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STL File : the most common errors

STL File : the most common errors

Normal lines inverted, holes and multiple shells

In this article, we will discuss the most common errors found in STL files, which usually involve inverted normals, presence of holes, and multiple shells.

These errors often result from mistakes during part modeling or during the export and conversion process to the STL file format using CAD software. These defects need to be corrected in order for the part to be suitable for printing.

As highlighted in the previous post, the STL file, necessary for 3D printing a part, represents a three-dimensional geometry composed of triangles oriented in space.

Example of a STL file

Normal line inverted

Each triangle is described not only by the coordinates of its vertices, but also by the normal, which is a vector perpendicular to the plane on which the triangle is positioned, and its orientation defines the outer side. In some cases, the normal of these triangles can be inverted, mistakenly identifying an outer side as the inner side and vice versa. Such a situation can lead to errors during the printing process.

Example of a normal line inverted 

Example of a normal line corrected

Hole in the STL file

The second most common error encountered is the presence of holes, which can be caused by missing surfaces or misalignment between triangle vertices.

These holes need to be manually corrected if they are of considerable size, or automatically using specialized software if they are smaller. The presence of holes can compromise the quality and functionality of the printed part.

The presence of holes can compromise the quality and the realization of the part printing.

Holes in a STL file

STL file corrected

Shell Multiple

Lastly, we encounter the issue of multiple shells. A shell refers to a group of connected triangles. The presence of multiple shells in a part indicates the presence of separate groups of triangles. In this case, the inner shell overlaps with the outer shell.

Resolving this type of error is necessary to avoid anomalies during the slicing of the model into layers or incorrect surface generation, as well as to prevent printer jams. It is important that all shells are properly joined to achieve a coherent and functional printed part.

This situation can also occur when, in the design phase, the shapes that make up the CAD model are not properly integrated into the rest of the shell, but remain separate.

It is crucial to ensure that all components of the model are correctly integrated into the main shell to avoid printing issues and ensure the quality of the final product.

Example of Multiple shells

Example of Multiple shells

Multple shells fixed 

When we receive the files. stl from our customers, it frequently occurs the need to make changes and corrections before proceeding with the production.

STL correction requires specific skills and the use of dedicated software to repair imperfections and ensure that the part is ready for printing.

Our team is fully committed to making such corrections with the utmost precision and timeliness, in order to ensure that the printed parts reach high quality standards and fully meet customer expectations.

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The Prosilas Staff will respond promptly by sending a detailed estimate with costs and delivery times.

STL File : the most common errors

STL File : the most common errors

Normal lines inverted, holes and multiple shells In this article, we will discuss the most common errors found in STL files, which usually involve inverted normals, presence of holes, and multiple shells.These errors often result from mistakes during part modeling or...

What is an STL file?

What is an STL file?

It represents a three-dimensional geometry by means of a combination of triangles unfolding in three-dimensional space.

What is an STL file?

What is an STL file?

An Overview of the Three-Dimensional Representation for 3D Printing

Today, we delve into the analysis of the STL file extension and its crucial role in the realm of additive manufacturing. If you are interested in the world of 3D printing, you are likely already familiar with this extension and its unique characteristics.


Example of STL file

STL file

Essentially, the STL file represents a three-dimensional geometry through a combination of triangles arranged in three-dimensional space. This representation simplifies more or less complex surfaces, modeled using CAD software, into a series of planar triangles described by the Cartesian coordinates of their vertices.


The primary reason for the widespread use of the STL fileformat in the field of additive manufacturing lies in its ability to translate the language of CAD software, which is based on mathematical functions, into a format understandable by all 3D printing technologies on the market (SLS, SLA, FDM, etc.). This simplified format is based on a three-dimensional coordinate system, which represents a more accessible and immediate language for different printing technologies.

Export of  STL file

We often encounter the receipt of files with different extensions, such as .iges or .step, or even proprietary files from modeling software, each with specific characteristics. However, in order to materialize them through 3D printing, they need to be transformed into the STL file format. This conversion process simplifies the 3D models but may involve some modifications, such as approximating cylindrical or spherical parts and the presence of facets that do not accurately reflect the originally designed surfaces.

Example of 3D modelled file

Example of correctly exported file in STL with good resolution

Example of file exported in STL with incorrect resolution. Note the inside of the hole that has lost its initial sphericity.

