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How to cut STL models for 3D printing in Meshmixer

There are at least three cases where cutting objects into smaller components could be your best option:

  1. Your model is too big and does not fit inside the print volume.
  2. Your model does not have any suitable flat surface to serve as a base to be placed on the bed.
  3. You want to avoid using support material or at least decrease the amount of support material.

The first case is obvious. If it’s too big, there is no way of printing the model as one piece. Cases number 2 and 3 are a little bit trickier to recognize. Imagine you’re printing a perfect sphere. No matter which orientation you choose, only a tiny area will be in contact with the bed, and the print will inevitably fail. However, when you cut the sphere in half, you can easily place each hemisphere on the print bed and print it without problems. Such a simple cut can be made directly in Slic3r as explained in our Beginner’s guide for Slic3r Prusa Edition.


Printing sphere in one piece vs simple cut along the Z axis

However, a simple cut along the Z-axis is not always enough. Sometimes, you’ll want to cut along the X or Y axis, or even with an arbitrary positioned plane. For that, the simple cutting in Slic3r is not enough. A good option is to use Meshmixer, cutting model in it is fast and easy.

Simple plane cut in Meshmixer

We’ve been using Meshmixer in our previous tutorials, and we’ll continue to do so. It’s free, easy to use, and powerful software for editing and repairing 3D models. It’s available for both Windows and Mac (no Linux support though). Developed by Autodesk, it includes features like plane cuts, hollowing, adding custom supports and much more. In your typical workflow, it will fit as a step between creating/downloading model and slicing. You can download Meshmixer here.
  1. Select Edit – Plane Cut
  2. A plane will appear. You can move it around using the three-axis gizmo
  3. You can also define a plane by holding down the left mouse button and moving the mouse
  4. Select whether you want to keep both halves (slice) or just one (cut) from the Cut-type drop-down menu
  5. Select the hole filling method from the Fill-type drop-down menu.  The default usually works great. You can learn more about the various filling methods in Meshmixer documentation.
  6. Accept the cut. The model will still look like one piece.
  7. Select Edit – Separate Shells to split the model into two
  8. Select one of the newly created halves, and click Export from the menu on the left to generate an STL file. Repeat the process for the other half.


A plane cut of the Hulk

Advanced cut in Meshmixer

By default, Meshmixer cuts with an infinite plane. As a result, you might be accidentally cutting areas of your model that you wished to stay as one piece. This is most commonly a problem when cutting figures as illustrated in the image below.


Cut with an infinite plane vs a cut with dimension constrained plane

To prevent this behavior, we can specify a smaller area to be affected by the cut. Everything outside of this selection will ignore the plane cut and stay as one piece.

  1. Choose Select from the left menu. By default, a brush tool is selected.
  2. By holding down the left mouse button, you can paint over parts of the model to select them. Selected triangles turn orange.
  3. Alternatively, choose the lasso tool using the switch in the top left corner.
  4. By holding down the left mouse button, draw a curve/loop. Everything inside the loop will be selected. Unlike the brush tool, this will also select triangles on the other side of the model, that are not facing the camera.
  5. Once your selection is complete, a new menu will appear on the left side. Select Edit – Plane cut from the new menu. If you accidentally use the Edit – Plane cut from the main toolbar, your selection will be discarded.
  6. Proceed the same as with a simple cut. Only selected triangles (orange) will be affected by the cut.


A cut through selection (right arm). Note that the cut does not affect Hulk’s body, even though the plane intersects it

Adding aligning pins

When you finished printing individual parts, you’ll have to glue them together. This can get somewhat tricky and you’ll have to hold the pieces perfectly aligned as the glue cures. If the glue takes too long to cure, it’s difficult to keep the parts aligned the whole time and sometimes it’s impossible to use a clamp. And if it takes just a second (e.g., super-glue with an activator), you only have one shot and if you misalign the parts, it’s already too late to fix it. For this reason, it’s a very good idea to add some aligning pins. Doing this in Meshmixer is at the edge of its capabilities, but it’s doable. In a future tutorial, we’ll tackle the same problem with a more powerful, but also more complex software.

  1. Cut the model (follow the steps for simple or advanced plane cutting)
  2. Open the objects browser View – Show Objects Browser (CTRL+Shift+O)
  3. Hide one of the objects by clicking on the eye icon in the Objects Browser
  4. Select Meshmix, pick a primitive (a cylinder for example) and drag it to the plane of the model, created by the cut
  5. Position and scale the primitive, so that it can work as an aligning pin
    • You can move the primitive around by dragging the sphere gizmo in the middle of the primitive
    • You can scale the primitive by dragging the arrow shape next to the sphere gizmo
  6. In the Drop Solid menu on the left change Composition mode to Create New Object
  7. Hit Accept when you’re happy with the scale and position of the primitive
  8. Select the primitive and duplicate it by hitting Shift+C or by clicking on the duplicate icon in the Objects browser
    1. Repeat this two times so that you end up with 3 copies of the primitive
  9. Select the model (Hulk) and then the primitive (cylinder), then click Edit – Boolean Difference
  10. In the new window on the left, untick Auto-Reduce Result, tick Use Intersection Curves and decrease Target Edge Scale
  11. After you hit Accept, the primitive will disappear. Luckily, we made a copy of it in step 8
  12. Repeat the Boolean Difference with the other half of the model (steps 9-10)
  13. This consumed another copy of the primitive.
  14. Export both halves of the cut object and the last copy of the primitive one by one as STL
  15. When you’re preparing the G-code in a slicer, it’s a good idea to scale the primitive down a tiny bit to create clearance for the aligning pin


You can download Low Poly Hulk model by Tom Davis from MyMiniFactory.



