INTRODUCTION TO 3D PRINTING FOR ARCHITECTURE, ENGINEERING & CONSTRUCTION (AEC)

Introduction to 3D Printing for Architecture Designers, engineers and construction professionals, like their peers in product design, have discovered the benefits of 3D (three-dimensional) printing to help them communicate more effectively, shorten project timelines, and gain faster approvals from project stakeholders. Applications for 3D printing in AEC (Architecture Engineering & Construction) include site plans, massing models, detailed design concepts, engineering analysis results, MEP system models, structural designs, 4D color-coded construction, and traditional presentation models. This document will aid architects, designers and 3D modelers in the preparation of watertight, solid AEC models for printing on 3D Systems’ (ZPrinter series) 3D printers. Thinking in 3D The ability to think in 3D is your greatest asset. Having a basic understanding of 3D space and its conventions as seen in modern 3D software is paramount. There are great benefits to creating in 3D; you are no longer limited by the ability to picture the projections of 3D ideas onto a 2D drawing plane. Features that were once confusing in a 2D elevation view are now instantaneously comprehended simply by rotating the object as if it were in your hand. Architecture CAD / 3D Modeling / BIM Software For many designers the design stage begins and ends in two-dimensions (2D). However, to create 3D printable models, the designer (or 3D modeler) will need to reconstruct the original 2D design as a 3D model using CAD / 3D modeling software. Designers already familiar with 3D modeling are one step closer to producing beautifully printed monochrome and color 3D models. There are many types of CAD / 3D modeling software applications on the market today. Since selecting an “ideal” application is based on the types of 3D models that you will wish to create for 3D printing, it is recommended that you fully investigate the features for each of (but not limited to) the popular applications listed below to determine which application best meets your creative and budget needs. In addition, taking advantage of the trial versions is a great way to become familiar with the user interface and determine if a certain product is right for you.

Revit formZ Bentley BIM software Lightwave Autodesk AutoCAD software family Maya SolidWorks 3ds Max Catia 5 Cinema 4D ProE Bonzai 3D Rhino ArchiCAD Inventor SketchUp Pro

Since many 3D modeling software applications have the ability to import industry standard 2D geometry (DXF, DWG, EPS, etc.), migration of 2D assets into a 3D modeling program is possible. Supported File Formats

3D Systems’ ZPrinters Support the Following File Formats

ZBD (ZPrinter ZPrint build file format) ZPR (ZPrinter ZEdit & ZEdit Pro file format) VRML (.WRL) (supports color and texture map import) 3DS (.3DS) (supports color and texture map import) STL (does not support color or texture map import) PLY (supports color import) FBX (supports geometry only, no color or texture maps)

Planning for 3D Printing The translation from the CAD / 3D modeling application format, to a supported file format (listed above), may leave a few errors in your model file, and the integrity of such a file should be checked using specialized file repair software before you print your 3D model file. In most cases, small errors can be corrected automatically, but larger errors may require manual repair by an specialist or 3D modeler. ZEdit Pro (offered with a 3D Systems’ ZPrinter) and Materialise’ MagicsRP are two great repair utilities that can be very handy tools for addressing such errors. Decide on a Scale and Print Size for your 3D Model When creating your 3D model, a great place to start is to decide on a scale that you will construct in. As long as you plan ahead and keep your scale factor and smallest printable feature (SPF) in mind there is no reason not to model at 1:1 scale. Modeling at 1:1 scale will allow you to use your knowledge of common sizes for doors, windows, ceiling heights, etc. In AEC, unless you plan to print a full-scale section (like a structural node or window frame section), model scale needs to be considered. Since 3D printable AEC models can be anywhere from 1:1 to 1:2000 (like a site plan), one must think about the implications of scaling such a model down to an intended printable size. Since a ZPrinter build area can vary in size, depending on which ZPrinter you will be using, determining the intended print size is key to producing great results. The intended print size will help determine the level of detail you should build to, your tolerances, and support/strength concerns. It will also help you determine whether or not you want to print your 3D model at a scale to fit within the size constraints of the ZPrinter build area, or print larger, individual, split sections separately, and assemble them later.

