You'll find that modeling for 3D printing imposes requirements on your design that you didn't have when designing for print or video. As your designs will be turned into real, physical objects, you'll have to make sure that every part of them will have enough volume and strength to be printable.

Our website runs an exhaustive number of checks on each model that you upload to assure that we'll be able to print (and ship!) the model to you without breaking it. Your design will need to pass all these tests before we'll add it to your gallery.

As these tests can fail because of a number of reasons, it can be hard to figure out what's wrong with your work. We wrote this tutorial to help you with that.

Shapeways | Your model will take longer to process

"We found some problems in your model 'xyz.stl' that we may be able to fix for you. Depending on the complexity of the design, this extra correction can take up to a few hours. When we're done, you will receive another email notification."

Explanation: This is an automated message to inform you that your model is going into the 'correction path' - a piece of software that will run some more time-consuming checks and which will attempt a a number of automated fixes. When it's ready you will receive a second notification mail with the result.

Please note that currently all STL files are handled in the 'correction path', so don't worry when you get this message after uploading an STL file.

Shapeways | There's a problem with your new model

"Based upon the size, volume and wallthickness of your model there is no printer available which is able to print your model."

Explanation: Your model is either too large or too small to be printed by our printers (or contains parts that are too small/thin to print without breaking). We check to make sure that we have at least one printer that can print your model - the largest print size currently being 35x40x40cm. The check is quite clever: it will reorient your model to see if it'll fit in a printer.

Two additional checks look at the minimum size of your object 0.5x0.5x0.5cm - we'd have a hard time finding anything smaller than that!), and at the 'minimum wallthickness'. To understand what this means, look at the 2D example below. There are several dimensions to the object, but the one that determines the finest object part or even the object's strength is where the object is at its thinnest (or d=1 in the example):


How to fix this: If you just uploaded an STL file, check the information on STL under 'What kind of file did you upload?'. Otherwise, please see 'fixing your file' below.

Shapeways | There's a problem with your new model

"Only manifold objects can be printed. Please investigate the manifoldness of your object and fix any open edges."

Explanation:  Due to the nature of the 3D printing process, all models need to be closed, manifold objects. Manifold means that each edge in your model is shared by exactly two faces - not more and not less. Manifold objects are always closed.

How to fix this: Please see 'fixing your file' below (we show some examples of non-manifold issues there).

Shapeways | There's a problem with your new model

"The model could not be validated."

Explanation: our importer could not read your file.

How to fix this:

• First, check to see if the file is not corrupt by loading it back into your own 3D application.
• For STL files: we've found that in some cases the supplied STL file is valid but you can still get an error. Try loading the file into MeshLab (free Open Source software) and exporting as STL again. Usually, this will result in a much smaller file (faster upload!) that our importer can handle.

If you keep getting this warning, try exporting your design in another file format and upload it again.

STL

STL files don't have a default unit. Depending on the software that you used to create it, its unit could be meters, inches or millimeters. You can select the required unit in our upload form once you've selected your STL file (these options will only appear after you've selected the file!):


X3D

Our servers interpret the default unit of X3D files as 1m. For most 3D applications, this means that you will have to scale down your model before uploading.

Collada

Collada files support multiple unit types, so select the right one before exporting. If your 3D application does not allow you to select a unit, we will interpret the results in meters - in this case you will most likely have to scale down your model before uploading.

VRML2/97

VRML files have a default unit of meters. In practice this means that you often have to scale down your model before exporting it to VRML2/97.
If you get an "invalid fileformat" error after uploading your VRML file then most likely you have tried to upload a VRML1.0 file. Unfortunately we do not support VRML1.0.
VRML files have the extension WRL.

Fixing a file is not always straightforward, but here are a few tricks that I picked up over the last few weeks:

1. Make sure that all the face normals are pointing outward. If your 3D application supports 'single-sided' rendering in the real-time view, turn it on. Faces with incorrect normals will show up as holes or black areas in your mesh.

2. Remove any modifiers and smoothing groups - we discard them and use only the mesh data. If you can, apply them to the mesh and save the result.

3. Make sure the mesh is completely manifold. Manifoldness is a mathematical concept, and in our case it means: each edge should be used by exactly two faces (not more, not less). I'll illustrate the concept of manifoldness by giving a few examples of objects that are not manifold.

Here's an example of a non-manifold object that would be rejected by our server- there's a hole in the mesh, and the highlighted edges around it are only used by one face each (instead of two):


The following two cubes share an edge - this edge is used by four faces. The problem here is that the point where the two objects meet is infinitely thin - we could never print and ship it without breaking the model.


This example is not so obvious: the cube has an additional internal face. You might not even notice it while you're working on your design, but as its edges are only used by one face, it's non-manifold.


4. Make sure the mesh is watertight. Actually, manifoldness already implies watertightness but I though I would mention it again. Imagine filling up your model with water - would there be any holes where the water could leak out?

5. If your tool doesn't offer a manifold or watertightness check, you can use Blender (also see this videotutorial on manifoldness checking ). Blender has a built-in non-manifold detection script. Here's how to use it:

1. Import your model.
2. Select the mesh and enter editmode by pressing TAB.
3. (STL Files only): Select all vertices (AKEY), and unify the  by pressing WKEY and selecting 'Remove Doubles'.
4. Make sure all vertices are deselected (press AKEY once or twice).
5. While still in editmode, press CTRL-ALT-SHIFT-M (try THAT with one hand! ;-).
6. Non-manifold edges will be selected. The information bar at the top of the screen will show the number of non-manifold edges. For example: 'Ed: 1-23', meaning 1 edge selected of 23:
   
   
   

6. If you're convinced your model is valid but it still generates errors, try scaling it down by a factor of 10 or even 100 and upload again.

After uploading we generate a 3D preview of your design. We use a smooth shading algorithm to light the model and this can sometimes lead to strange results, especially for models with large flat surfaces or sharp edges.

As this is just a preview, it does not affect the printed result! We're sending your geometry to our printers and we don't apply any smoothing to it.

Here's an example:

View in 3D application	Shapeways preview