Sheet Metal CAD

How it works

1. Send the drawing, model, flat pattern, or photographs of the part.
2. We review the source and send a free quote within 12 hours.
3. Our engineering team builds the folded model and develops the flat pattern, and stops to ask whenever the source does not state what it needs to.
4. A second engineer verifies the model, then the files reach you by email or secure download link.

Steps 2 and 3 are where sheet metal work goes wrong, and they fail for different reasons.

Step 2 fails when a drawing looks complete and is not. Sheet metal prints carry a specific kind of incompleteness that other mechanical drawings do not. A fully dimensioned part view with every hole located and every flange length called out can still be undevelopable, because developing a flat pattern needs material, thickness, inside bend radius, and K-factor, and none of those are geometry. Legacy prints routinely omit all four. We check for them during quoting rather than during modeling, so a missing material callout is a question you answer before committing money.

Step 3 fails when a missing forming parameter gets filled in quietly. Ambiguity stops the job. Where the surrounding dimension chain leaves exactly one arithmetically possible value, that value is closed without asking, because that is arithmetic, not assumption. A value that merely looks plausible is still a guess. Assuming 1.5 mm because the part looks like 1.5 mm produces a blank that cuts cleanly, folds to the wrong overall dimension, and fails at assembly rather than at the laser. Open points come back batched as one written list, and queries pause the clock.

Flat pattern development

Developed length is not a geometric calculation. This is the single most common misunderstanding in outsourced sheet metal work, and it is why a flat pattern cannot be derived from a folded model alone.

Why the arithmetic does not close. When material is bent, the outer surface stretches and the inner surface compresses. Between them sits a layer that does neither, and the length of that layer is the developed length of the bend. If the neutral layer sat at mid-thickness, unfolding would be trivial. It does not. Under bending it shifts toward the inside of the bend, and how far it shifts depends on the material, its thickness, the inside radius, and how the bend was formed.

K-factor is the position of that layer, expressed as a fraction of material thickness measured from the inside surface. A K-factor of 0.5 would put the neutral layer at mid-thickness. Real values sit lower, commonly between about 0.3 and 0.5, and they are not a property of the material alone. The same steel at the same gauge yields a different K-factor under a different forming process.

Bend allowance and bend deduction are two ways of applying it. Bend allowance is the arc length of the neutral layer through the bend, and it is added to the flat lengths of the adjoining flanges. Bend deduction works from the outside dimensions instead, subtracting the difference between the outside setback and the bend allowance. Both describe the same physical fact. Which one a shop uses depends on how its drawings are dimensioned, and mixing the two conventions produces a blank that is wrong by roughly twice the material thickness at every bend.

The same 3D model produces different flat patterns for different fabricators. This is not sloppiness, it is physics. Air bending, bottoming, and coining move the neutral layer to different places. The width of the die opening changes the inside radius actually produced on the part, and the inside radius is an input to the developed length. A shop with wide tooling and a shop with narrow tooling, running the same material at the same gauge from the same model, will need different blanks to end up with the same finished part. Springback compounds this, since the amount of overbend needed to land on the target angle varies with material grade and temper.

The practical consequence is that a flat pattern is only correct for the shop and process it was developed for. A DXF that produced perfect parts at one fabricator can be out of tolerance at another.

When the source does not state material and gauge, the flat pattern cannot be developed at all. Not approximately, not provisionally. Every term in the calculation depends on inputs the drawing has not supplied, and the failure is quiet: the blank looks correct, cuts correctly, and folds to the wrong dimensions. Where a source drawing omits material, thickness, bend radius, or K-factor, we ask.

We work to your values, not to a generic table. A K-factor encodes the tooling and the process that formed the part, so a number lifted from a published table describes a shop that is not yours. Where you have gauge tables and a K-factor, those go into the model as given. Where you do not, we establish them from a sample part or from your fabricator via you, and confirm them with you before anything is developed.

What we deliver

Flat patterns as DXF. The file carries the developed outline, hole positions, and bend lines, developed to the forming parameters confirmed for your part. It is not prepared for a named machine, and that is deliberate. Kerf compensation, lead-ins, and nesting depend on the cutter, the material batch, and the nesting software in use, so they belong to whoever runs the machine. A DXF with kerf already applied is a file your fabricator has to undo.

A folded 3D model with an editable feature tree in SolidWorks, Inventor, or PTC Creo. Bends are bend features with radii and angles you can change, and the flat pattern updates when you change them. AutoCAD is delivered as a 3D solid instead, because AutoCAD has no parametric feature history for a tree to live in.

Neutral formats. STEP AP242 — geometry as standard. Full PMI, GD&T, and model-based definition available on request. Also STEP AP203 and AP214, IGES, and Parasolid X_T. Note that a B-rep solid arriving through a neutral format carries the folded geometry but not the sheet metal features, so the flat pattern does not regenerate from a STEP file.

2D drawings on request, as DWG, DXF, or PDF, dimensioned to ANSI Y14.5 or ISO 1101.

Bend tables where the part warrants one, listing bend sequence, angles, inside radii, and directions.

Assembly structure decided at quote stage. Either a mated assembly or individual parts. Assemblies run up to 1000+ parts.

Two-tier QC. Modeling by a specialist, verification by a second engineer, before anything reaches you.

One revision round is included per project, with additional revisions billed at the rate specified in your quote. Errors caused by our team are corrected at no charge within 30 days of delivery, separately from the included revision. Upon full payment you receive full ownership of the deliverables, and we retain no rights in them.

On file handling. An NDA is available on request and is signed before any files are shared. Source files are deleted from our systems within 90 days of project completion, and our production partner retains files under its own policy, typically no longer than twelve months. Uploaded files and delivered models are not used to train AI models, and partners are not authorized to do so on our behalf.

