The definitive guide to design for 3D printing in 2020

This guide is for product innovators, industrial designers, and budding 3D printing enthusiasts ready to take design workflows up a notch. Master how to prepare and polish a 3D printed prototype quickly, and use these adjustment techniques in a direct modeling environment to push concepts out in record time. All the models in the post were printed on an FDM (fused deposition modeling) printer, ideal for low cost models and rapid prototyping. 

In it we'll cover:

• Nozzle size and material: your choice of printing equipment is directly linked to how fast your product prints and the level of detail that you can achieve
• Design parameters: in order to be printable, your geometry needs to have volume and manifold geometries
• Overhangs and support: beyond a certain point your printed material won't be able to print onto thin air (surprise!) and requires designed 3D printed supports, which will affect the look of your final object
• Adhesion: the heat of the material and printer nozzle may distort the cooling material, unless you print out a support structure to keep it firmly adhered to the printer bed
• Orientation: the direction that the material is layered to create your object and how it will impact the final look and feel of your object

Though it may seem daunting at first, 3D printing your own designs is by far the most efficient way to test and iterate product concepts - making the learning curve well worth the time investment, even in the short run.

If you're keen on leveling up your design workflow, rapidly developing new ideas, and even trying your hand at launching a successful business with a product concept, go through this A-Z checklist of design principles for 3D printing to cover your bases before pressing print. 

 

Watch these principles get put into action

 

Wayne State University industrial design professor Claas Kuhnen, walks through the design process and answers some questions on design issues that might be shaking up your print process. Watch the webinar recording here.

 

The right modeling mindset

 

The most important concept to keep in mind when you’re 3D printing your model is that what you’re seeing on the screen digitally will have to deal with the laws of physics when it comes out of your 3D printer’s nozzle. 

Overhangs that stretch effortlessly out into the ether on your iPad screen will likely come crashing down into a melted plastic mess from your printer. Perfectly concentric holes in your model may better resemble a deflated basketball in the real world. You may find that the thread you’re trying to fit that screw into has nothing to do with the size of the thread on the screw anymore.

To anticipate these challenges, you'll need to pay attention to the following things before pressing print.

 

Choosing the right printing nozzle and material

 

The nozzle size and material will influence the strength, print time, and quality of your final product.

Nozzle diameters generally range between 0.1 - 1.0 mm. When you’re selecting a 3D printing nozzle, you’re deciding how much filament is extruded and how fast, which will naturally produce different results. While a smaller printing nozzle (<0.4mm) predictably extrudes less material than a larger printing nozzle (>0.4mm), the impact this will have on your print is more complex.

The standard nozzle size that most 3D printers come with is 0.4mm. This size lets you print layer heights between 0.1 - 0.3mm, so you can manufacture detailed objects in a reasonable amount of time.

Tip: When you’re choosing a printer head, determine the final use case. If your model is a practical object that needs to be strong and printed quickly, use a larger nozzle. More detailed prints get a smaller nozzle. Here are some general tips to guide you.

 

Use larger nozzles (>0.4 mm) for:

 

• Printing things fast. Larger nozzles equal larger flow rates and more material deposited.
• Increased toughness. Objects printed with 0.6mm nozzles absorb up to 25% more energy than those printed with a 0.4mm nozzle.
• Printing with abrasive filaments. Smaller nozzles easily clog, making them a difficult tool for printing coarser filaments -- opt for a larger nozzle in this case.
• Models with low print resolution. Because they print thicker layers, larger nozzles are best for prints without thin or fine details.

 

 

Use smaller nozzles (<0.4 mm) for:

 

• Small details. Highly detailed models are better served printed with small nozzles that extrude material more finely.

• Many features. Printing with a smaller nozzle inherently takes more time, so it’s only worth your while if you are manufacturing a more decorative piece and have a lot of time. Plain objects make more sense to be printed with a larger nozzle. Example applications for small nozzles include jewelry, text printing, or miniatures.

