June 10, 2026

Best File Formats for CNC Quoting (STEP, IGES) — 2026 Guide

Learn the best file formats for CNC quoting—STEP, IGES, and BREP—plus AP214/AP242 tips and PDF must-haves. Get faster, more accurate quotes now.

TL;DR

STEP is the best file format for CNC quoting. It preserves full solid geometry, works with every CAM system, and gets you the fastest, most accurate quote. Always pair it with a PDF drawing when tolerances or surface finishes matter. IGES works as a fallback but often has surface gaps that slow things down. BREP is accepted by some platforms, including FrankWorks, and preserves solid geometry similar to STEP.

Who This Guide Is For

If you’re a procurement specialist, maintenance engineer, or operations manager about to upload a CAD file for a CNC machining quote, the file format you choose directly affects how fast you get a price, how accurate that price is, and whether you’ll face delays before production starts.

This guide covers the best file formats for CNC quoting (STEP, IGES, BREP, and others), explains the practical differences between them, and tells you exactly what to do before hitting upload.

Upload your CAD file to get instant pricing and a defined lead time from vetted Canadian machine shops.

Quick Answer: Use STEP

STEP (Standard for the Exchange of Product Data) is the universal recommendation. Every CNC shop, every CAM system, and every instant quoting platform reads it. It preserves mathematically precise solid geometry, meaning faces, edges, and volumes come through intact with nothing lost.

Practitioners on the Practical Machinist forum confirm this overwhelmingly. One machinist noted that roughly 50% of the work from their shop is done from STEP files. Another reported that STEP imports in about one-tenth the time an IGES file does.

The formula is simple: STEP file + PDF drawing = fastest, most accurate CNC quote.

The PDF carries the information a 3D model can’t: tolerances, surface finish callouts, thread specifications, and datum references. The STEP file carries the geometry. Together, they give the shop everything needed to quote and program your part without a single email back and forth.

File Format Comparison Table

Before going deeper into each format, here’s a quick reference for choosing the best file formats for CNC quoting:

Format	Extensions	CNC Quoting Suitability	Key Trait
STEP	.stp, .step	✓ Best choice	Full solid geometry, ISO standard
IGES	.igs, .iges	△ Acceptable fallback	Legacy format; may have surface gaps
BREP	.brep	✓ Accepted by some platforms	Open CASCADE boundary representation
Parasolid	.x_t, .x_b	✓ When kernel matches	Highest fidelity if both sides use Parasolid
STL	.stl	✗ Not for CNC	Mesh approximation; for 3D printing
DXF	.dxf	✗ 2D only	For laser/waterjet profiles
Native CAD	.sldprt, .ipt, .prt	△ Convert first	Requires matching CAD license to open
PDF	.pdf	✓ As supplement	Tolerances, GD&T, finish callouts

The rest of this guide explains why each format lands where it does and what the practical consequences are for your quote.

STEP: The Standard for CNC Quoting

What It Is

STEP stands for Standard for the Exchange of Product Data. Defined by ISO 10303, it’s an international standard for exchanging 3D product model data. It’s an open format, meaning no proprietary license is needed to read or write it.

Why It’s the Best Format for CNC Quotes

A STEP file contains true solid geometry with exact mathematical surfaces. When a CNC shop or quoting platform receives a clean STEP file, the geometry translates directly into toolpaths without reconstruction, healing, or guesswork.

Here’s what that means in practice: a contract manufacturer receives an RFQ for 50 aluminum housings with a clean STEP file attached. The solid geometry is intact, topology is clean, all features are present. Quotation takes about 45 minutes, toolpaths generate cleanly, and the order can be placed the same day.

Compare that to a problematic file that needs repair work. Each hour of additional programming time is a direct cost, either charged explicitly as a programming fee or built into the quoted part price. A clean STEP file means a lower price and a faster turnaround. It’s that straightforward.

When comparing quoting approaches, the all-in pricing model makes it even more important to start with a clean file, because there are no hidden line items to absorb rework.