What is a 3D Shell? Regardless of the CAD or 3D modeling application that you use, modeling a 3D architecture model will produce what are called, “shells” (aka nodes, components, parts). A 3D shell can be simple geometry such as a door, a door knob, a door frame, a window pane, a window mullion, a floor, a wall, a stair case, a railing post, a railing, a roof, and any such ornamental 3D geometry which contributes to the overall glory of the intended 3D architecture model. An overall architecture model can often consist of dozens, hundreds, or even thousands of shells. Since each modeler models differently, no two models will contain the same number of shells. Being aware of the overall shell count can be very important for larger 3D architecture models.

3D door model A total of seven shells make up this 3D door model

Creating Your 3D Model In order to successfully model and print a 3D AEC model, the following topics need to be considered:

Creating/Modeling Watertight, Solid Shells Eliminating Holes (or Gaps) in your Shells Geometry Topology and Polygon/Facet Count Intersecting Shells Inverted Normals Avoid Coplanar (Overlapping) Surfaces Avoid Floating Shells / Geometry Smallest Printable Feature (SPF) – Minimum Feature Sizes Strength and Support Hollowing your Model Managing Shells Removing Unnecessary / Non Essential Geometry Recommended Work Flow Repairing your 3D Model Alternatives to Repairing your 3D Model

Creating/Modeling Watertight, Solid Shells Whether you use 2D drawings, splines, mesh modeling techniques or a dedicated AEC 3D modeling application to create 3D models, 3D printers require watertight, solid geometry as input. In order to successfully print a 3D model, all shells must be complete watertight solids. What is a watertight, solid shell? Let’s take a look at a simple six-sided cube (primitive), as shown below. In order for this simple cube to be a watertight, solid shell, all six sides/surfaces must be modeled, thus producing a shell that will “hold water” internally. If we remove (or fail to model) one of the sides, the result will be an open shell with a hole. With water now able to escape, the resulting geometry will not be a watertight, solid shell, and will not print correctly. As such, any geometry that has holes (or gaps) will not print correctly. In addition, since flat open surfaces (with zero thickness) (shown below) are also open shells, such geometry needs to be thickened into a watertight, solid shell in order to print correctly.

CORRECT SHELL Six-sided, watertight,

solid cube/shell

INCORRECT SHELL Open shell with

hole on top

If water can escape, it is not a watertight, solid shell

INCORRECT SHELLS

Flat open shells with zero thickness CORRECT SHELLS

Thickened, watertight, solid shells

Eliminating Holes (or Gaps) in your Shells One of the most common errors in a 3D model file is non-compliance with the vertex-to-vertex rule. Correct specifications require that all adjacent triangles share two common vertices. Non compliance can often result in hole/gap errors.

Problem vertex/point

Although file repair applications like ZEdit Pro can easily repair a simple gap error shell like the example below, understanding how to manually repair an error shell can be very beneficial.

Non compliant

vertex-to-vertex shell

Gap error (red) as shown in ZEdit Pro

Easiest solution is to delete the top three triangles/polygons…

…and “cap” / fill the hole

Another option is to combine/merge the two orange triangles into one triangle/polygon. When editing models such as this to make compliant, be sure to delete any floating unused points (like the left-over, unused, center point circled in yellow). Unused, floating points can cause gap errors.

A final option would be to delete the green triangle/polygon and manually construct 2 three-point polygons to close the hole.

When converting a file (or translating) from one file format to another, the end result can be a new file with missing and/or distorted geometry. Such missing/distorted geometry results in holes/gaps. In some cases the amount of missing, distorted and even overlapping geometry can be so extreme, that it can create exorbitant or impossible repair times. Manually identifying and repairing such missing geometry / holes is often challenging, especially when guess work (determining how the model is supposed to look) becomes a factor. Below is an example model containing many errors (as indicated by red).

In addition, if a model, like the one illustrated, has too few shells to work with, repairing such a model, using repair software like ZEdit Pro, can only be achieved on a surface by surface basis – a time consuming process. This particular model has only 96 shells, and the majority of the geometry is contained within one single shell. Keeping such details in mind when creating your 3D models will help minimize these types of problematic geometry.

Since models such as this one can be a challenge for file repair applications like ZEdit Pro and Magics, it is often best to address such models in the original CAD / 3D modeling application.