Single parts start at $125, small assemblies at $190, and complex enclosures at $500. See pricing.

When this gets difficult

No material or gauge callout. The most common gap in legacy sheet metal prints, and the one that stops everything. Thickness is an input to every bend calculation, and it cannot be inferred from the drawing, because a print of a 14-gauge bracket and a print of a 16-gauge bracket look identical. Where a sample part exists, thickness can be measured and confirmed with you. Where it does not, this is a question before modeling starts.

A flat pattern supplied without bend lines. A flat blank with holes and an outline defines a shape, not a part. Without bend lines, nobody can tell where the folds go, which direction each one turns, or what sequence they run in. Bend lines drawn without an up or down designation are only half the information, and a flange folded the wrong way produces a part that mirrors instead of mating.

Bend radii your tooling cannot produce. A model drawn with a 1 mm inside radius on 3 mm plate is geometrically valid and not formable, because minimum bend radius is a function of material and temper rather than a modeling choice. Bending across the grain direction rather than along it changes the minimum, and some alloys crack at radii that carbon steel handles without complaint. If a part has been designed to radii your shop cannot hit, the flat pattern will be wrong no matter how carefully it was developed.

Features too close to a bend. A hole placed within the bend deformation zone distorts into an oval when the flange goes up. A flange shorter than the minimum for the material and tooling cannot be gripped and will not form. Internal corners without bend relief tear. Each of these produces a model that passes every check in CAD and fails on the brake.

Geometrically valid is not the same as manufacturable. A folded model can be perfectly closed, watertight, and correctly dimensioned while describing a part no press brake can make, usually because the bend sequence collides with the tooling or with the part itself. The last bend on a deep enclosure is frequently the one that cannot be reached. Where we can see that a part is unformable as drawn, we say so at quote stage rather than delivering a file that satisfies the specification and not the shop.

What this costs you

Queries pause the clock. A print with no material callout, no bend radius, and a flange that looks too short will take longer than a complete drawing, and if a question sits unanswered for two days, delivery moves by two days. Batching them into one written list limits the interruptions without removing the wait.

A vendor who never asks anything will always look faster. He picks a gauge, applies a default K-factor, and delivers on schedule. The blank cuts cleanly. The error appears when a fabricator folds it and the overall dimension is out by several millimetres, at which point the material is scrap and the schedule is gone.

Who this is for

You have legacy sheet metal prints and no models. The parts still get made, the drawings are 2D, and every new supplier wants a DXF.

Your fabricator sends back blanks that fold to the wrong size. The flat patterns came from a model developed with forming parameters that do not match the shop actually running the job.

You are designing enclosures and need the flat patterns done properly. The 3D work is within your team's capacity and the development is not the part you want to spend the week on.

You are moving a part between fabricators. A flat pattern correct for one shop is not automatically correct for the next.

You have a physical enclosure and no drawings at all. That starts as reverse engineering and continues into this work once the geometry exists.

If what you have is general mechanical drawings rather than sheet metal parts, that is legacy drawing conversion instead.

FAQ

Do you use our K-factor or your own?

Yours, whenever you have them. A K-factor encodes the tooling and the process that formed the part, so a value from a published table describes a shop that is not yours, and a blank developed from it is wrong in a way that only appears on the brake. Send your gauge tables and K-factor and they go into the model as given. If you do not have them, we establish them from a sample part or from your fabricator via you, and confirm them with you before development starts.

Can you work from flat patterns only?

Yes, provided the bend lines are present with directions and the material and thickness are stated. A flat pattern with all three is enough to build the folded model and re-develop the blank to a different set of forming parameters. A flat pattern without bend lines is an outline, and reconstructing the folds from it means inferring where they belong, which is a guess rather than a reading. In that case we come back with a marked question rather than an assumption.

What if we do not know our bend radius?

It is recoverable, and it is worth recovering rather than defaulting. If you have a formed sample, the inside radius can be measured and confirmed. If you do not, your fabricator knows the tooling he runs and can supply it in one email. What we will not do is apply a plausible value silently, because inside radius feeds directly into developed length and an error there propagates through every dimension on the blank.

Can you produce DXF ready for our laser?

The geometry is right for your part and your tooling. The machine preparation is your fabricator's, and that is the correct division. Kerf compensation, lead-ins, and nesting depend on the specific cutter, the material batch, and the nesting software in use, so applying them upstream hands your fabricator a file to undo rather than a file to run. What arrives from us is the outline, the hole positions, and the bend lines, correct for the parameters confirmed for your part.

What about welded assemblies?

Weldments are handled as assemblies of individual sheet metal parts, each with its own flat pattern, plus the assembly model showing how they locate. Weld preparation and fit-up allowances need stating in the source or confirming with you, since they affect the developed dimensions of the parts either side of the joint. We deliver the files. The welding procedure itself sits with your fabricator.

Do we get a bend table?

Where the part warrants one, yes, listing bend sequence, angle, inside radius, and direction for each bend. For a simple bracket with two folds it adds little. For an enclosure where the bend order determines whether the part can be formed at all, the table is the document your brake operator actually works from, and it is worth requesting explicitly at quote stage.

How long does it take?

Simple work returns in 24 to 48 hours. Medium complexity runs 2 to 3 business days. Complex work runs 4 to 6 business days. Rush turnaround of 12 to 24 hours is available for files received before 11am, subject to availability. These ranges assume source material that states its forming parameters. A drawing with no material callout sits in the query queue rather than the modeling queue, since every query pauses the clock.

If you need the flat pattern in a format not listed here, see CAD format conversion, or send us the drawing for a quote.