Sheet-Metal Part Detailing and Flat Patterns Folded shape, flat pattern.

Formed part drawings

With dimensions in the folded state, which is how the part will be inspected.

Flat pattern development

With bend lines and bend direction identified, not merely implied by geometry.

Bend allowances and deductions

Applied to the parameters your fabricator supplies.

Material specification.

Type, gauge and finish, with the visible faces identified.

Hole and cut-out positions

Dimensioned in the flat state where fabrication needs them there, and in the folded state where inspection needs them there.

Bend sequence

Wherever the order is constrained by tooling access.

Weld and fastening preparation

Where applicable.

Finish requirements

Including which surfaces are exposed in the finished assembly.

Bend allowance depends on the material, the gauge, the inside radius, the tooling and the machine. The same nominal part formed on two different brakes with different tooling produces two different flat patterns, and only one of them is correct for your shop.

So flat patterns are developed to the parameters your fabricator supplies: material and gauge, inside radius, and either the k-factor or the bend deduction table actually in use.

Where those are not available, that is said rather than a generic figure being applied quietly. A generic k-factor produces parts that are close, which is worse than parts that are obviously wrong, because close parts reach assembly before anyone notices.

A first article should always be checked before a production run, whoever produced the pattern.

The difference matters and it is where generic sheet-metal detailing falls down on fixture work.

Visible surfaces.

Bend marks, tooling witness and material grain direction all show on a display fixture under retail lighting. On a machine guard nobody looks.

It has to receive something made from wood.

Connection points are positioned and toleranced for the panel, shelf or upright they will carry, which is a different exercise from positioning them for another metal part.

Finish adds thickness.

Powder coating builds up on every surface including the ones that were dimensioned for clearance, and that clearance is usually where a wood component was meant to sit.

Springback is real.

Formed parts do not exactly match nominal geometry. On a fixture assembly, that variance lands at the interface, which is why adjustment provision belongs in the detail rather than in the fitter’s judgement.

Flat pattern geometry exports as DXF for cutting. The formed parts sit inside the fixture assembly as one modelled set rather than as a separate metal package.

And the connection points those parts carry are detailed at the metal-to-wood interface, which is where a fixture usually fails if nobody owns it.

Fixture manufacturers with in-house or partnered metal fabrication. Millwork shops that added or bought a metal line and need drawings that match the new reality. Metal shops that took on wood and found the casework side harder than expected.

If your shop recently became a both-trades shop, this is the drawing problem you have been living between two vendors.