Geometry Topology and Polygon/Facet Count The key to producing great 3D printable models is to pay particular attention to your geometry topology and overall polygon count. Try to keep your geometry clean and your polygon count low. For example, our six-sided cube has six, 4-point polygons/surfaces (below left). It is an ideal 3D cube model. Its topology, once converted to one of the supported file formats (ex: VRML), will represent an ideal 3D printable cube (below right). Please note that as a result of the conversion/translation to VRML, we now have a cube with 12 triangles/polygons – a higher “triangulated” polygon count.

If we subdivide the cube several times (below left), we still maintain our cube geometry, but the topology and increased polygon count (384 polygons) has changed unnecessarily. Converting to VRML will result in an even higher polygon count (768 polygons). Same cube geometry as above, but with unnecessarily higher polygon counts. Unless you have good reason to increase the polygon count, keep it lean and simple. This will help avoid potential gaps and unnecessarily large model files.

Another example is that of a simple 1-inch diameter sphere (primitive). We could certainly model a sphere with 10,000 polygons to produce a smooth 3D printed result. However, we could just as easily create a sphere with 2,500 polygons (or less) and produce the same smooth 3D printed result. If we model our sphere with too few polygons, we can end up with a faceted printed sphere.

10,000 polygons 2,500 polygons 144 polygons

The scale of your sphere, or curved surfaces, will dictate how many polygons will be required to produce a smooth end result. The goal is to model your objects so that the individual polygon faces (or facets) are sufficiently small enough to avoid a “faceted look” when printed. There is no rule of thumb to determine the ideal polygon count. However, with a little experience, your knowledge of how to best prepare 3D models for 3D printing will grow very quickly. Since each 3D modeling application is different, options for increasing (or decreasing via decimation) the object’s polygon count (or density) can vary. If your object is a parametric object, you can change it parametrically. If your object is a mesh object (with no parametric history), using your modelers tessellate or subdivision features can help generate smoother, denser meshes. Remember: When converting your 3D model file to a supported ZPrinter 3D file format such as ZPR, VRML, 3DS, STL or PLY, your 3D model will be “triangulated”, thus increasing the polygon count. Intersecting Shells On a ZPrinter, 3D AEC models can have intersecting shells, as long as each shell is a watertight, solid shell. Let’s take a look at a fence model.

Our fence model consists of many shells Remember: depending on the intended print scale of the fence model, the thickening of

select shells (shown above) may be required

Let’s zoom into the corner post shell of our original fence…

…and hide one of its sides for a better look inside the shell. As long as each shell is a watertight,

solid shell, shells can intersect

A close-up better shows us these acceptable intersecting shells

Inverted Normals Supported 3D model files (ZPR, STL, VRML, 3DS & PLY) consist of triangles (or polygons). Each triangle/polygon has three points and a “normal” (or surface normal) direction. The “normal” is an invisible line which is perpendicular to the surface of the triangle/polygon. When creating your 3D AEC model, all normals should face outward (toward the outside of the part/shell), as shown below. Correct normal direction allows the printer to correctly add material. Incorrect normal direction suppresses material. All modern 3D packages offer tools for correcting normals manually as well as automatically.

CORRECT NORMALS DIRECTION Normals facing outward

INCORRECT NORMALS DIRECTION Normals facing inward

Although ZPrint can be forgiving of certain inverted normals, all inverted normals (often shown as a darker color surface in ZPrint) should be corrected prior to printing. Failing to correct inverted normals can often result in unsatisfactory 3D prints. With the aid of ZEdit Pro, normals can be corrected for optimal output.

White cube model with darker polygons could

indicate inverted normals

ZPrint’s 2D mode shows suppressed material (white areas indicate that no binder will be jetted and the layer will

not print) and confirms inverted normals

Correcting the normals in ZEdit Pro yields black (indicating that the layer

will print)

Avoid Co-Planar (overlapping) Surfaces for Non-Monochrome Models Co-planar surfaces can often cause unpredictable and unacceptable print results and should be avoided when you wish to print colored and/or textured 3D AEC models. Let’s take a look at an example of two wall shells, as shown below.