• Low layer height. Generally speaking, layer height should be 80% or less of the nozzle diameter, so a smaller nozzle will require lower layer height.

• Easily removable supports. Using smaller nozzles will result in a thinner support structure that can be more easily detached from your object after the print.

 

 

The advantage of dual extrusion printers

 

Dual extrusion printers have a second nozzle and extruder, so you can print parts using two different materials, switching between filaments as needed.

With a dual extrusion printer, you can combine a standard material with support materials. By printing supports with a different material, you can easily remove or dissolve them from the final print without leaving any marks. Dual extrusion printers also let you print using two different colors, or reinforce one printing material with a stronger one.

 

Nozzle Material

 

• Brass nozzles

These are the de facto standard for most FDM 3D printers. This nozzle material provides good thermal conductivity and stability. But while it’s the most common, it can’t handle all types of filaments. Brass nozzles are best for non-abrasive filaments including PLA, ABS, Nylon, PETG, TPU, and others.

• Hardened steel nozzles

Unliked brass nozzles, hardened steel wear less when you’re printing abrasive materials like carbon fiber, glass fiber, metal-filled filaments like steel-filled, iron-filled, brass-filled, and other exotic filaments. 

Steel nozzles are 10 times more wear-resistant than brass nozzles, but the possible presence of lead in the nozzle makes them unfit for printing anything that will come in contact with food or skin. A strong lead-free alternative for FDA approved products are stainless steel nozzles, which can be used with light abrasive materials.

• Ruby tip nozzles

Ruby tips are actually made up of a brass body with a ruby tip. The ruby tip increases the nozzle’s durability, and the body maintains good thermal conductivity, making this nozzle type the most precise, albeit expensive for regular use.

 

Solid modeling and manifold geometry

 

Before you print, you need to make sure that your design is absolutely watertight. That means there should no holes on the surface of your 3D model.

If you’re 3D printing a model that you exported from Shapr3D, you can check this bad boy right off your list! All models created on the app are inherently solid models, meaning there are no non-manifold intersecting surfaces.

If you're modeling using surface modeling software, you'll want to post-process your work, clean up any holes and check for any of the kinds of intersecting surfaces or shared edges (collectively called non-manifold geometries) listed below.

Manifold geometries

 

A successful print has to have a manifold geometry. An easy way to understand manifold geometry is by learning what a non-manifold geometry is.

In a non-manifold geometry, when the 3D shape is unfolded, the normals of the 2D shape don’t all point in the same direction due to a shared edge or two faces connected at a single point.

 

Non-manifold geometry can also be a geometry that includes an intersecting edge without volume. Though intersecting edges can't often be seen from the outside of the model, they render the design impossible to print.

Tip: To make sure that your model is printable, see if you have any of the following errors and adjust them to create a manifold shape: 

 

• T-type non-manifold geometry

If you have three faces sharing a single edge, make it printable by adding volume to the third face or deleting it completely.

• Bow-type non-manifold geometry

In this instance, multiple surfaces are connected at one point and don’t share an edge. Either disconnect the two geometries or delete one of them.

Non-manifold geometry also occurs when there's a shape without volume.

• Open geometry

In order to print a geometry, it needs to have a volume, so a shape with “missing” surfaces or no volume isn’t viable. If you think about it, it would be the equivalent of asking your 3D printer to print one straight line and expecting it to come out in 3D.

You can create volume in your model by adjusting the wall thickness or adding additional surfaces to your geometry.

 

 

Wall thickness

 

Wall thickness goes hand-in-hand with non-manifold geometries, as we saw above that geometries without volume can't be manufactured. Walls that are too thin make small parts on the model unable to be printed or very fragile, with a high chance of breaking.

Assess your printing material and the height of your wall to determine whether it needs additional support. A wall that's already bolstered by ribs or webs (we'll get to those soon) can be thinner than a freestanding wall.

