CAD File Guide

Although your 3D CAD file may look great on screen, many problems can still exist that need to be resolved before it can be recognised as a solid object and be ready to print.

In order for us to provide a quote or begin 3D printing, we would need to receive your file in .STL format. This format can be exported from almost all CAD software packages.

The following is a list of basic guidelines on how to produce a successfully 3D printable CAD file. Keeping these tips in mind will help make creating your CAD file much more efficient and help to avoid additional file fixing charges.

Solid Objects

In order for an object to be 3D printable, it needs to be drawn as a ‘solid object’.

This means that all surfaces and polysurfaces must be closed. For instance, the diagram on the left shows the difference between a surface and a solid.

Surfaces contain no volume, meaning it will not be recognised as an object. It is only by giving each surface a thickness that it will it then become a printable CAD file.

Missing Surfaces

The model on the left is missing one of its surfaces. This creates a hole in the model, therefore it cannot be 3D printed. To make this printable, the hole must be closed for it to become a solid object.

A simple way to think about a solid object is to imagine it filled with water. If it has holes, gaps or missing surfaces, the water will escape. A 3D printable model will therefore need to be ‘watertight’.

Inverted Normals 

When designing in a surface modelling software, it is possible to draw surfaces the wrong way up. This is known as an inverted normal. When this occurs it means the object will not be interpreted as a solid part.

Most CAD of File Fixing software will have an option to inform you which surfaces are inverted and offer you a method to correct this.

Holes & Unconnected Edges

Holes or unconnected edges are a very common error. This often occurs when there are small gaps between surfaces. Fill or stitch these together to make sure the object is sealed to become watertight.

Overlapping surfaces

Any duplicate or overlapping surfaces must be deleted.

Errors occur when multiple surfaces are applied in the same place. Some CAD and file fixing software will be able to visualise this and is easy to correct.


All objects that share the same space must be made into one single entity.

Any data that exists inside another object must be removed. This can often be found and fixed with the Boolean Union tool.

Floating Objects 

This is common occurrence, particularly within architectural models, when objects are not joined together. If objects are not connected in the CAD  file, then each piece will be printed as a separate object.

For instance the diagram on the left shows a set of treads that are not connecting to the stair stringer. These treads would have to be extruded into the column and unified to ensure that they are all printed as one piece.

Shared Edges

Objects that are meant to be touching need more than just a shared edge to bond together. They will need a volume to slightly overlap to actually bond them together.

For example, the image on the left shows a set of stairs. When the stairs are printed they would not have enough contact to remain as one piece, just as they would in real life. Instead, you should merge each step into the other, or create an under-structure.


When creating parts that need to fit around each other, you must include a clearance. Different machines have different clearances, so you will have to check the design guide for your preferred 3D print material.

Problems can also occur when designing objects or details too close together. Parts can often bond together or become impossible to remove powder from, so please check the design guide for your preferred printing method.

For information on the types of clearances required with Nylon SLS, you might like to take a look at our Nylon Fabric Samples.

Rigidity / Stiffness

Each material its own strengths and properties. So when you have chosen your preferred material, it is important to think about how thick it needs to be in order to provide your desired rigidity.

Without this consideration as you design, parts may flex or even break after they are printed.

For information on the strength and flexibility of Nylon SLS, you might like to take a look at our Nylon SLS Thickness Sample.

Trapped Powder

Small hollow parts can be problematic when it comes to removing the unsintered or unbinded powder. We do our best to flag this problem before printing, but this can delay the production time.

We have several techniques to avoid this, so let us know if this is a concern.


It is very important to consider the scale when 3D printing. Not only does this have a big impact on the cost, but it may be that the desired size of your object will not fit within the build chamber of your chosen 3D printer.

If the size exceeds the size of the build chamber, then it could be possible to print the object in separate parts and assemble the parts afterwards. However, if your object needs to be scaled down, then some areas may become too small to print.


Once you have finished designing your model in CAD you will need to save it as an .STL file. This file type creates a mesh that forms the shape of your object.

Try to keep the file size down, by choosing an appropriate resolution. The resolution should be high enough so that you will produce a smooth non-facetted model, however not so high that it exceeds the resolution of the printer and simply produces an extremely large file.

Check your File

Once you have finished your CAD design, try to check and view the .STL. If you can identify any issues then try and fix them before sending us the file.

You can use the following file fixing software to check your .STL file.

If you can’t resolve all of the problems that you may encounter, just send us the file and we should be able to fix them for you.

Where the fixes are quite minor and quick for us to resolve, then we will do this free of charge. In the case of more involved problems, then we will provide you with a quote for us to fix them for you.

Free File Fixing Software:

Mini Magics from Materialise is a free file viewing software for viewing errors.

Meshlabs is an open source processing and editing software.

Professional File Fixing Software:

These professional software programs provide advanced fixing functions.

Magics is the professional software from Materialise for file viewing and fixing errors. It is "a versatile, industry-leading data preparation and STL editor software for Additive Manufacturing that allows you to convert files to STL, repair errors, edit your design and prepare your build platform."

The professional version of Netfabb allows you to do more advanced fixing, allowing you to "Quickly prepare, optimize and validate your designs with a flexible set of editing tools that will help you create high precision 3D prints."