STL file resolution

It is directly related to the number and size of the triangles that make up the model. A large number of triangles implies a higher resolution.

However, it is important to emphasise that a large file size does not necessarily mean significant advantages. Rather, it is preferable to adapt the size of the triangles to the printing resolution of the machine used. For example, our SLS machines operate with a resolution of about 5 hundredths of a millimetre. Therefore, it is vital to have a correctly adapted .STL file in order to guarantee optimum surface resolution.


Read more on Prosilas

What is an STL file?

What is an STL file?

It represents a three-dimensional geometry by means of a combination of triangles unfolding in three-dimensional space.

read more

Contact us

The Prosilas Staff will respond promptly by sending a detailed quote with costs and delivery times.

Lube Volley and Prosilas together to win, with the support of 3D printing

Lube Volley and Prosilas together to win, with the support of 3D printing

Lube Volley + Prosilas Case History

What Prosilas and Lube Volley have in common is not only their city of origin, Civitanova Marche, but also their shared pursuit of challenges and desire to succeed. For the esteemed Marche team, this translates into winning trophies and championships. Meanwhile, for Prosilas, it means constantly seeking innovative solutions to support the development of an increasingly demanding industrial market. The collaboration between the two companies was recently solidified through a sponsorship agreement, which prominently displays Prosilas’ name on the volleyball team’s uniforms. Additionally, they engage in a strong joint effort that connects sports achievements with the utilization of additive manufacturing.


Lube Volley, Prosilas-supported club is the  most successful in the 21st century


Champion of Italy 2022, Lube Volleyball is an acclaimed team, boasting  in its list of victories a World Club title, seven league titles (the last three won consecutively), two Champions Leagues, seven Italian Cups and four Italian Super Cups, three CEV Cups and one Challenge Cup. The team expresses a very high technical level of play, capable of always competing at the top: and when playing at high levels even small details can make a difference.

Lube Volley, the team

A tangible collaboration, thanks to 3D printing


When Enrico Diamantini and Ivan Zaytsev, two prominent athletes from the club, expressed their need for new hand protection devices during games, the relationship between Lube Volley and Prosilas evolved beyond a simple sponsorship. Prosilas immediately utilized its expertise in 3D printing to develop an innovative, customized, and tailored solution for both players.

We took the opportunity to get even closer to the world of medicine and sport, trying to develop a truly useful and professional application,’ says Vanna Menco, CEO Prosilas

Diamantini required an alternative to the temporary brace he had been using to support his injured right little finger, while Zaytsev needed a replacement for the medical tape he typically used to stabilize his fingers during high-impact phases of the game.

Ivan Zaytsev and Enrico Diamantini

The previous solutions had limitations in terms of materials, lacking of technical performance, reusability, and customization, which resulted in a sub-optimal playing experience. However, with the advent of 3D printing, Prosilas believed that they could overcome these limitations and produce custom-made and reusable devices with exceptional speed and precision.

For Diamantini, the old brace was rigid, bulky, and therefore uncomfortable. The negative impact on his ball touch led him to use it sporadically and only for the minimum required time. Similarly, Zaytsev sought a custom-made, reusable alternative that provided better sensitivity compared to traditional medical tape.

Through their collaboration with Prosilas, both athletes found the solution they were looking for, addressing their specific needs and improving their playing experience on the court.

Fast and successful product development

 The initial phase of the project focused on acquiring the 3D models of Diamantini and Zaytsev’s hands using the Gom Atos 5 3D scanner, which involved scanning plaster casts. Subsequently, the design phase commenced, incorporating reverse engineering techniques to accurately model customized designs. These designs were tailored to protect and immobilize the injured joint in one case, and provide comfortable support in the other. The devices underwent testing and, with valuable feedback from the athletes, were progressively refined to achieve the best possible results.

“The responsiveness of additive technology is truly remarkable. The initial contact with the players took place in October 2022, and after just five rounds of improvements, we were able to arrive at the final version of the devices for both players within a very short timeframe,” states the CEO of Prosilas.