Tip: Wall thickness should typically be two or three times the nozzle’s width. Walls with thicknesses greater than 0.8 mm can be printed successfully with all processes.

 

 

Start with a strong base

 

Adhesion is a huge difficulty with 3D printing. If your model, or even a part of it, doesn’t stick directly to the 3D printing plate when the first layer is printed, it could detach and warp your print resulting in mucho plastic, time, and dreams down the drain.

Tip: avoid large flat surfaces and round the corners of your 3D models to enhance the success of a clean print

Printing with too high heat and not allowing the first layer to cool properly will increase the risk of a bulge, and make it hard to fit pieces together. Affectionately named ‘elephant’s foot,’ this mostly appears with larger parts where the weight of the object pushes down on the first layer. 

 

 

 

• Add a ‘raft’

Sidestep this issue by adding a raft for your "foot" to land smoothly on. A raft in 3D printing is simply a flat surface area made up of horizontal latticework, added beneath your part. It helps eliminate elephant's foot and improves adhesion to the printer bed.

 

• Work with a ‘brim’

You can also avoid your model tipping over in a bizarre reenactment of technical harakiri by creating a brim underneath it. A brim is a skirt attached to the edges of the model printed with an increasing number of outlines to create a large ring. Brims create suction and hold down the edges of your part by helping it stick to the bed. They’re much faster to print than rafts.

 

 

• Warm up your nozzle with a ‘skirt’

Finally, you have skirts. Sometimes, elephant’s foot is the result of an unleveled build plate or incorrect nozzle height. 

Skirts surround the part but don’t actually touch it, and help warm up the extruder by establishing a smooth filament flow. By observing the skirt quality, you can adjust any leveling issues before printing your model.

 

Tip: Besides printing with a raft, skirt, or brim, you can also lower the bed temperature by 5° C increments or as a last resort, alter your model by adding a 5° chamfer on the bottom edge of the print to mitigate the bulge.

 

Overhangs

 

Overhangs are fun to design and hard to print -- here’s where gravity really puts up a fight.

An overhang that stretches out beyond 45 degrees will require you to include supports so that your build doesn’t tip or start getting messy. There's nothing wrong with supports, but unless you print with a soluble material using a dual extrusion printer head, they'll probably leave a mark when you take them off.

Tip: As a good rule of thumb, you can get away with about 1-2 widths of a print path without supports. Everything else will require printed support.

While supports are doable, they’re not always easy to remove and will likely leave a rough spot or mark on your print.

The image below shows a 'Y' model with arms that begin with an overhang less than 45 degrees. Notice that further up the arms the print begins to get wonky, where the overhang reaches beyond 45 degrees and would require supports.

 

Follow the 'YOTH' rule

 

• A Y-shaped overhang less than 45 degrees can print easily without any need for support. If it's over 45 degrees, count on adding supports

• “O” shaped overhangs, or holes in most cases, create more concentric circles with supports included

• "T" shaped overhangs beyond a 1-2 vertical layers require supports

• “H” shaped overhangs depend on the size of the bridge between the two vertical geometries. Check your printer and print material to see how long of a bridge you can print without supports.

 

Designing supports in your slicer software

 

If you do need supports, create them in your slicer software. Here's what that looks like on Lulzbot's free CURA slicer interface.

You can also design custom supports in your modeling software that are easier to snap off and take up less surface area. Conical supports taper at the top to support your print while printing faster and using less material.

 

Regardless of size, removing supports and polishing your prototype will take some work after your print.

 

Printing holes

 

Holes are a special kind of 'overhang,' that are especially tricky for 3D printers to print. These shapes require the machine to create a round shape by layering materials on top of each other. Because the final layer at the top of your circle will be straight, the end result is a hole that's not quite round and doesn’t quite match the diameter of the hole in your model.

 

You can print out the hole with the slightly flatter top, and use a screwdriver or similar tool to round it out after it's finished. 