3D Systems' High-Quality 3D Printed Appearance Models Provide Trade Show Support at Oil …

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Large-scale parts and machines are not always the easiest, or cheapest, objects to bring to a trade show or conference. But 2D photographs just don’t offer the same kind of experience as actually seeing the object for yourself, so sometimes the next best option is a scale or appearance model, which can offer support at trade shows, as well as provide design verification and allow for simulation tests.

3D Systems, and its On Demand Manufacturing service, has experience creating scale models and appearance models for companies, and recently worked with Netherlands-based Seatools to create seven distinct 3D printed appearance models of its multiple custom underwater technologies for an important conference.

Seatools designs, builds, and tests custom equipment to solve subsea challenges for its global customers, which include companies in the offshore oil and gas, aquaculture development, and offshore renewables industries. This spring, the company attended the world’s largest oil and gas industry event, the Offshore Technology Conference (OTC) in Houston, and needed a way to quickly and effectively showcase its custom offerings in a creative display so it could attract attention and new business.

The company determined that it would need high-quality, detailed models that could be manufactured quickly, would reflect the company’s high standards, and be durable enough to survive a trip across the ocean.

So Seatools turned to 3D Systems’s On Demand Manufacturing services, which offers support across the entire product development lifecycle with services like fast 3D printed parts, low volume manufacturing, and advanced prototyping. Seatools identified seven different models that would best showcase its custom underwater technologies in a unique subsea landscape, and determined that 3D printing technology would be more efficient and less expensive than conventionally manufactured scale models.

“It was very important to me that the models arrive in Houston in one piece. We are a company that sells high-end equipment with high quality, so if we were to show broken models on the show floor, it would not be in line with the quality we sell to our customers,” explained Johan Sol, a member of Seatools’ supervisory board and marketing and business development office.

“The 3D models had to be transported by freight, and we knew from other scale equipment models in the past that they endure a lot of shock loads.”

Seatools decided on SLS 3D printing technology, which offers advantages such as visual appeal and durability, and is used often for functional applications, like living hinges, which was useful for this particular project. After speaking with 3D Systems’ On Demand Manufacturing experts, the company decided to go with strong nylon 3D prints, made with 3D Systems’ DuraForm PA material and produced on its sPro 230 SLS system.

Seatools relied on 3D Systems throughout the entire process, from CAD file optimization and 3D printing to painting and assembly, so it was able to focus on getting ready for the trade show.

3D Systems made the decision to engineer separate components for each of the models, in order to deliver accurate 3D appearance models that met with Seatools’ high quality standards. Once the scale models were 3D printed, 3D Systems’ experts painted and pieced them together in a final assembly that precisely met the project specifications and were, according to Sol, “striking and effective.”

Not only did the 3D printed, diversified scale equipment models survive the trip, they accurately represented Seatools’ full-sized machinery. The company was able to include more high-quality details in the 3D printed models than it could have with conventional manufacturing techniques, thanks to the material properties of SLS 3D printing and its ability to create strong but thin walls.

According to 3D Systems, the 3D printed appearance models “played an instrumental role” in Seatools’ display – they definitely showcased the same level of care and quality that the company offers its customers, and helped show off its diverse offerings as well. Sol says companies only have a few seconds to catch the attention of trade show attendees, and the 3D printed models paired with the subsea landscape attracted crowds to Seatools’ OTC booth, and also allowed the company’s sales team to make its pitch more interactive.

Sol said, “Our team could use the subsea world to reference the various models and tell a story about the company while showing the diverse capabilities of Seatools. The subsea landscape was really an eye-catcher. It drew a crowd and helped introduce us to new companies to start building new relationships.”

Discuss this story and other 3D printing topics at 3DPrintBoard.com or share your thoughts in the Facebook comments below.

[Source/Images: 3D Systems]

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3D printed models of cardiac conduction system could help doctors tackle troublesome heart rhythms

Aug 4, 2017 | By Benedict

Scientists from a number of British and Danish universities have developed a new way to visualize the cardiac conduction system—the process that makes our hearts beat—in 3D. The study, which enables the 3D printing of heart models, could aid research into heart conditions.

Understanding the human heart is a critical area of medical research. By getting to know how the organ behaves, doctors can become better prepared to help us—potentially saving our lives—when the big red ticker goes awry.

New research demonstrates a way of visually representing in 3D the cardiac conduction system, the cells that allow our hearts to beat by generating and distributing a wave of electrical activity that stimulates the heart muscle to contract.