3D scan of Ivan Zaystsev’s right hand

3D design through reverse engineering of protective devices

TPU protective devices being tested on the cast of Ivan Zaystsev’s right hand

TPU: a strategic choice


To create these customized and highly comfortable devices, Prosilas opted for BASF’s TPU Ultrasint 88a due to its flexibility and mechanical impact resistance. Thermoplastic polyurethane (TPU) is an elastic polymer known for its versatility and resilience. It can withstand shocks, abrasions, tears, chemical and weathering agents, and is impermeable to water and gases.

TPU is often considered the intersection between rubber and plastic, thanks to its physical characteristics, wide range of hardness options, and flexibility without the need for plasticizers.

For the initial test with Diamantini, three different TPU models were created using SLS (Selective Laser Sintering) technology, each with varying thicknesses of 1, 1.5, and 2 mm. TPU allows for slight variations in thickness, enabling flexibility in the final product.

For Zaytsev, an initial set of devices was produced with a consistent thickness of 2 mm to provide greater rigidity. Additionally, a lateral cut was made to improve the fit of the devices for him.

3D design through reverse engineering of protective devices

TPU protective devices for Enrico Diamantini in three different thicknesses: 1, 1.5 and 2 mm

Testing phase and results

“The results achieved through the utilization of additive technology are undeniably positive,” remarks Vanna Menco. “This is further corroborated by the outcomes of resistance tests conducted on the material by our supplier, BASF 3D Printing Solutions.”

 The testing phase was a critical step in the process. Collaborating with BASF, an effort was made to replicate a volleyball game in a laboratory setting. This involved evaluating the material’s chemical resistance, short and long-term durability, as well as color stability.

To assess the material’s mechanical stability, strength tests were conducted after 30 minutes, 7 days, and 14 days, with the parts immersed in synthetic sweat.

Tensile strength and elongation at break were measured at these intervals. Furthermore, a sudden impact test was performed to simulate crushing, and no significant changes were observed. The color measurement, which determined its stability over time, confirmed that there was no yellowing or noticeable alteration after 14 days. These results provide evidence of the material’s reliability and longevity.

TPU testing samples

Sudden impact test results

The remarkable durability and strength of the custom 3D-printed devices can be deduced from the absence of significant degradation observed during testing. This ensures the longevity of the product even under repeated stress and in special chemical conditions. Apart from the scientific findings, the enthusiastic feedback from the athletes themselves confirmed the positive results and the significant improvement in playability and game feel.

“I recommend the protection systems made by Prosilas to everyone. Because they are customized, they give maximum comfort in every technical gesture. It’s like not having them!”

says Enrico Diamantini, who used the device during his recovery from a dislocation.

Ivan Zaytsev, on the other hand, continues to use the customised devices on his hands. He says:

“Thanks to Prosilas, I immediately felt comfortable with hitting the ball, the four braces were  efficient and above all eco-friendly given the amount of tape they save me!


The combination of improved performance, stable feel, durable material, and complete customization results in an overall increase in comfort for athletes during competition, leading to an enhancement in playing performance.

Customization has become an essential trend in the world of ultra-competitive champions, and additive solutions go above and beyond by offering specific shapes and characteristics tailored to each individual athlete’s needs.


Working with BASF 3D Printing Solutions


BASF 3D Printing Solutions, operating under the Forward AM brand, is a division of BASF New Business GmbH that is specialized in advanced materials, system solutions, components, and services in the field of 3D printing. With a lean structure and an agile mindset akin to a start-up, BASF 3D Printing Solutions is well-equipped to cater to the diverse needs of various industries by offering innovative and customized services. The company works closely with other departments within BASF, research institutes, universities, start-ups, and industrial partners to serve customers in automotive, aerospace, consumer goods, and other product categories.

The partnership with BASF 3D Printing Solutions holds significant strategic importance for Prosilas, further solidified by the mutual respect between the two companies.

 “Prosilas brings extensive experience in printing our flexible TPU materials, ensuring the consistent delivery of superior quality parts,” explains Tobias Haefele, Product Manager Powder Bed Fusion. “We greatly appreciate their exceptional creativity,” he continues, “and their attitude to push the limits of the 3D printing market, paving the way for new applications, which align with our vision. With their specialist knowledge and established presence in sectors such as fashion, they have earned our trust as a reliable partner in consistently delivering exceptional products over the years. At BASF 3DPS, we are excited to continue our journey with Prosilas, forging a promising future for additive manufacturing.”