 

Bonus tip: Teardrop and slot designs for holes

 

To deal with the pesky issue of holes, you can also try designing a few additional tweaks in your model. One alternative is to model a teardrop-shaped hole in your geometry. This way you can use the hole for its intended purpose without having to drill out the additional layer at the top of the hole. 

This technique means you can avoid having to use supports, but it only works if you orient your part facing upwards, which limits object rotation.

In the same vein, you can add a slot underneath a hole that you need to insert a rod into, which allows the hole to expand. Then use two clamps to secure the hole together. 

 

Ribs

 

If you're printing a piece that has a protruding feature jutting out from the base, you'll run the risk of that piece breaking, even during the printing process. 

To avoid broken 'arms and legs,' add triangle supports or 'ribs' around protruding pieces to support the base. Ribs strengthen fragile protruding features by supporting perpendicular angles. Without additional support around their bases, these structures are more likely to snap off.

 

Webs

 

'Webs' are another form of built-in support used to maintain the integrity of shells. They consist of a network of supportive structures and protruding pieces that help a body keep its shape without having to print a solid structure (saving hours, or even days). If you're testing different shapes and ergonomic structures, design webs or infills into your object to speed the process along.

 

Threads

 

Threads are hard to print because the heat can contract the details and make it unusable for your original purpose. This is increasingly true, the smaller and more detailed that the threads get.

Before printing, add an additional tolerance between .5-1mm to your model to make up for any heat shrink or imperfections. Small blobs on a tight-fitting thread will act like sand in a gearbox, making it impossible to screw the part on.

To create a better thread, round the crest and roots in the design process - sharp edges tend to concentrate stress.

Alternatively, you can design additional ‘dog point’ heads onto your screw. This flat, unthreaded tip helps a successful print and is helpful for locating a groove on a shaft. A dog point head should be at least 0.8 mm in length.

 

Infill

 

If you’re designing a large part, you can save both time and material by considering different infill patterns that use less material. You can manipulate these in your 3D printing slicer. Infill patterns are made up of hollow, geometric shapes -- the density and shape of the infill will affect the strength of the final printed material.

Hexagon or honeycomb infill is the strongest, most efficient infill and also the fastest to print. Honeycomb infills mimic naturally occurring hexagon patterns used throughout nature.

You can also explore printing a ‘wiggle’ infill if you want your piece to have more of a twist. Triangular infills have a high lateral load-bearing capability, making it a good choice for bridges.

 

Orientation

 

Orienting your parts mindfully can significantly improve the strength, appearance, and print time of your piece. Objects that are manufactured in additive layers are strong in the direction parallel to the layers.

When you’re designing your piece, think about whether any of the parts will be load-bearing and in what direction. Then orient the part accordingly.

As a rule, orient cylindrical features like columns vertically for a smoother surface finish. Orient holes with faces parallel to the XY plane for a better resolution as well.

 

Exporting your STL file

 

When you’re exporting a file for 3D printing, always use the highest setting STL file. STL files are a list of triangles, and cannot store separate bodies. As such, an STL export of touching bodies may actually merge -- make sure to separate each body where possible.

For graphics, export in medium or experiment with a low setting. You may need to remesh or generate a quad mesh if the mesh isn’t uniform. If post-processing is required, export using the highest setting.

 

It's time to get your hands dirty

 

There you have it, the top design considerations to cover before 3D printing your prototype.

If you're ready to manufacture your model, save yourself from shaking your fist at gravity, go through and assess these factors one last time:

• What printing nozzle and material you're using for your use case
• Wall thickness and overhang angles and lengths in your 3D model (and how they'll hold up in your 3D object)
• Model orientation
• Build plate adhesion
• Infill patterns

Of course we'd love to know -- have you tried any of these techniques before? If you've got questions about the execution - watch the complementary webinar recording on 3D printing techniques, or ask us in the comments and we'll get back to you. Tag #shapr3D or @shapr3dapp on Instagram to show off what you've printed with the app!