May 12, 2016 | By Gambody Team

Gambody, during its 3 years of experience in the design and sale of 3D models, noticed that one of the most frequent problems 3D printing enthusiasts face when sending an STL file to print is that the model fails to print properly. That is, either the model falls apart or it prints with gaps and holes. As a customer who buys STL or OBJ files that are advertised as being error-free and optimized for 3D printing, this experience can be frustrating and can lead to losing trust in a certain 3D design company.

As a 3D design marketplace, these types of questions are inevitable. That’s why we decided to write a detailed article about these problems to clarify where the 3D design process fails to printing, so that, in the future, you can easily avoid them.

This article is written for those who have faced difficulties when printing complex 3D models. To make everything as clear and as easily digestible as possible, we will take this Lara Croft 3D model as an example. This model represents a fictional character from the Tomb Raider video game. After completing the work on its 3D design, the model looks as shown in the picture below.

Logically, the model consists of the head, trunk, upper limbs, and lower limbs. Often, the 3D printer fails to link all these parts together (this applies only for static models) so that the model falls apart or prints with holes and gaps.

Creating watertight objects

Graphically, the Lara Croft 3D printable model is made up of more outer shell elements that fulfil the function of generating the detailing. However, we can’t see the elements that make up the inner shell of the model, that intersect with the outer shell elements, like the elements that create the trunk and clothing of the model.

To distinguish between the trunk and the clothing of the 3D model, we colored them differently.

We will base our analysis on the 2 parts, the trunk and the clothing (graphically, these two parts represent 2 different objects).

As seen, the objects are watertight; there are no holes or gaps in them. This is the way the modeling of 3D designs for 3D printing is done to get clean printing results. There should be no empty spaces between two objects, if the planes/faces of the objects intersect.

As an example, we will take an object built from 2 primitive elements:

When intersecting 2 separate primitives, we see that only a part of the blue primitive is seen with the naked eye, while the other part is “built into” the red primitive.

This is a correct way to design a 3D model for printing. We do not necessarily need to use the “merge” feature to make a model for printing.

Preparing and checking the STL file for 3D printing

What you need to do next is to convert the object built from 2 intersected primitives into an STL file. Check it for errors in Netfabb (you can download Netfabb for free from the Internet).

If the object is accurately modeled, Netfabb generates the “repaired 100%” message. This means that the object passed the test and there are no errors, so we can continue with our work.

Save the repaired file and open it in an STL file G-CODE generator (manipulations done on X, Y, Z axes read by the 3D printer). Every 3D printer manufacturer provides certain software for this conversion. You can find the software and user guides on the 3D printers’ manufacturer’s official sites. We will use CURA 15.06 from Ultimaker2.

When we import the 100% repaired model in CURA 15.06, it will look as follows:

After having imported the model in CURA 15.06 and rip cut the model to see the layer pattern, we can see that the model consists of several separate parts. The rip cut enables us to see that the blue-colored primitive we intersected with the second primitive divided our model into 3 separate objects, with no joining points among them. This causes the printing of the 3D model to fail, i.e. the model prints in two separate objects that fall apart.

Correct software configuration is the key to quality 3D printing

To avoid this type of problem, it is required to enter correct setup values in CURA 15.06 software, so that the model will print as a whole.

CURA, as any other software, supports settings that enable the printing of the 3D model that we converted into an STL file as a whole, and not as the separate objects it consists of.

If we enter 0.00mm value for the setting, the software will generate 3 separate objects and the printer will print 3 separate parts. If we enter 0.04mm value, the software generates the model as watertight, with no gaps or holes in the model (the bigger the value, the thicker the layers, which we highly recommend).

This feature goes by different names from software to software so we advise to check the user guidelines and manuals made available on the official website of the 3D printer manufacturers.

We made this test on Lara Croft 3D model.

As seen in the picture above, the clothing object separated the upper limb of the character from the trunk.

When entering the setting we talked about above, the software generates a watertight and error-free model.

Of course, certain softwares have default settings, which can potentially simplify this process for you as you will not have to search for the feature to enter correct settings values. If however, the feature is not set by default, it will take only a couple of minutes to enter the correct setting values, which will save both printing time and material in the end.

Gambody prides itself on providing correct and tested printing recommendations for all 3D models available on its marketplace. Use them when sending a model to your 3D printer and enjoy a detailed and accurate printing result. It was using these tips and correct settings that we were able to successfully print this Lara Croft 3D model.

Conclusion

We hope this article will shed light on some common issues that users face when printing STL files. Spending extra time to make sure that the object is correctly model and the printing software is correctly configured will result in printing an accurate 3D model, without gaps and holes, with high outer shell detailing.

3ders.org's update (May 12nd, 2016 5:30pm CET):

One of our readers, named Xeno, has brought a point to our attention regarding the recommended settings listed in the article. He explains that using Horizontal Expansion in his Cura software expands the object rather than simply connecting the parts, which could make for serious size problems if your parts are meant to fit into each other.

After consulting with the Gambody team, it has become apparent that this problem is related to the Cura software version being used. They offer the following response:

"[Xeno] is right, only when referring to the older version of the software, and namely Cura 15.04. Our recommendations, however, are based on the newer version - Cura 15.06 and our entire article aims at offering solutions to the problems faced by those who use the latest version of Cura software.

The menus and the software differ slightly. For Cura 15.06 we use Horizontal Expansion - 0.04mm which applies only if Layer Height - 0.1mm. Otherwise, the model changes at printing (gets thicker). If we enter a smaller value than 0.04mm, the model will be printed with holes and gaps. If we enter a bigger value than 0.04mm the model loses its original shape.

Any software has its own settings. Some have configurations similar to those we are referring to; some have setting parameters that are similar to those the user refers to, and some are differently built…If you are using an older version than Cura 15.06 you need to apply Expert mode, Fix horrible and combine a or b setting."

Posted in 3D Design

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