Jul 30, 2018

How To Master 3D Printing Overhangs Exceeding 45°

Your print is not immune to the law of gravity and requires support structures for overhangs beyond 45°. In this article, we tell you how to become a master of such overhangs.

What is an Overhang?

Overhangs are the bane of engineers and designers who work in 3D printing. A 3D printing overhang is any part of a print that extends outward, beyond the previous layer, without any direct support.

To illustrate the concept, let’s look at a real life structure that could be considered to have a mild overhang: The Leaning Tower of Pisa. On the side that’s closer to the ground, we would say it has an overhang of 3.99 degrees. Notice that, when measuring overhang angles, we measure “down” from the vertical axis.

3D Printing Overhangs Beyond 45°

While a concern for Pisa preservationists, most 3D printers wouldn’t have any problems 3D printing overhangs of 3.99 degrees. Usually, overhangs up to 45 degrees can still be printed without loss of quality. That’s because any layer in a 45-degree overhang is 50% supported by the layer beneath. In other words, each new layer has enough support to remain intact and to make printing possible.

However, anything past 45 degrees approaches the horizontal and becomes difficult to print. Such overhangs are prone to curling, sagging, delamination, or collapsing. Exceeding 45 degrees means every new layer has less of the previous layer to bond with. This translates to a poor quality print with droopy filament strands.

This is why many designers try to avoid overhangs beyond 45 degrees. But for those who don’t want to limit their creativity and their designs, the 45-degree rule is not always the best solution.

Many objects need questionable overhangs to function or to maintain their beauty. For that reason, we’ve compiled a number of tips and tricks to help you break free of 45-degree prison.

Fine Tune Your 3D Printer

You can sometimes get away with overhangs greater than 45 degrees when your 3D printer is tuned to perform well and reliably. Replace the build plate, level the bed, clean the nozzle and inspect all the nooks and crannies to ensure your machine is up to speed.

Taking things a step further, you can calibrate your machine and perform all the proper routine maintenance to attain the most accurate build space. You should then go ahead with printing a calibration object. This is the litmus test of your printer’s capabilities and will ascertain if 3D printing overhangs is a possibility.

Tweak Your Slicer Settings

Find the Proper Orientation for Your Model

Orienting your model in different ways changes the angle of overhangs relative to the print bed. In some cases this can significantly reduce the number of overhangs over 45 degrees. It can also have the added benefit of reducing the amount of supports needed.

Reduce Your Printing Speed

A slower printing speed means your material takes more time to bond with the object after leaving the print head. It also ensures that your cooling fan is spending more time channeling air to a given portion of your print. Both effects facilitate fast cooling, which decreases the chances of delamination, sagging, or collapsing.

Reduce Printing Temperature

If possible, print at lower temperatures than usual. Find a spot that is negligibly higher than your filament’s melting point yet hot enough not to cause clogging at the nozzle. Of course, you have to use the filament type that best accomplishes the layer adhesion you want.

While you want your filament to cool fast, you don’t want to compromise on the appearance of your object or its strength. Therefore, go for an excellent printing material that will maintain viscosity and will not cause stringing. 3D printing overhangs will be more troublesome when you are using poor quality filaments.

Reduce Layer Width

When you want to print a problematic overhang, you want as little material as possible to be deposited at any given time, and you can only achieve this by using the lowest layer thickness. A layer with less mass will cool faster, aiding the support of overhangs.

You may also want to configure your shell settings to enable you to print from the inside, out. This technique will provide better support for the upper layers as your print progresses.

Keep the Air Flowing

As mentioned in the previous section, faster cooling filament is less likely to droop. Therefore, you may want to ensure your plastic solidifies as quickly as possible. Make use of the cooling fan or consider installing a radial fan with a blower to displace more air.

Use a Chamfer

A chamfer is a mild slope added to a model to eliminate a severe overhang. Essentially, it ensures that a designer does not violate the 45-degree rule by turning angles that are greater than 45 degrees into 45 degrees or less.

An edge that curves upward, for example, will begin with a very severe overhang angle, which gradually tapers off. Replacing at least a portion of this curve with a single straight edge, a chamfer, at 45 degrees will eliminate the severe overhang.

Naturally, chamfers change the look of a model, which may not align with the integrity of your print. Therefore, a chamfer may not be the best solution to 3D printing overhangs.

Anchor Your Print

You may also want to spend more time designing a model with integrated or hidden supports. The result is an object that has supports, but the design fools the eye into thinking there aren’t any.

Antonio Canova’s “Venus Victrix” is a prime example of how this idea can be executed. The pillow provides support to the right arm while the folds of the toga act as supports for the underside of the left leg.

In this way, Canova simply anchored the parts of his design that would have gone beyond 45 degrees. The artist made his support structures “invisible” and his work looks organic despite having difficult overhangs.

Split Your Model into Multiple Parts

Splitting a complex model into several parts can make printing much easier, especially if the pieces are re-oriented in such a way as to avoid 3D printing overhangs. After printing, simply bond your pieces using an adhesive or a solvent.

Use Supports

If nothing else works, you can always turn to supports. Supports are extra structures printed beneath parts of models that have little to no direct support from the rest of the model. Because they are not part of the actual model, they must be removed once printing is complete.

Often supports are necessary evils that increase material costs, printing time, and post-processing work. On the plus side, they allow for 3D printing overhangs of any angle.

When dual extrusion is an option, one may choose to print supports using a soluble material. HIPS and PVA, for example, are soluble in limonene and water, respectively. Thus, submerging the entire printed object in the appropriate solvent is enough to remove supports. The material simply dissolves over time, leaving your object intact with its difficult overhangs.

In most cases, however, supports are not soluble. Breakaway supports must be snapped off of models, which then often require a bit of post-processing.

License: The text of "How To Master 3D Printing Overhangs Exceeding 45°" by All3DP is licensed under a Creative Commons Attribution 4.0 International License.

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