If we take two wall shells (top left) and slide them together to create, say, a corner of a house or building (top right), we get two overlapping, outside corner surfaces where the two walls meet. If our goal is to print a monochrome model, like above, where each of the shells surfaces is the same color, then the overlapping surfaces will not present a problem. However, if we wish to print a colored and/or textured model, with only the outside surfaces colored and/or /textured, we can clearly see in the below left and middle images, that the overlapping (competing) surfaces can create both unpredictable and unacceptable results; the corners are far from ideal. In fact, if we were to rotate these combined shells in our 3D modeling application’s perspective workspace window (or within both ZPrint and ZEdit Pro), we would clearly see the corner surfaces flicker as the two surfaces compete against one another in the open GL window. Modeling a colored and/or textured AEC model correctly (without overlapping surfaces), will allow you to print a highly desired 3D model, as illustrated in the image on the below right (in this case, as one shell).

Two shells – Two co-planar surfaces colored

Two shells – Two co-planar surfaces textured

One shell – Two non-co-planar surfaces textured

Avoid Floating Shells / Geometry Although floating (unsupported) shells/geometry can be perfectly acceptable for rendering an architecture scene, an animation or a virtual walk-through, it is not favorable for models intended for 3D printing. Identifying floating geometry prior to printing will help ensure that your model prints correctly. Unfortunately, in many cases, identification of floating geometry isn’t often determined until after the model has been printed. As such, diligence on the modeler’s side to locate and correct floating shells, via visual inspection (and even ZPrint’s 2D mode) is very important in the modeling process.

For example, shown above is a nicely rendered model of a spiral staircase. However, its WF (Wide Flange) beams beneath/supporting each of the steps (as seen in the top right image) are floating free from the center pillar. As such, all joining geometry associated with the WF beams (steps, railing posts and railing) are collectively floating free from the pillar and will print separately during the printing process. To correct this, and make certain that the staircase is joined to the pillar when printing, we can either make the diameter of the center pillar slightly larger until the WF beams intersect the pillar, thus joining everything together (as shown in the image to the right), or we can extend/extrude each end of the WF beams so that they intersect the pillar.

All WF beams are floating free from the center pillar

WF beams are now joined to (intersecting) the pillar

Let’s take a quick look at how ZPrint’s 2D mode can help identify floating geometry. A floor (a second shell) was added to our previous one shell brick wall model. Our goal is to have the floor and walls print out as one complete part. Let’s open our model in ZPrint, and then initiate “2D Mode”, as shown below.

Open model in ZPrint Initiate 2D Mode ZPrint’s 2D mode allows us to see a layer-by-layer view of our model as it will print along the Z-axis. The image on the above right is layer 0 of our build. The black square represents the first layer of the floor. Anything black will print, anything white will not print. If we move to layer 76, as represented by the yellow layer line in the bottom left ZPrint window (below left image), we can clearly see that the floor is printing correctly. However, when we move to layer 77, we no longer see the floor. Instead of seeing the “black” representation of the walls, we see nothing but white (below right image). This is a clear indication that our walls are floating above the floor and will not be joined to the floor when printed.

In fact, it isn’t until layer 89 that we finally begin to see the first layer of the wall, as shown below. To correct this floating geometry, we can either return to the original modeling application to make the necessary corrections, or we can use ZEdit Pro.

Smallest Printable Feature (SPF) – Minimum Feature Sizes We are often asked what the smallest printable feature (SPF) is on ZPrinters. Since all AEC models are different in scale, overall design and complexity, it is very difficult to provide an exact minimum printable feature size to support the gamut of various models. Although SPF values will vary by model, material, and printer settings, general SPF values for zp150 (with a default layer thickness of 0.004 inches) are following: Load bearing features (at intended print size): ~0.12 to .20 inches (3 to 5 mm) Non-load bearing features (at intended print size): ~0.06 to 0.12 inches (1.5 to 3 mm) Ornamental/fine detail features (at intended print size): ~0.02 to 0.04 inches (0.5 to 1 mm) Load bearing feature examples: walls, columns, window frames (in some instances), and any features

that overhang without support. Please note that walls and other critical support features may need to be thicker than the above general SPF values, and will vary by model. If the design permits, thicker is often better, making it easier to excavate, gross/fine depowder and infiltrate your 3D printed model. Certain delicate structures may require the use of a “non-contact” fixture to cradle the structure to help minimize warping and breakage during part removal, de-powdering and finishing. With a little experience you will gain a better understanding of what is printable and what will survive the finishing process. If you are unsure of the durability of specific features, it may be helpful to test print these features (or an abstract representation of them) to prove the robustness of certain elements. To help best illustrate SPF, below is an example of an internal/external model of a one story, single family, residential home with a removable roof (to reveal the interior walls and other interior details).

