3D Print File Checklist

STL is accepted everywhere. Use STEP when your bureau needs to modify orientation or check features. For metal DMLS, STEP is strongly preferred. When in doubt, send both.

Open the exported STL in a viewer and confirm the bounding box dimensions match what you expect in mm. If the model looks like it's 25x the right size, you exported in inches instead of mm.

Low-resolution export creates visible flat facets on curved surfaces — the printer faithfully reproduces them. Set tessellation deviation to 0.01–0.05mm in your CAD export dialog.

Extremely high-res STL files can crash slicers. If your file is over 50MB, reduce tessellation slightly — the print resolution is limited by the machine, not the file resolution.

A manifold (watertight) mesh is required for slicing. Run Meshmixer's Analysis > Inspector or PrusaSlicer's repair tool. CAD exports from Fusion 360, SolidWorks, or Onshape are almost always manifold — issues usually come from Blender or ZBrush exports.

Two overlapping bodies in an assembly don't automatically merge — slicers may print them as separate shells with weak internal boundaries. Boolean-unite intersecting bodies in CAD before exporting.

Every face must belong to a closed solid, not float as an orphaned surface. Surface modeling workflows (as opposed to solid modeling) often leave zero-thickness geometry that can't be physically printed.

Text below 3–4mm height disappears on FDM. Pin features thinner than 1mm break off post-processing on most technologies. Thin ribs, logo engraving, and fine embossing may not survive printing — verify with the bureau before finalizing.

For a 0.4mm nozzle: design walls at 0.8, 1.2, 1.6, or 2.0mm. A 1.0mm wall produces one partial-width extrusion line that's weaker than a proper two-line 0.8mm wall. For structural walls, 1.6–2.0mm is safer.

Resin can print 0.5mm walls but they're fragile and prone to breaking during washing and curing. Keep structural features at 1mm+. Purely decorative fins or lattice members can be thinner if they're not load-bearing.

SLS requires no supports so walls can be designed thinner than FDM without orientation concerns. However, very thin walls on large parts can warp during the slow cooling phase. 1.0–1.5mm gives a good safety margin.

Metal shrinks and warps during stress relief post-processing. Thin walls distort under residual stress. Critical features like bearing seats and mating surfaces should be 2.0mm+ and may need post-machining to hit tight tolerances.

3D printers don't hit nominal dimensions exactly. For shaft-in-hole fits: add 0.3–0.5mm clearance per side for FDM, 0.15–0.25mm for SLA or SLS. Parts designed at exact nominal dimensions rarely fit correctly straight off the printer.

Tight fit classes are sensitive to material shrinkage, which varies by machine and batch. Flag any snap, press, or interference fit in your order notes and ask the bureau if they want to run a test pin before the full order. This is standard practice on first-article work.

If certain dimensions are non-negotiable (a 10.00mm bore diameter, a specific wall thickness at a load point), list them explicitly in your order. Bureaus can orient and support the part to optimize accuracy on dimensions you call out.

If you know what you want: state it. If you're flexible: say so and describe the part's function. A good bureau will recommend the right process for the job — but they need context. "Make it strong and cheap" isn't enough; "bracket that holds 5kg static load, indoor use" is.

Order all the units you anticipate needing in the near term. Running a second batch means another full lead time and setup. For SLS and metal, batching saves significantly on per-unit cost. For FDM, multiples on one plate are often priced together.

Don't order on standard lead time and then ask for rush delivery later — it costs more and may not be possible. State your deadline when you place the order. Bureaus can plan queue position and shipping method accordingly.

As-printed, sanded, primed, painted, dyed, bead-blasted, or electroplated — specify what you need. If finish doesn't matter, say so. Some bureaus default to light post-processing that adds cost and time if you didn't ask for it.

For FDM and SLA, the orientation of the part on the build plate directly affects which surfaces have the best finish. If one face needs to look smooth, note it. If a load axis must run in XY (not Z), note that too. Bureaus will accommodate when asked.

If you're not sure whether a thin wall or long unsupported span will print successfully, say so in the order. Bureaus would rather catch a potential issue upfront than reprint after the fact. Most are happy to review the file and flag concerns before they start.