Prosilas, Quality goes through the metrology lab

Prosilas, Quality goes through the metrology lab


Metrology laboratory

There is also an efficient metrology lab among the many investments with which Prosilas celebrates its first twenty years in business. It was in fact 2003 when Giulio Menco, an experienced aeronautical engineer who realised the enormous potential of 3D printing applied to industry, started a rapid prototyping service using additive technology.

Then the baton was passed on to his daughter Vanna, the current CEO of Prosilas: her strong entrepreneurial skills, passion and determination have made the project grow to such an extent that the company has become one of the largest additive manufacturing centres in Europe, so much so that in 2022 the service became part of Prototal Industries, Europe’s largest polymer processing group, and obtained the important ISO 14001:2015 environmental certification.

This year the company is therefore celebrating its 20th anniversary with major investments: an expansion of the plant and workforce and a renewal of the ‘technology park’, both for quality control and production. Including, of course, a metrology laboratory.


Matteo Biancamano, Quality Manager, Roberto Nasini Senior Technician, Marco Soldini Plant Manager

Metrology at the service of quality control

In addition to acquiring new production devices, Prosilas has also chosen to invest in a metrology laboratory where precise and reliable measurements are made on the instruments and materials used, so that they conform to the standards required by the market and have certified quality. ‘The role of the metrology lab,’ says Matteo Biancamano, Quality Manager at Prosilas, ‘is to verify and control our internal production process. The components we produce are measured either by scanning with a GOM Atos5 scanner or through gauges that are regularly calibrated with planparallel blocks. The laboratory is also equipped with a calibrated pin set and a brand new Galdabini tensile machine. All measuring and calibration equipment is Accredia certified.”

scansione 3D

Instruments and analysis cycle in the laboratory: the scanner

But what actually happens in the metrology lab?

“Let’s start with the scanner,” explains the Quality Manager, “while the machine goes through its warm-up phase (about 40 minutes) and comes up to temperature, ready for scanning, the component to be analysed is placed on the rotary table and alignment marks are attached to it. Once the scanner is started, the component is brought into focus and the series of measurements and image acquisitions begin, leading to the dimensional checks, through the analysis and comparison of surfaces and the resulting dimensional reports.”

And that’s not all: the analysis and measurement cycle includes further steps. “During the pre-alignment phase,” says Biancamano, “the software recognises the geometries of the part and cross-references them with the 3D files. The best-fit phase, on the other hand, involves the analysis of specific zones for an even more accurate and specific dimensional investigation. Subsequently, the comparison and surface analysis allows any discrepancies to be identified.”

Instruments and analysis cycle in the laboratory: the tensile machine

“Lastly, we have a Galdabini tensile machine which, once we have inserted a few sections of the material we wish to measure, exerts a force over time until our sample breaks. Once this last test has been carried out, the software releases the graph of the entire measurement process, showing the trend of the force as a function of the component’s elongation. This tool is very useful to have more control over our production. For example,’ Biancamano concludes, ‘it is possible to check that the mechanical performance of our components is homogeneous throughout the entire production process, even considering the orientation of the component itself on the machine, so that we can then be able to advise the customer more precisely.”

The objectives of the laboratory

“Now, the objective of our metrology laboratory is to guarantee consistently high quality standards over time on all our production and to increase our experience, in order to be able to transfer it to our customers, for whom we want to be true production partners. For the future, however, the goal will be to implement and acquire more equipment to enable us to offer an even higher quality product. This is why more personnel will certainly be trained on the use of all the instrumentation in the laboratory,” concludes Matteo Biancamano.

Being a service and cosulting partner for Prosilas means providing customers with a sustainable, advanced and flexible way of managing production by offering the widest range of solutions, where quality is measured, guaranteed and certified.

Read more on Prosilas

What is an STL file?

What is an STL file?

It represents a three-dimensional geometry by means of a combination of triangles unfolding in three-dimensional space.

read more

Contact us

The Prosilas Staff will respond promptly by sending a detailed quote with costs and delivery times.