Load bearing features - scaled to print - thick enough to keep structure together ~0.12 to .2 inches (3 to 5 mm)

Fine detail f eatures - scaled to print ~0.02 to 0.04 inches (0.5 to 1 mm)

Non-load bearing f eatures - scaled to print ~0.06 to 0.12 inches (1.5 to 3 mm)

Example: Suppose that we wanted to 3D print a stadium model. Assume the dimensions of the stadium are 600 x 600 x 150 feet. If you were to 3D print this model at the ZPrinter scale of say, 8 x 10 x 8 inches, we get a 900 times reduction in scale! This means that the “Megaton” screen that, in real life, is 40 x 30 feet will be scaled to a half-an-inch in our 3D print. Provided that the screen has sufficient thickness, support, and is a watertight solid, the screen will print correctly as a recognizable feature in the finished print. However, we begin to see problems when we consider features on the scale of, say, a railing somewhere in our stadium; our railing that is originally two inches in diameter is now reduced to 0.002 inches (0.05 mm). Features this small cannot survive the excavation and finishing process and need to be either sufficiently thickened or removed before print. Strength and Support To guarantee a model’s ability to survive the post processing / finishing process (excavation, depowdering and infiltration), artificial supports may be needed. Artificial supports are any structural supports that are not part of the original model. We can divide support geometry into two categories; integrated and removable. Integrated supports are supports that will become part of the model, even after the finishing process. Examples are the thickening of walls, windows, columns or the addition of interior columns or arches. Removable supports (or fixtures) are structures that are built to support a given feature during finishing, and are then disposed of, leaving the final intended model. An example of a model requiring a support could be a long roof overhang covering the entrance of a building. Printing this overhang and the building that it’s attached to, will print fine, but as you excavate your model from the 3D printer, the overhang could be damaged. To avoid this, we can construct a simple support piece (perhaps a basic cube) that supports the overhang long enough for us to infiltrate it, after which, this temporary support can be removed and discarded. Example: A 3D model of a high-rise building is to be modeled and 3D printed (based on drawings of the building’s structural skeleton provided by structural engineers). It is made of glass, steel, aluminum, concrete, etc. Each floor in the 100-story high-rise is, with exception to its outer support skeleton, basically empty space, with very few internal support columns supporting each floor. If you were to 3D print this model at the ZPrinter scale of say, 8 x 10 x 8 inches, the resulting geometry would be very thin, and it would be both a challenge to remove trapped powder from within the closed-off floors and post process the model without damaging the very fine structure. One way to ensure the strength of the high-rise is to simply thicken the shell(s) of the building, and add a few discreet interior support columns (an example of an integrated support structure). Adding drain holes to remove trapped powder from each of the floors would also be required. Other options may include modifying existing geometry, like thickening existing support columns beyond their true scale, or modeling custom tailored supports to meet sufficient strength requirements. It is best to err on the side of extra support and thicker walls to ensure survival during the finishing process. If you are required to construct a cut-away section (a removable section that reveals the interior of the building), then your task as a 3D modeler may be a bit more challenging. A combination of integrated and removable supports may be your best option for complicated, hollow, thin-walled, and/or overhanging projects.

Hollowing Your Model If attention to exterior detail is your only goal for your high-rise 3D building model, another way to guarantee strength and support would be to model your building as a complete solid. However, since a complete solid building model, if printed at a rather large scale, can be both heavy and use more consumables (powder, binder and infiltrant), hollowing/shelling (or performing a Boolean operation) and adding a drain hole, is a great way to save on both weight and material consumption. Hollowing/shelling and adding a drain hole will allow you to remove unused powder from the interior for future use.

