Countersink forming tools
Formed and coined sheet-metal countersinks, their distinction from cutting and dimpling, and geometry-dependent tooling limits.
Tags: tooling, sheet-metal, forming, countersinks
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For an ideal cut countersink with 8.0 mm major diameter and 4.5 mm through hole, a 90° included angle gives 1.75 mm depth. In 2.0 mm flat sheet that leaves 0.25 mm of cylindrical land. At 100°, depth is about 1.47 mm. Using ideal recess depth only as a comparison, the 90° result exceeds Mate's dedicated-tool guideline of 85% of thickness (1.70 mm here). The cone calculation leaves deformation, springback and joint strength unresolved. Mate dedicated-tool depth description.
What the tool produces
TRUMPF 0699335 deforms the sheet into a screw or rivet seat after hole piercing. TRUMPF countersink tool 0699335
A conical seat can be machined, coined or dimpled. Inspect the section and opposite face to distinguish them.
Cutting, coining and dimpling
| Approach | Material action | Important distinction |
|---|---|---|
| Machined countersink | A cutting bit removes material to create a conical recess | Material is removed from the original sheet section |
| Coined countersink | A punch presses material into its final shape | Wilson Tool favors this approach for thicker material and close hole tolerance |
| Formed countersink | A punch bends material to create the recess | Wilson Tool favors this approach for thinner material |
| Dimple for a flush rivet | Matched male/female dies deform the area around a hole into a head seat | The formed shape can nest into a corresponding recess in the adjoining member |
The cutting and dimpling descriptions above follow EAA's aircraft-building explanation; its structural application rules are not adopted here as general sheet-metal limits. The coining/forming distinction follows Wilson Tool's own product terminology. Both Wilson tool types are available in form-down and self-stripping form-up versions. EAA, Flush Riveting Tips; Wilson Tool countersinks
Interpretation: these terms overlap in practice. Formed countersink is a broad description; coining identifies local compression, while dimpling emphasizes the displaced sheet profile. They are not interchangeable assurances of a flat back face, preserved thickness or a particular fastener fit.
Dedicated tooling and manufacturer bounds
Mate describes its dedicated countersink as a tool for one material thickness and one screw size, with a flattening surface around the hole, a blank die and a form depth up to 85% of sheet thickness. That percentage belongs to Mate's described dedicated design, not every countersink process. Mate tooling glossary, Dedicated Countersink
Separately, Mate's special-applications overview lists a typical countersink thickness range of 1.22–6.35 mm, conditional on press tonnage. It says the shoulder style coins the surrounding area to minimize burrs. The upper thickness is an application description, not proof that any installed tool can process every material at that thickness. Mate special-applications overview, Countersink
TRUMPF's upward countersink forming tool 699947 has a listed 0.5–3.0 mm sheet-thickness range and a 90° section drawing. Its catalog describes M2.5–M10 forms and states that each tool is designed for a specific sheet thickness and countersink diameter; machine, material and dimensions are ordering inputs. These limits apply to that cataloged tool, not the whole forming category. TRUMPF punching-tools catalog, p. 86
Check the stated thickness, tool drawing, press capacity and application for each catalog range.
Worked recess geometry
Idealized calculation: let D be the larger seat diameter, d the cylindrical through-hole diameter, α the included cone angle and h the axial conical depth. Ignoring edge radii and any straight land, right-triangle geometry gives:
h = (D − d) / [2 × tan(α / 2)]
For an assumed D = 8.0 mm, d = 4.5 mm and α = 90°, h = (8.0 − 4.5)/2 = 1.75 mm. In a flat 2.0 mm sheet, an ideal cut recess of that depth leaves only 2.0 − 1.75 = 0.25 mm of axial cylindrical land below the cone. This is a geometric remainder, not a strength calculation or an approved minimum land.
At α = 100° with the same diameters, h = 3.5/[2 × tan(50°)] ≈ 1.47 mm. Thus angle changes depth even when the major diameter and hole diameter remain fixed. Neither example assumes an actual screw standard or head tolerance.
For comparison only, 85% of 2.0 mm is 1.70 mm, so the first example's 1.75 mm depth exceeds Mate's stated dedicated-tool proportion. This comparison uses the ideal recess depth as the form-depth measure; it does not predict achievable deformation, springback or a pre-punch diameter. Mate dedicated-tool depth description
A formed recess moves material, so the cut-recess land subtraction cannot describe its final wall thickness or backside envelope. Tool radii, local compression and sheet displacement require a section specific to that form. Finished hole diameter is also not enough to derive the starting hole by cone geometry alone.
Application and coverage limits
Relevant assembly properties include head angle, major seat diameter, final hole diameter, required flushness, backside clearance and the adjoining part's contact surface. Tooling feasibility additionally depends on sheet alloy/condition, thickness, form direction, station geometry and the press's permitted forming load. A successful recess shape alone establishes neither fastener seating strength nor sheet flatness after a complete pattern of hits.
The cited TRUMPF catalog carries identifier 1798794_EN_202204_S and states that prices apply from April 1, 2022; the commercial validity date is not treated as a separate technical revision date. The cited Wilson Tool, Mate, EAA and TRUMPF product pages have no established issue date in this reference. Upload-path and crawl dates are not editions. This article does not supply production settings, pre-punch dimensions, tonnage tables or structural acceptance criteria.