| Internal grooving | No published diameter-to-width table | Long overhang, chip evacuation, vibration and tool stability; use solid or damped bars with through coolant. |
Standard Groove Widths by Function
Functional grooves take their width from the mating standard, not from preference: retaining-ring grooves equal the ring thickness, O-ring grooves follow the seal design rules, thread reliefs follow the thread standard. Non-functional grooves should drop onto a standard insert width so no custom tooling is needed. Depth proportions for O-ring grooves are not listed here — read them from the standard (ISO 3601-2 / GB/T 3452.3) for the exact cross-section.
| Groove function | Common groove width | Tolerance & related dimensions | Standard |
|---|---|---|---|
| O-ring seal groove, static | ≈ 1.3–1.9 × cross-section (CS) — CS 1.8 → ≈ 2.3–3.4; CS 2.62 → ≈ 3.4–5.0; CS 3.53 → ≈ 4.6–6.7; CS 5.33 → ≈ 6.9–10.1 (mm) | Static squeeze 15–30%; groove-bottom radius R0.1–0.3 | ISO 3601-2 / GB/T 3452.3 |
| Retaining-ring groove, shaft (DIN 471 type) | Groove width = ring thickness s — shaft Ø30 → s ≈ 1.5; Ø50 → s ≈ 2.0; Ø100 → s ≈ 3.0 (mm) | Shaft Ø30: groove-bottom diameter d3 ≈ 27.5–28.1 mm; width toleranced per the standard table | DIN 471 / GB/T 894.1 |
| Thread-relief / undercut groove | At least the tool cutting width, plus a 0.5–1 mm margin | Free tolerance; dimensioned as width × depth or width × diameter | GB/T 3-1997 |
| Functional / non-standard groove | 2 / 2.5 / 3 / 4 mm — standard insert widths cut it without custom tooling | Designer-defined; check the mating standard if a ring or seal seats in it | Standard insert width ladder (1 / 1.5 / 2 / 2.5 / 3) |
Overhang, Clamping and Cutting Force
The width choice only pays off if the set-up is stiff. These relations come from Sandvik's parting and grooving knowledge base.
| Rule | Numbers | Practical effect |
|---|---|---|
| Shorten the overhang before upgrading anything else | Deflection grows with the cube of overhang: 100 → 80 mm overhang ≈ 0.51× the deflection | A shorter overhang beats any insert upgrade at the same width. |
| Y-axis parting raises stiffness | Y-axis parting: more than 6× the bending stiffness at a 60 mm blade overhang | Less vibration and a higher allowable feed. |
| Feed threshold on overhang | Overhang under 1.5 × blade height (H): recommended feed; beyond it, drop to the low end of the feed band | Measure the real overhang before choosing the feed. |
| Clamp the bar long enough | Bar clamping length ≥ 4 × bar diameter D | Shorter clamping lets slender bars whip and pinch the blade. |
| Narrow blade, lower force | Narrower insert: lower cutting force, less swarf; small widths lower radial force on fragile parts | The trade is setup sensitivity — clamp close and keep the overhang short. |
How to Use These Numbers
- Non-functional groove widths should land on 2 / 2.5 / 3 / 4 mm so a standard insert cuts them in one pass — no custom tooling, no second operation. Functional grooves (seals, retaining rings) take the standard's width instead of an invented value.
- Up to Ø10 mm part with a 1.0 mm blade; 10–25 mm with 1.5 mm. Narrower blades mean less cutting force and less material scrapped, but they punish a loose setup: clamp the bar at ≥ 4 × D and work close to the chuck.
- Keep the blade overhang under 1.5 × blade height. Beyond that, drop the feed to the low end of the recommendation — deflection grows with the cube of overhang, and Y-axis parting buys back more than 6× stiffness at 60 mm overhang.
- Set the blade on centre within ±0.1 mm, especially when cutting through to the axis. Off-centre parting raises burrs and flanges and chips corners.