A complete solid building model with base Building attached to base

Hollow/shell the building and base

to conserve on materials Completed building model

Managing Shells As previously mentioned, an overall architecture model can often consist of dozens, hundreds, or even thousands of shells. Since each modeler models differently, no two models will contain the same number of shells. Being aware of overall shell count can be very important for larger 3D architecture models. If your model consists of error free, watertight, solid shells and have sufficient thickness to survive the printer excavation and finishing process, your shell count may be of little concern. However, in reality, often times, if not modeled correctly, such shells can contain errors and be problematic, thus requiring attention. Addressing each error shell on a manual repair basis for architecture model files can be a daunting, time consuming task. In most cases it could potentially take less time to remodel the model, than actually repair the many error shells. In addition, a high number of shells create lengthy verification and render times when using repair software such as ZEdit Pro or Magics. As such, knowing how to model correctly for 3D printing purposes will help alleviate many of these errors. When preparing an architecture model for 3D printing, one should ask themselves if all of the modeled shells are necessary for 3D printing purposes. In many cases, many shells can be deemed unnecessary / non essential geometry. Removing Unnecessary / Non Essential Geometry Although your 3D architecture model may contain numerous shells, you should pay particular attention to what your desired goal is for printing the 3D model. For example, if your goal is to create a massing model to display only the exterior shape and design of a building, with no concern for any of the internal floors or interior geometry (internal walls, doors, floors, furniture, light fixtures, bathroom fixtures, etc.), you can deem such internal geometry as unnecessary / non essential geometry, and delete these shells from the targeted model file. This will leave you with significantly fewer shells to contend to, especially if any of these remaining shells need to be repaired and/or thickened. In addition, if your goal is to present a specific portion of an architecture model as a “design concept”, such as an entry foyer of a building (shown below), then you can section your model and print only the section of interest at the maximum scale that your 3D printer allows. Printing at a larger scale will help reduce the number of shells that may need thickening.

Recommended Workflow The ability to create and print 3D models is vastly rewarding. By far, some of the most beautifully printed 3D models are AEC models. The last thing that a CAD designer / 3D modeler wants to do is spend excessive time repairing a model file for 3D printing. After all, there is no need to. Why spend unnecessary time repairing when you can spend that time creating great, beautiful, printable 3D models! The workflow to creating printable 3D models is not a difficult one. It starts with your learning and taking full advantage of the tools offered with your CAD / 3D modeling application. Learn them and know them well. After all, it’s far better to invest time in learning the tools of creativity than it is to learn how to repair complex models. Take full advantage of your software provider’s application engineers, valuable online resources, user groups and online forums for answers to your questions. At 3D Systems, we recommend a simple workflow for producing and printing 3D models on ZPrinters. The learning curve is exponential. Once you learn the basics and apply them, there’s virtually no limit to what you can achieve. If you can dream it, you can print it! To best illustrate this simple workflow, we will use the building model that was shown in the “Hollowing Your Model” section. The simple workflow for a single model is following:

1. Open model in ZPrint – scale and rotate accordingly 2. Review model in ZPrint’s 2D mode to help locate problematic geometry

(such as inverted normals, floating geometry, holes, thin features, etc.) 3. Transfer model to ZEdit Pro for model verification, repair and use of ZEdit Pro tools 4. Save model as ZPR file and transfer model back to ZPrint 5. Save ZPrint build as ZBD file and print your model

ZEdit Pro is a very powerful tool for auto/manual repairing, coloring, adding textures & text annotations, splitting, adding pins & holes, hollowing, adding drain holes, and preparing a model for 3D printing on ZPrinters. It has been optimized to address and identify only those errors that are applicable to ZPrinters. ZEdit Pro is no replacement to working with a native 3D model file in the original CAD / 3D modeling application. In fact, once you learn how to create printable 3D models, you will likely use ZEdit Pro as a companion tool to your original modeling application, instead of as a primary repair tool. Since ZEdit Pro does not offer UV map capabilities, its texture map capabilities are certainly not as robust as 3D packages such as Lightwave, Maya and 3ds Max. Nonetheless, it allows users to add color and textures to supported file formats to produce beautifully colored 3D models. Included with the purchase of a ZPrinter, is one perpetual stand-alone license or one floating network license for ZEdit Pro. Take advantage of this software. It will help make models that were once not printable, printable!