The study, titled “High resolution 3-Dimensional imaging of the human cardiac conduction system from microanatomy to mathematical modelling,” was carried out by scientists at the UK’s Liverpool John Moores University (LJMU), The University of Manchester, and Newcastle University, as well as Denmark’s Aarhus University.

Published in Scientific Reports, the research claims to offer a “much more accurate” framework than ever before, and could ultimately help doctors tackle unusual and dangerous heart rhythms. Atrial fibrillation, one such rhythm, affects 1.4 million people in the UK.

The new 3D data system is able to show exactly where cardiac conduction system is in a normal heart—that happens to be right up close to the aortic valve—but could also be used to gather information about less stable hearts.

“The 3D data makes it much easier to understand the complex relationships between the cardiac conduction system and the rest of the heart,” explains LJMU’s Professor Jonathan Jarvis. “We also use the data to make 3D printed models that are really useful in our discussions with heart doctors, other researchers, and patients with heart problems.”

The researchers say the 3D system could help cardiologists identify the location of the cardiac conduction system in abnormal hearts. This will help surgeons carry out tricky procedures to repair the organ without damaging it.

To obtain 3D data about hearts, post-mortem organs were in a solution of iodine, which makes them able to absorb X-rays. X-rays are then used to collect detailed 3D images on the hearts, identifying the boundaries between single heart cells and detecting the direction in which they are arranged.

The data gathered from these X-rays can be turned into an accurate digital version of the scanned heart, and can even be transformed into a 3D printable model to help surgeons prepare for procedures.

“When the data is presented as 3D images or 3D printed models, it will inform discussions between medical teams and their patients, and aid the education of medical and surgical trainees,” the researchers explain in their paper.

Micro-CT scanning was carried out using the Nikon Metris XTEK 320 kV Custom Bay and Nikon XTEK XTH 225 kV systems at the Manchester X-Ray Imaging Facility at the University of Manchester.

“This is just the beginning,” claims Dr Halina Dobrzynski of the University of Manchester. “The British Heart Foundation is supporting my group to visualize this system in 3D from aged and failing hearts. With my research assistant Andrew Atkinson, and working with Professor Jonathan Jarvis, Robert Stephenson, and others, we will produce families of data from aged and failing hearts in 3D.”

Posted in 3D Printing Application

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San Diego researchers cut operation times by 25% with 3D printed hip models

Aug 3, 2017 | By Benedict

Bioengineers from the University of California San Diego and physicians from Rady Children’s Hospital are using 3D printed models to improve surgeries for slipped capital femoral epiphysis, the most common hip disorder found in children ages 9 to 16. Use of models cut surgery time by about 25%.

3D printed hip models helped San Diego surgeons cut operation times by around 25 percent

We see 3D printed medical models so frequently these days, it can be easy to accept their existence without questioning them.

But have you ever wondered just how useful such models can be—in numerical terms? While it makes total sense that a 3D printed model could improve a surgeon’s performance by allowing him or her to practice, sometimes it’s hard to gauge just how much improvement there really is.

That’s what makes a recent study at the University of California San Diego and San Diego’s Rady Children’s Hospital so important.

In the study, researchers created 3D printed models of patient hip joints, to allow surgeons to practice their procedure before doing the real thing.

But they also used a control group, letting a few surgeons perform the procedure without a 3D printed aid to see exactly how much difference the 3D printed models were making.

The study was published in a recent issue of the Journal of Children’s Orthopaedics.

In the study, Dr. Vidyadhar Upasani, pediatric orthopedic surgeon at Rady Children’s and UC San Diego and the paper’s senior author, operated on 10 young patients with slipped capital femoral epiphysis, a common hip disorder that affects about 11 in 100,000 children in the United States every year.

Five of Upasani’s operations were assisted with 3D printed hip models; five were not. Two other surgeons also operated on different groups of five patients, without using 3D printed models.

Excitingly, the results of the study showed 3D printing in a positive light. In the group where Upasani used 3D printed models, surgeries were 38-45 minutes shorter compared with the two control groups.

Student Jason Caffrey helped develop the 3D printed models

And according to the study’s researchers, these time savings would translate into at least $2,700 in savings per surgery.

Given that the kind of 3D printer required for the models would only cost around $2,200, such equipment clearly represents a solid investment—so much so, in fact, that Rady Children’s orthopedics department has already acquired its own.

“Being able to practice on these 3D models is crucial,” Upasani concluded. “It’s now hard to plan surgeries without them.”

To make the 3D printed models, two UC San Diego students, Jason Caffrey and Lillia Cherkasskiy, teamed up with Upasani, bioengineering professor Robert Sah, and their colleagues. They took CT scans of each patient’s pelvis, and used this data to make a computerized model of the bone and growth plate for 3D printing.

Printing took between four and 10 hours for each 3D printed hip model.

When completed, the 3D printed models allowed Upasani to visualize in 3D how the growth plate of each patient was deformed. This allowed him to familiarize himself with the patient’s physiology without using radiation-giving X-rays.

Although this study only focused on one kind of procedure, the speed improvement of 25 percent will be music to the ears of medical 3D printing specialists, and may encourage more hospitals to adopt additive technology.

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