A large proportion of the delays in bureau 3D printing happen before anything reaches a machine. The file arrives, it cannot be printed as supplied, and the job goes into a back-and-forth that adds days. Most of these problems are avoidable and take minutes to check.
Watertight geometry
A printable model must describe a fully enclosed solid. Slicing software has to determine, for every point, whether it is inside or outside the object, and it cannot do that if the surface has holes in it.
Non-manifold geometry is the usual culprit: edges shared by more than two faces, internal faces left inside a solid, vertices that appear joined but are fractionally apart. These are invisible when you look at the model and fatal when you slice it.
Most CAD packages have a mesh check or repair function, and there are free tools that do nothing else. Run one before sending. If it reports errors it cannot fix automatically, that usually indicates a modelling problem worth going back to rather than patching.
Units and scale
The STL format carries no unit information. It stores numbers, and the receiving software assumes what those numbers mean — usually millimetres.
A model built in inches and exported to STL will arrive 25.4 times too small. This is one of the most common errors in bureau work, and because the resulting object is technically printable, it sometimes gets all the way to a finished part before anyone notices.
State the intended dimensions in your email. A single line saying the part should be 84mm across the base lets the bureau verify the scale in seconds.
Export resolution
STL approximates curves with flat triangles, and the export settings control how many. Too few and curved surfaces print with visible faceting. Too many and the file becomes enormous and slow to process without any visible improvement.
Most CAD packages express this as a chord height or deviation tolerance. Somewhere around 0.01mm to 0.05mm suits most work. If your exported file is over about 100MB for a modestly sized part, the settings are almost certainly too fine.
Where architectural and design exports go wrong
Models coming from architectural software need particular care, because that software is built to produce drawings rather than solids. Walls are often single surfaces with no thickness, objects intersect rather than being joined, and imported furniture blocks carry geometry of wildly varying quality.
Anything intended for print needs real thickness everywhere — typically at least 1mm to 2mm depending on scale and process — and overlapping elements should be properly unioned. Studios that regularly produce physical models from their architectural visualisation work usually maintain a separate simplified model for printing rather than trying to export the documentation model, which saves considerable frustration.
Orientation and the parts that will not survive
Layer adhesion is weaker than the material itself, so a printed part is stronger across layers than along them. A thin projection printed horizontally will snap where the same feature printed vertically would hold.
You do not need to orient the file yourself — the bureau will usually do it better — but flagging which features are structurally important lets them make the right decision.
Also check minimum feature sizes. Detail below roughly 0.4mm on FDM will not resolve, and text embossed less than about 0.5mm proud will disappear.
What to send with the file
A short covering note prevents most queries: the intended overall dimensions, the material or properties you need, whether the part is functional or visual, which surfaces matter cosmetically, any critical tolerances, and the quantity.
Where fit matters — a part that has to mate with something existing — say so explicitly and supply the mating dimensions. Fit issues are the most common cause of a reprint, and they are almost always a communication failure rather than a printing one.
The formats worth considering
STL remains the default and is fine for most work. 3MF is a better format where it is supported, carrying units, colour and material information that STL cannot. STEP is preferable where the bureau may need to modify geometry, since it preserves the underlying solid rather than a mesh approximation.
If you have the option, sending both an STL and a STEP file removes a whole category of problem.