STEP Application Protocols: AP203 vs AP214 vs AP242

Not all STEP files are identical. The format comes in several “Application Protocols” that determine what data the file carries beyond basic geometry. For a deeper walkthrough, see this STEP AP242 guide and CNC drawing checklist.

AP203 was originally developed for aerospace and defense, where design version control matters. It handles mechanical CAD data for individual parts and assemblies but carries minimal non-geometric data. No colors, no material properties.

AP214 includes everything in AP203 plus colors, layers, geometric dimensioning and tolerances (GD&T), and design intent data. It’s considered a direct extension of AP203 and is the most commonly used protocol for CNC quoting today.

AP242 is the newest protocol, merging the strengths of AP203 and AP214 while adding complete support for Product and Manufacturing Information (PMI). This enables Model-Based Design, where all the annotation that traditionally lives on a 2D drawing is embedded directly in the 3D model. AP242 also supports advanced manufacturing processes including CNC machining and additive manufacturing.

One important note: AP203 and AP214 were officially deprecated with the publication of AP242 in 2014 (ISO lifecycle stage 95.99). In practice, though, every major CAD package still reads and writes all three versions.

What to export for CNC quoting: AP214 is the safe default. It carries geometry plus useful metadata like colors and layers. If your CAD software offers AP242 and your part has complex GD&T, use that instead. AP203 works fine for simple parts, but there’s no reason to choose it when AP214 is available.

IGES: A Legacy Fallback

What It Is

IGES stands for Initial Graphics Exchange Specification. Developed in the 1970s by a US Air Force and NIST collaboration, it was the first neutral CAD exchange format and dominated data exchange for decades. The last version (5.3) dates to roughly 1996. It is now a legacy format, though it remains in use where older software infrastructure persists.

Why It’s Not the First Choice

The core problem with IGES is that it’s primarily geared toward surface geometry and wireframes rather than true solid models. When you export a complex part as IGES, the file often contains surface patches that don’t quite meet up. Small gaps between patches, misaligned edges, overlapping surfaces. These errors translate directly into toolpath interruptions or unwanted cutter marks during machining.

Machinists have a nickname for the format. Practitioners on the Practical Machinist forum report hearing IGES called “I Guess” for over a decade, because the file quality is unpredictable. You guess whether the geometry will import cleanly. You guess whether the surfaces are actually closed.

The Cost of Surface Gaps

When a CNC shop receives an IGES file with surface gaps, they need to perform geometry healing before programming can begin. This means manually closing gaps, stitching surfaces, and verifying that the repaired geometry actually matches the designer’s intent. That takes time, and time is money on a quote.

For buyers, this usually shows up in one of two ways: a higher quoted price (to cover the programming risk) or a longer lead time while the shop contacts you to clarify geometry issues.

When to Use IGES

Use IGES only when STEP is not available from your CAD software. Some very old CAD systems or legacy files may only export IGES. In that case, validate the solid after import and confirm geometry is fully closed before submitting for a quote.

If you’re weighing whether to invest in converting old files, consider the cost to manufacture a single part. The savings from cleaner files on repeated orders add up quickly.

BREP: The Format Most Guides Skip

What It Is

BREP stands for Boundary Representation. A .brep file stores a 3D model using the boundary representation method from Open CASCADE Technology (OCCT). The structure consists of topological components (faces, vertices, edges) and the geometric links between them (surfaces, points, curves). It contains full three-dimensional solid data including edge and face triangulations.

Boundary representation as a concept actually underpins both STEP and Parasolid. In the late 1980s, a project called CAD*I developed a standard representation that became one of the foundations for STEP’s solid model format. The .brep file extension specifically refers to the Open CASCADE implementation of this concept.

When BREP Matters for CNC Quoting

BREP is far less common than STEP or IGES in the broader CNC industry. Most shops don’t advertise it as an accepted format. But if your CAD workflow uses Open CASCADE or a tool built on that kernel (FreeCAD is a notable example), you may already be generating .brep files.

FrankWorks accepts BREP files alongside STEP and IGES for instant quoting. If you work in a BREP-native environment, this means you can skip the conversion step entirely and upload directly for pricing.

For everyone else, STEP remains the better choice simply because of universal compatibility.

