File for 3D printing: STL, OBJ and common errors

Introduction

One of the most common causes of delays in 3D printing is not the machine, but the file. A model can “look good” on screen and still be unprintable, or require corrections that make the job more expensive. If you want a quick quote and a print that works the first time, here is what you need to know.

At Vanco Studio we provide 3D printing in Girona in both FDM and resin. And the difference between a smooth-running project and one with problems usually comes down to two things: the correct format and a model prepared for real manufacturing.

Valid formats for 3D printing: STL and OBJ

For most jobs, the most common formats are STL and OBJ. Both describe the geometry of the part and are compatible with the slicing programs (slicers) used to prepare the print.

STL

It is the de facto standard in 3D printing. It represents the part as a mesh of triangles. It works very well for printing, but does not store “parametric” dimension information (like an editable CAD file), so ideally it should be exported with good mesh quality and the correct scale.

OBJ

This is also a mesh format. It is widely used when the model comes from 3D software (artistic modelling) or when certain model properties need to be retained (for example, groups or additional information). For printing, the important thing is still that the mesh is closed and the geometry is clean.

Many projects also use CAD files such as STEP when available, because they allow dimensions to be adjusted with greater control before exporting to a mesh. If you are unsure what to send, we will review it with you before printing.

Common errors in 3D models that prevent printing (or make it more expensive)

• Model without a true “solid”: the mesh is not closed (holes) and the slicer cannot determine what is inside and outside.
• Incorrect scale: a part sent in millimetres when it was intended to be in centimetres (or vice versa), so the final size does not match.
• Walls that are too thin: the design does not have sufficient thickness for the chosen technology and breaks or does not print properly.
• Details that are too small: text or fine reliefs that will not be visible at that size, especially in FDM.
• Impossible overhangs: geometry that requires complex supports or leaves marks on critical surfaces.
• “Zero” fits: parts that should assemble together with no tolerance, then do not fit or are forced.
• Inverted geometry or incorrectly oriented faces: the file is effectively “inside out” at mesh level and causes slicing errors.

What to check before sending a file for printing

If you want to avoid corrections and speed up the quote, check these points before sending it:

• Final dimensions: confirm the actual size of the part and the unit (normally mm).
• Closed model: it should be a solid with no holes, no loose surfaces and no meaningless “floating” parts.
• Minimum thickness: define walls and details with enough thickness for the final use (decorative or functional).
• Orientation and critical areas: identify faces that must remain visible or have the best finish.
• Fits and tolerances: if there is assembly, leave realistic clearances according to material and technology.
• Final use: explain whether the part is aesthetic, a test or functional (load, screws, temperature, indoor/outdoor).

With this information, the quote is more accurate and the final result is better aligned with what you expect.

What to do if you do not have a 3D model

It is very common to have a clear idea but no file. In that case, the most practical approach is to start from references and turn them into a manufacturable model: a dimensioned sketch, photos, an existing part that needs to be replicated, or even a base model that needs adapting.

In the workshop, it often makes no sense to “design from scratch” if a valid starting point already exists. The professional approach is to normalise it: adjust dimensions, reinforce weak areas, correct tolerances and leave the file ready to print without surprises.

If you need that part of the process, you can use our technical design service (vector and 3D) for manufacturing. The idea is that you tell us what the part needs to do and we prepare the file so it can be printed properly, in FDM or resin depending on the case.

Before printing, the most cost-effective step is to validate the file: correct format, actual dimensions and a model prepared as a solid. A file that is “almost right” can turn into several tests, and that is always more expensive than reviewing it in time.

If you want, we can review your STL/OBJ or create the model from your idea. Write to us on WhatsApp or via contact and we will advise you according to your project.