Open 3D model in ZPrint Scale and rotate accordingly

Initiate ZPrint’s 2D Mode

Step through the 2D layers to see if there is any problematic geometry.

At layer 1207 we find that we have an unintended hole.

Transfer model to ZEdit Pro Select Fix Model button

Model is verified and reveals 19 verified shells, 1 shell with errors

There is a gap error in one of the windows

Using auto repair, the gap is filled

Use paint tool to color the window surface to match the other windows

Change to repair color mode to check normals

Repair color mode allows us to check for inverted normals – pink indicates that normals are facing in the correct direction – a light blue color in repair color mode indicates inverted normals. Since our model is now fully repaired, we can use any of the other tools available to us in ZEdit Pro, if desired, before saving as a ZPR file, and transferring the model back to ZPrint.

Our hole is now repaired We can create another copy of the building, if desired, and print our 3D models

As you have just seen, the recommended workflow is very simple and effective. ZEdit Pro can be launched directly within ZPrint, or it can be used as a stand-alone application. As you get more familiar with the process, you may decide to tweak the workflow to best meet your needs. For example, one may decide to periodically export sections of a model during various stages of development to VRML, and follow the workflow above to make certain that there are no errors. One may also decide to try to repair any large errors in the original modeling application and learn by their modeling mistakes to prevent such errors in future models. ZEdit Pro is a perfect companion tool to any 3D modeling program. Repairing your 3D Model The degree of repair that your 3D model may require, and your deadline, will help dictate the repair approach that you decide. If you adhere to the general rules of creating error free, watertight, solid shells, with attention to feature thickness (based on intended print scale), while creating your 3D model, you should have very minor repairs, if any. Repair tools such as ZEdit Pro (offered with a 3DSystems’ ZPrinter) and Materialise’ MagicsRP are great tools to help address such geometry errors. If you have significant shell errors (often the result of a model not prepared using the general rules) and you need to thicken much of your model’s geometry, file repair tools such as ZEdit Pro and MagicsRP can be viable options. However, as previously mentioned, addressing each error shell on a manual repair basis for AEC model files with high shell counts can be a daunting, time consuming task. In most cases it could potentially take less time to remodel the model, than actually repair the many error shells using such repair tools. As such, returning back to the original CAD / 3D modeling application to address geometry errors is often recommended. With a little experience, you will quickly learn how to identify the most common errors, you will remember what types of errors are caused when exporting (converting/translating from one file format to another) from various software packages, and which errors are so severe that they warrant rebuilding rather than repair. More often, you will find that a mixed approach of selective repair and rebuilding is most appropriate. Whether you repair or rebuild, it is best to experiment, backup often, and exercise caution when using automated or “one step” solutions, because it may sometimes create more errors than you fix.

Finally, when using various CAD / 3D modeling applications (particularly parasolid / parametric or NURBS based 3D modelers) gaps can be created in 3D models during conversion (from IGES, for example) to 3D file formats such as STL, VRML & 3DS. Although gap stitching can be performed using many of the original CAD / 3D modeling applications, or with software such as Right Hemisphere’s Deep Exploration CAD file translation and visual communication software, ZEdit Pro’s Gap Stitching Tools can allow you to quickly stitch gaps and join surfaces together, and successfully print your 3D model Files. Alternatives to Repairing your 3D Model Whether it’s a deadline to meet, or lack of resources, there may be times when repairing or rebuilding your model is not an option. In such cases, there are online file preparation services that you can take full advantage of. Two very popular online file preparation services, that can help prepare files for 3D printing, are listed below for your convenience and consideration. The services listed below have been tested and verified by the 3D Systems’ Applications Team. Online File Preparation Services

• CADspan (from LGM Architectural Visualization) offers a software 3D file repair tool, which can take 3D data, and automatically provide a file that is ready for 3D printing, by creating a new mesh that "envelopes" or “shrink wraps” the original data. In addition, CADspan also offers 2D to 3D conversion services.

www.cadspan.com

• iKix provides a full range of services to prepare a variety of drawings and file types for 3D printing. The 3D CAD preparation and file healing team at iKix has years of experience in preparing files for 3D printing and has access to a variety of popular CAD software. iKix also converts any 2D sketch into a printable 3D model. In most cases, iKix can provide a ready-to-print file in one day.

www.ikix.in