Other Formats: When They Work and When They Don’t

Parasolid (.x_t, .x_b)

Parasolid is the geometric modeling kernel behind many major CAD systems, including Siemens NX, Solid Edge, and SolidWorks. Files exported in Parasolid format retain the highest fidelity of complex features like Boolean operations, fillets, and lofts because the math stays in its native form.

The catch: Parasolid is best when the receiving side also uses a Parasolid-based system. If you know your CNC shop or quoting platform uses SolidWorks or NX, Parasolid can be an excellent choice. If you don’t know, STEP is safer.

STL (.stl): Not for CNC Machining

STL stores geometry as a mesh of triangles approximating the surface of a part. It’s fine for 3D printing, where the printer slices a mesh layer by layer. It is not suitable for CNC machining.

The triangulated surface introduces faceting that compromises tight tolerances and smooth curves. Submitting an STL for CNC work forces the shop to reconstruct surfaces, manually identify features, and verify toolpaths against approximated geometry. That reconstruction time gets billed to you.

If someone asks you to submit an STL for a CNC quote, find a different shop.

DXF (.dxf): 2D Cutting Only

DXF defines 2D profiles, contours, holes, and planar paths. It’s the standard format for sheet metal fabrication, laser cutting, and waterjet work. It has no role in 3D CNC milling or turning quotes.

Native CAD Formats (.sldprt, .ipt, .prt)

Native files from SolidWorks, Inventor, Creo, and similar platforms contain the richest data, but they require the receiving party to own a matching CAD license. Most quoting platforms and shops prefer STEP because it’s license-free and universally readable. Always convert to STEP before uploading unless the platform explicitly requests native files.

PDF Technical Drawings: The Essential Companion

A STEP file carries geometry. A PDF drawing carries everything else. Tolerances, surface finish requirements, thread callouts, datum references, material specifications, and special instructions all belong on the drawing.

For all conventional machining, the best practice is to upload a STEP file along with a 2D PDF. To learn what belongs on that drawing and how to prepare it, see this guide on how to prepare a CAD drawing for CNC machining.

File Export Mistakes That Slow Down Your Quote

Even when you choose the right format, a handful of common export errors can delay your quote or produce an inaccurate price. These issues come up repeatedly in machinist forums and shop floor discussions.

Wrong Units

A part designed in millimeters but exported in inches will be 25.4 times too small. Or vice versa. Check your CAD software’s export settings before saving. This is the single most common and most preventable error.

Multi-Body Files

Each part should be its own STEP file. Multi-body exports, where several distinct components sit in one file, confuse automated quoting engines. The system can’t tell which body is “the part” and which are fixtures, tools, or adjacent components.

Assembly Data Left In

Export only the part body. Remove assembly references, mates, and constraints before exporting. Leftover assembly data bloats the file and can introduce geometry that doesn’t belong to the part being quoted.

Suppressed Features

If you suppressed a hole, pocket, or chamfer during design iterations, un-suppress it before export. Suppressed features won’t appear in the STEP file, meaning your quote will be based on incomplete geometry. The shop will machine the wrong thing.

Outdated Revisions

Name your files with the revision. Something like bracket-rev-C.stp avoids confusion when you’ve sent multiple versions. Shops quoting from the wrong revision waste everyone’s time.

Not Verifying the Export

Always open your exported STEP file in a free viewer before sending it. Missing faces and broken surfaces are more common than you’d expect, especially after complex Boolean operations. Catch them before the shop does. This saves a round trip of emails and potentially days on your timeline.

For a complete walkthrough of file preparation, the CNC machining file prep guide covers each step in detail.

What If You Don’t Have a CAD File?

Not every part comes with a digital model. Legacy equipment, lost drawings, worn components from machines that predate CAD entirely. These are common situations in maintenance and MRO environments, especially in mining, aggregate processing, and food manufacturing where equipment runs for decades.

None of the top-ranking guides for “best file formats for CNC quoting STEP IGES” address this scenario, but it’s one of the most frequent challenges industrial buyers face.