KTM chooses Prosilas 3D printing to ride in the wind

KTM chooses Prosilas 3D printing to ride in the wind

Ktm + Prosilas Case History

Passion for speed meets 3D printing innovation

Since the beginnings of 3D printing, one of the sectors that has most perceived and grasped its potential is undoubtedly racing and motorsport. The demand for parts and components with high mechanical performance, but in limited production runs and tight deadlines, make additive manufacturing the ideal choice for those who produce high performance cars and motorbikes.

This is well known by the Austrian company KTM, whose Aerodynamics and Factory Racing departments have persistently researched and developed revolutionary solutions, not only for the production of functional prototypes, but also for end-use components, to be used both in the wind tunnel and on the track.

A partner for 3D printing of carbon-filled nylon elements

It was precisely with a view to creating parts capable of exceptional performance, not only mechanical but also aerodynamic, that the collaboration between KTM and Prosilas was born. In particular, Prosilas’ role is to work alongside the Austrian giant as a partner for the 3D printing and finishing of parts in Polyamide PA2200 added with carbon fibre using SLS technology. A true additive manufacturing process in Nylon with carbon that, thanks to the printing parameters specifically studied by Prosilas technicians for the EOS P770 printer, has also been proposed for large format parts (680x370x540 mm chamber). Prosilas is the only company on the European scene that can offer this kind of 3D printing for objects and components of this size in PA 603 CF  material.

Aerodynamic appendix for the motorbike KTM RC16 MotoGP

Brad Binder, Red Bull KTM, MotoGP RC16 Circuit Ricardo Tormo

From simulations to the wind tunnel: what were KTM’s objectives when you chose Prosilas as your partner?

The desire was to identify and develop additive-moulded materials that could undergo post-processing to bring the surface finish up to the levels required for our aerodynamic needs,” says Daniel Marshall Team Leader Aerodynamics at KTM: “In particular, we needed to improve the correlation between simulations and subsequent testing, and then possibly produce parts that could cope with track tests and even race events. Thanks to the qualities of PA 603 CF and the surface finishes offered by Prosilas, we can now have parts that fully meet our requirements. We have been able to decisively improve the correlation between computational simulation and wind tunnel testing“.

Vanna Menco, CEO Prosilas, Noemi Rossi, Sales Manager Prosilas, Daniel Marshall Team Leader Aerodinamics KTm , Michele Paolinelli Sales Account Prosilas

From right to left: Vanna Menco, CEO Prosilas; Noemi Rossi, Sales Manager Prosilas; Daniel Marshall Team Leader Aerodinamics KTM; Michele Paolinelli Sales Account Prosilas @ KTM Factory Racing 

Brad Binder  & Jack Miller,  motorbike RC16 Red Bull KTM. MotoGP 2023

Constant comparison in the name of optimisation

Highly innovative results, therefore, achieved through an ongoing collaboration between KTM and Prosilas to combine aerodynamic and engineering expertise with that of additive manufacturing: “The choice of materials and surface and post-processing finishes was made in constant collaboration with Prosilas,” explains Daniel Marshall. “Thanks to this partnership, further progress was made in optimising the components in terms of weight, rigidity and waste reduction

What made KTM choose 3D printing over the traditional methods previously used?

“We decided to go for 3D printing for two very specific reasons: short lead times and minimal quantities,” concludes Daniel Marshall: “We usually produce test parts in one-offs, so traditional production processes are not applicable in terms of both cost and delivery time.

Additive technology allows finished parts in production timescales that are unthinkable for any other technology. For example, eight aerodynamic appendages for the tail of the KTM RC16 MotoGP motorbike were printed and finished within just four days of the order being placed. An astonishing result, which only reaffirms the now inseparable link between racing and motorsport and 3D printing.

A story, the one between Prosilas and the historic KTM, that once again confirms Prosilas’ commitment to being a winning ally to industrial production.

Appendice aerodinamica per la moto KTM RC16 MotoGP

Read more on Prosilas

What is an STL file?

What is an STL file?

It represents a three-dimensional geometry by means of a combination of triangles unfolding in three-dimensional space.

read more

Contact us

The Prosilas Staff will respond promptly by sending a detailed quote with costs and delivery times.

Eos P770 n° 5

Eos P770 n° 5

The fifth Eos P770 3D printer has arrived! 

In addition to improving production efficiency, it is the speed of the process that makes the difference.

The EOS P770 3D printer is a strategic solution that allows us to provide a better service: more optimized and innovative!

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