What Does a CAD Review Include Before 3D Printing?

The Short Answer

A printability review, often called a DFM review, checks whether a file will print well in the process and material you chose: format and units, a closed mesh, wall thickness, small features, overhangs and supports, orientation and material choice. Ours is done by an engineer, at no cost and with no obligation to order. It is a printability review, not engineering validation: it does not prove the part is strong enough, that it fits parts we have not seen, or that it meets a standard. Changing your CAD is separate design work, quoted with a fixed price and schedule before it starts.

Free Review, Paid Design Work, and What Stays With You

The line between the three is where most misunderstandings start, so here it is in one place.

File Checks: Format and Units

STEP, IGES and 3MF files carry their units. The 3MF Core Specification, for example, defines a unit attribute on the model (micron, millimeter, centimeter, inch, foot or meter, defaulting to millimeter). STL and OBJ files carry no units and are always read as millimeters, so a part drawn in inches arrives 25.4 times too small. The quote page shows the measured size in the Model size panel under the 3D viewer. If it is wrong, declare the file's authoring unit (mm, cm or in), which rescales and reprices the part; the uploaded file itself is never altered. See CAD file formats for 3D printing and STL units for the details.

File Checks: A Closed Mesh

A printable mesh has to describe one closed surface. The Library of Congress format record for STL describes the vertex-to-vertex rule: each triangle shares an edge with each of the triangles next to it. Gaps, flipped faces and overlapping shells break that rule, and a reviewer flags them rather than guessing what the surface should have been. The reliable fix is upstream, in the CAD: export solids, not surfaces, and re-export rather than patching the mesh. How to prepare CAD files covers export settings.

File Checks: Geometry

• Wall thickness: walls too thin for the chosen process or material to print reliably or survive handling.
• Small features: pins, ribs, holes, text and gaps near the limit of what the process resolves, which may not print as drawn.
• Overhangs and supports: university design guides give a 45 degree rule of thumb for unsupported overhangs on FDM. Supports leave marks where they touch. FDM parts ship with support material removed, and SLA support marks on the bottom face are sanded by default.
• Orientation: the build direction changes strength, surface finish and where supports land. One filament maker's PETG datasheet, for example, lists printed bending and impact strength separately for the X-Y and Z directions, with lower values in Z (see print orientation and strength).
• Size: the largest one-piece parts are FDM 350 × 320 × 325 mm and SLA 353.2 × 198.7 × 400 mm. A part that fits no orientation gets no instant price and goes to large-format review, where it can be split into sections and assembled (see large-format 3D printing).

Material and Process Discussion

The review asks what the part has to do: carry load, sit outdoors, stay near heat, flex, seal or look finished. From that, the engineer suggests a process (FDM or SLA) and a material from the materials catalog. The typical tolerances published for each process are FDM ±0.2 mm and SLA ±0.1 mm, as general guidance that depends on geometry. If a requirement sits at the edge of those numbers, the review says so. For background before you ask, read how to choose a 3D printing material and FDM vs SLA.

Assembly Assessment

A review can only judge a fit between parts it can see. Send every printed part of an assembly, and the drawings or datasheets of purchased parts they mate with. The reviewer then looks at clearances between parts, snap and press fits, and holes for threaded inserts. Insert holes deserve attention: SPIROL, an insert maker, says hole size is critical to insert performance, notes that printing tolerances often exceed the hole tolerance it recommends, and recommends a printed boss of at least 1.5 times the insert's knurl diameter. Threaded insert installation is offered as post-processing on FDM parts. For the design side, see heat-set inserts and threads, snap-fit and press-fit assemblies and working prototype assemblies.

When the File Needs Changes

The review reports what to change; it does not change your file. You can edit the CAD yourself and upload the new revision, or ask for CAD modifications as a separate service. 3D modeling services, which cover design and CAD changes, 3D modeling and reverse engineering, are quoted per project with a fixed price and schedule before work starts, with no obligation to proceed. Keep the review's notes with the revision they apply to, so the next upload is checked against the right version.

What a Review Cannot Tell You

ISO/ASTM 52910, the general design standard for additive manufacturing, states that it gives general guidance and identifies issues but does not supply specific design solutions or process- or material-specific data. A printability review works the same way. Datasheet values do not settle it either: that same filament datasheet says its typical values are for reference and comparison only, not design specifications, and that a printed part's performance also depends on its design, printing conditions and environment.

• Whether the part survives its loads, temperatures, fatigue or impacts. That takes testing on printed parts (see specifying parts for validation testing).
• Whether it fits parts that were not sent with it.
• Whether it meets a code, a regulation or a customer specification.
• Whether a tolerance tighter than the published guidance will hold on every part.

What to Send for a Useful Review

• The file in STEP where possible, or STL, OBJ or 3MF with the authoring unit stated.
• Every printed part of the assembly, plus drawings or datasheets of purchased mating parts.
• What the part does and where it lives: loads, heat, outdoor exposure, chemicals.
• The dimensions and fits that matter, with the tolerance each needs.
• The quantity you expect to order, and any material you already prefer.
• Anything you already know is a risk, so the reviewer looks there first.

How to Ask

Upload the file on the quote page and ask for a printability review, or reach the team through the contact page. A real person answers email within one business day. The review is free and carries no obligation to order, so it is worth asking before the first print rather than after a failed one.