The solution is reverse engineering: creating a STEP file from a physical part, a set of measurements, or even photographs. Once the model exists, it goes through the same quoting workflow as any other CAD file, and you have a digital record for future reorders.

Submit photos for reverse engineering if you have a broken or worn part but no drawing. FrankWorks offers a reverse engineering service where the fee is credited if you proceed with manufacturing.

How File Format Affects Instant Quoting Platforms

Modern CNC quoting platforms use automated geometry analysis to generate pricing. You upload a CAD file, the system analyzes geometry, material, and quantity, and returns a price with a lead time. No emails, no waiting days for a callback.

The best file formats for CNC quoting on these platforms are the same ones that work best for manual quoting, just more so. Automated systems are less forgiving than a human programmer. A surface gap that an experienced machinist might heal in ten minutes can cause an automated system to reject the file entirely or produce an inaccurate quote.

STEP files parse the fastest and most reliably. IGES files may require geometry healing that the platform either handles automatically (adding processing time) or flags for manual review (adding days). STL files are often rejected outright for CNC quoting.

FrankWorks accepts STEP, IGES, and BREP uploads (up to 50 MB) for instant pricing with defined lead times. The platform routes production to vetted, Canadian-owned machine shops and provides all-in pricing that includes shipping.

Quick Checklist Before You Upload

Before submitting your file for a CNC quote, run through this list:

Export as STEP AP214 or AP242. AP214 is the safe default. AP242 if you need embedded GD&T.
One part per file. No multi-body exports, no assembly data.
Verify units. Millimeters or inches, confirmed in your export dialog.
Un-suppress all features. Every hole, pocket, and chamfer should be visible.
Include revision in the filename. Example: housing-rev-B.stp.
Attach a PDF drawing. Include tolerances, surface finish, thread specs, and material.
Open the STEP in a viewer. Check for missing faces, broken edges, and unexpected geometry.
Upload and get your quote. Get instant pricing from FrankWorks with a defined lead time and all-in cost.

Frequently Asked Questions

Is STEP or IGES better for CNC quoting?

STEP is better in almost every case. It preserves full solid geometry with mathematical precision, while IGES often produces surface gaps that require manual repair. Machinists report that STEP imports roughly ten times faster than IGES. Use IGES only when your CAD software cannot export STEP.

Which STEP application protocol should I use?

AP214 is the best default for CNC quoting. It carries geometry plus colors and layer data. AP242 is technically superior and supports embedded GD&T, but AP214 is universally supported and sufficient for most parts. AP203 works but carries less metadata than either alternative.

Can I submit an STL file for a CNC machining quote?

You can, but you shouldn’t. STL files store approximated triangle meshes, not solid geometry. Submitting STL for CNC machining requires the shop to reconstruct surfaces and manually identify features, which adds programming time and cost to your quote. Always convert to STEP first.

What is a BREP file and can I use it for CNC quoting?

BREP (Boundary Representation) is a 3D format from the Open CASCADE Technology ecosystem. It stores solid geometry similar to STEP, including faces, edges, and vertices. It’s not as widely accepted as STEP across the industry, but some platforms (including FrankWorks) accept BREP uploads for instant quoting.

Do I need to send a PDF drawing with my STEP file?

Yes, for any part with specific tolerances, surface finish requirements, thread callouts, or material specifications. The STEP file carries geometry only. The PDF drawing communicates everything the shop needs to know beyond shape and size.

What if I have a part but no CAD file at all?

This is a reverse engineering scenario. A service provider can create a STEP model from your physical part, measurements, or photographs. Once the CAD file exists, it enters the standard quoting workflow and gives you a digital record for future orders.

Why does my file format affect the quoted price?

Every minute a machinist spends repairing geometry, healing surface gaps, or reconstructing features from a mesh is programming time that gets passed on to you. A clean STEP file minimizes that overhead, resulting in faster quotes and lower prices. A problematic file increases risk, and shops price that risk into the quote.

What file size limits should I expect for CNC quoting uploads?

FrankWorks accepts files up to 50 MB. Most STEP files for individual machined parts fall well within this limit. If your file is unusually large, check whether assembly data or unnecessary detail is inflating the size.