# Joggled flanges

Specifying local flange offsets for overlapping parts, with defined surfaces, runouts, tooling and assembly tolerances.

Reviewed: 2026-11-01

Tags: parts-and-design, features, sheet-metal

Specify the joggle offset, mating thickness and completed flushness as separate dimensions.

The worked overlap has 1.50 ±0.05 mm sheet thickness and 1.50 ±0.10 mm inward offset. The difference ranges from **−0.15 mm recessed to +0.15 mm proud** despite nominally flush faces. This stack excludes coatings, gaps, angular error and waviness.

The FAA airframe handbook describes a joggle as an offset providing clearance for a sheet or another mating part, including intersections of stringers and formers. The material to be cleared governs the required depth. This is useful terminology and forming context; an educational handbook does not approve a particular aircraft modification or establish a universal production dimension. [FAA, Aviation Maintenance Technician Handbook—Airframe, FAA-H-8083-31B, Chapter 4, 2023](https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/FAA-H-8083-31B_Aviation_Maintenance_Technician_Handbook.pdf)

## Define the finished feature

A pair of opposite bends can produce an offset with parallel incoming and outgoing surfaces. A local joggle on an angle or curved flange additionally has to transition back into the unjoggled region. Distinguish the cross-sectional offset from the feature's extent along the flange: a Z-profile through the whole part is not automatically equivalent to a localized clearance pocket in one flange.

| Requirement | Definition to provide |
| --- | --- |
| Offset depth/height | Named reference surfaces, direction and tolerance |
| Transition/runout | Start/end references, length or slope, and radii |
| Joggle extent | Length along the flange and relation to the mating part |
| Final surfaces | Parallelism/profile, flushness and required seating contact |
| Assembly interface | Overlap, gap, fastening/sealing requirements and edge condition |

Do not label all these distances “joggle length.” A drawing should make clear whether length means the transition distance, the overlap region or the entire feature. Likewise, identify inside versus outside radii and the face held fixed during inspection.

Ansys Discovery **2025 R1** defines its Joggle height between the top surface entering the lower bend and the top surface leaving the upper bend. Its bend angle and inside radius apply to both bends; bend allowance or deduction controls flat length. This is a specific CAD definition, not a guarantee that another system's offset field uses the same references. [Ansys, Creating a Joggle, Release 2025 R1](https://ansyshelp.ansys.com/public/Views/Secured/corp/v251/en/discovery/Discovery/user_manual/sheetmetal/t_create_bend_joggle.html)

## Choose the process with the supplier

The FAA describes brake forming for straight/flat regions and forming blocks or dies for curved parts or curved flanges. It also notes that the allowance between bends depends on the material and feature type and should follow the drawing. A local offset in an existing angle can therefore need a different forming plan from a straight strip. Do not transfer a flat-strip allowance to an extrusion without review. [FAA-H-8083-31B, Chapter 4, Joggling](https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/FAA-H-8083-31B_Aviation_Maintenance_Technician_Handbook.pdf)

Dedicated Z tooling can form short, closely spaced offsets that are awkward to produce as two independently supported bends. TRUMPF's **01/2025** bending-tool catalog distinguishes 90°-to-90° coining from air bending with different offsets and angles greater than 90°. Its Z-bending table lists different maximum thicknesses for each method. For example, the Z4 row lists 1 mm for coining and 1.5 mm for air bending. These are that tooling system's tabulated limits, subject to the catalog's operating conditions; they are not allowable thicknesses for any tool described as “Z4.” [TRUMPF, Bending Tools catalog, edition 01/2025, p. 260](https://www.trumpf.com/filestorage/TRUMPF_Master/Products/Services/01_brochures/TRUMPF-bending-tools-catalog-EN.pdf)

Wilson Tool explains that standard offset tools can air bend different offsets when the required height is fixed but the angle is allowed to vary. That distinction matters at quotation: accepting a variable transition angle can enable a different tool solution, while a controlled angle and height together impose more constraints. Do not relax either requirement without checking the mating geometry. [Wilson Tool, Air Bending with Offset Tools](https://wilsontool.com/en-us/resources/air-bending-with-offset-tools-bending-technically-speaking)

AMADA also offers a **punching-tool** offset process described as raising a flange by the material thickness to permit overlap. This illustrates another manufacturing route; the product description does not establish unrestricted material, thickness, offset-height or surface-finish capability. Confirm those details for the installed machine and tool. [AMADA, Offset—Overlapping Assembly](https://www.amada.eu/hr-en/products/tooling/punching-tooling/punching-solutions/punching-tools-multiple-applications/offset/)

## Material, access and flat development

Supply the alloy, temper/condition, actual thickness range, finish and any restrictions on forming marks. Ask the supplier to check minimum radii, transition severity, grain orientation where relevant, springback, tool loading and clearance around existing flanges. A small offset is not automatically easy: two bend regions can interact, and short lands can restrict support or gauging.

The flat pattern must match the qualified forming process. Two visible bend angles and the offset height alone do not determine a reliable blank if bend radii and development assumptions remain unspecified. Use the selected CAD rule and shop's validated development data consistently. Avoid mixing a drawing's finished dimensions with an unrelated generic K-factor and treating the resulting blank as authoritative.

For a local flange joggle, review its runouts in three dimensions. Check interference with adjacent walls, hole distortion, remaining edge distance and access for a rivet set, welding tool or assembly fastener. The formed step can clear the mating sheet while the transition still collides with its edge.

## Original flush-overlap tolerance example

Assume two uniform sheets are intended to have flush outer faces. Define `h` as the inward displacement of the supporting flange's outer face from its unjoggled outer face. A mating sheet of thickness `t` seats on that displaced face. Ignore coatings and interfacial gaps for this first calculation. The mating outer face is proud of the reference by `e = t − h`.

For assumed dimensions `t = 1.50 ± 0.05 mm` and `h = 1.50 ± 0.10 mm`, the nominal mismatch is zero. The worst cases are:

- Maximum proud condition: `1.55 − 1.40 = +0.15 mm`.
- Maximum recessed condition: `1.45 − 1.60 = −0.15 mm`.

A nominal “offset equals thickness” condition therefore does not guarantee ±0.05 mm flushness. These are illustrative assumed tolerances, not a forming capability claim. Add the actual coating, adhesive/sealant or gap stack with its correct geometry and sign; decide whether the requirement applies before fastening, after clamping or on the completed assembly. Account separately for angular error and local waviness, which this one-dimensional stack does not represent.

## Release and inspection

Record the intended contact condition rather than requiring an assembler to force an uncontrolled offset into place. Inspect height from the named datum, then assess transition location, final-surface orientation, cracking, wrinkles and agreed marking limits. For a structural or sealed joint, the joggle does not by itself establish fastener strength, fatigue life, corrosion protection or leak tightness.

A useful manufacturing release includes the formed model, dimensioned critical interfaces, material/condition and thickness, final surface requirements, and agreed control of the flat pattern. If the shop proposes a different radius or transition angle, check the complete overlap and fastening arrangement before accepting it.

## Source editions

The FAA identifies FAA-H-8083-31B as its 2023 Airframe handbook. Ansys help prints Release 2025 R1. The downloaded TRUMPF catalog prints edition 01/2025 and material number 2968160 on its title-information page; its filename does not establish the edition. The cited AMADA and Wilson Tool pages do not state a technical revision date.

## Related reference

[Part features](index.md)