- Never tweak a retaining-ring groove: for a Ø30 shaft, DIN 471 wants width = ring thickness s ≈ 1.5 mm and groove-bottom diameter d3 ≈ 27.5–28.1 mm. A wider or deeper groove stops the ring from doing its job.
Frequently Asked Questions
What grooving insert width should I use to cut off a Ø25 mm bar?
1.5 mm — Ø25 sits in the 10–25 mm band. The next band up (25–40 mm) takes 2.0 mm.
1.5 mm — Ø25 sits in the 10–25 mm band. The next band up (25–40 mm) takes 2.0 mm.
What groove width for a retaining ring on a Ø30 mm shaft (DIN 471)?
The ring thickness: s ≈ 1.5 mm, with groove-bottom diameter d3 ≈ 27.5–28.1 mm per DIN 471 — not 2.5–3 mm.
The ring thickness: s ≈ 1.5 mm, with groove-bottom diameter d3 ≈ 27.5–28.1 mm per DIN 471 — not 2.5–3 mm.
How wide should an O-ring groove be for a 3.5 mm cross-section O-ring?
Static groove width ≈ 1.3–1.9 × CS, so 4.6–6.7 mm for a 3.5 mm cross-section, per the ISO 3601-2 / GB/T 3452.3 design rules. Take the depth proportions from the standard for the exact cross-section.
Static groove width ≈ 1.3–1.9 × CS, so 4.6–6.7 mm for a 3.5 mm cross-section, per the ISO 3601-2 / GB/T 3452.3 design rules. Take the depth proportions from the standard for the exact cross-section.
Can I cut a Ø40 mm part with a 3 mm grooving insert?
40–50 mm calls for 2.5 mm; 3.0 mm is the 50–65 mm band. It works, but the over-width blade adds cutting force and wastes material on a Ø40 part.
40–50 mm calls for 2.5 mm; 3.0 mm is the 50–65 mm band. It works, but the over-width blade adds cutting force and wastes material on a Ø40 part.
What is the smallest parting width for a thin Ø8 mm rod?
1.0 mm (the ≤10 mm band). On fragile, slender parts use the smallest width with the sharpest edge.
1.0 mm (the ≤10 mm band). On fragile, slender parts use the smallest width with the sharpest edge.
Does a narrower insert reduce cutting force?
Yes — a narrower insert cuts with less force and wastes less material, and small widths also lower radial force on fragile parts. The price is a stiffer, closer setup.
Yes — a narrower insert cuts with less force and wastes less material, and small widths also lower radial force on fragile parts. The price is a stiffer, closer setup.
What is a safe overhang for a parting blade?
Under 1.5 × blade height; beyond that, drop the feed to the low end. Deflection grows with the cube of overhang — at 60 mm overhang, Y-axis parting is more than 6× stiffer.
Under 1.5 × blade height; beyond that, drop the feed to the low end. Deflection grows with the cube of overhang — at 60 mm overhang, Y-axis parting is more than 6× stiffer.
Standards & Sources
- Sandvik Coromant knowledge base — Parting off (insert width by diameter; overhang, clamping and Y-axis stiffness relations)
- Sandvik Coromant knowledge base — Tool set-up, Face grooving and Internal grooving pages
- ISCAR Swiss-Cut / ISO turning selection principles — small widths for small or fragile diameters
- DIN 471 retaining-ring dimension table (secondary database source; confirm against the standard text; Chinese equivalent GB/T 894.1)
- O-ring groove width proportions per ISO 3601-2 / GB/T 3452.3 design rules — example tiers calculated from the ratio, not read from the standard tables
- Thread-relief dimensioning per GB/T 3-1997 (free tolerance; width × depth or width × diameter callout)
Related Pages
- /wiki/reference/relief-undercut-chamfer/ — Sibling quick table: thread undercuts (GB/T 3, DIN 76) and chamfer standards
- /wiki/reference/cutting-parameters/ — Sibling quick table: cutting speeds and feeds for turning and milling
- /wiki/dfm/tolerance-design/ — How to tolerance grooves and fits on the drawing
- /wiki/tolerances/fit-types/ — When a groove needs an individual tolerance instead of a general one