Key Takeaways

  • What are overhangs and bridges? They are parts of a 3D print that extend beyond the layer below, creating an angle with the vertical or horizontal.
  • What is the 45-degree rule? It is a guideline that suggests avoiding angles greater than 45 degrees in 3D printing, as they can cause printing issues.
  • How to print overhangs and bridges? There are several methods, such as using chamfers, support structures, hidden supports, and precise printer settings.
  • How to calibrate the printer settings? It is important to ensure the printer is in good condition, the print bed is leveled, the nozzle is clean, the cooling fan is effective, the print speed is slow, the layer height is low, and the filament quality is high. A calibration object can help test the settings before printing.
Overhangs and bridges

The difference? Bridges on the left, and the right is an increasingly proportionate overhang

An overhang is a part of a 3D print that extends unsupported beyond the layer beneath it, creating a specific angle known as the overhang angle.

The 45-degree rule has long been the standard guideline to ensure stability and successful prints. But in this guide, I’ll share how to go further.

By using methods such as chamfers, hidden support structures, and precise printer settings, one can defy gravity in 3D printing, creating objects that appear to stretch the very limits of what’s possible.

In this guide I’ll share my best 3D printing overhang tips from 5 years of experience, so you can navigate this tricky technique with ease.

Why Would You 3D Print An Overhang?

An overhang in 3D printing is an area of the object that isn’t directly supported by the layer beneath it or the build plate.

Take a moment to visualize the letters Y, H, and T. The Y’s arms form two overhangs at 45° angles, while the T’s crossbar presents two 90° overhangs. The H, however, does not feature overhangs, but rather a bridge anchored by two vertical supports.

In 3D printing, these design elements introduce a particular problem. Our extruded filament is subject to gravity and can’t be printed into thin air. So, how do we deal with this issue?

The solution varies depending on the object’s shape. Let’s delve into the various strategies to address challenges encountered while trying to print overhangs and bridges.

Understanding Overhangs in 3D Printing

Overhangs

Managing overhangs, especially steep overhangs, is a formidable task.

An overhang extends beyond the layer below it, creating an angle with the vertical. This angle, known as the overhang angle, can range from slight to severe.

Imagine your printer placing each layer with a small offset to create an overhang. As the overhang angle gets closer to 90° or horizontal, the offset between each successive layer increases.

Let’s consider a 45° angle, a common scenario in 3D printing. Here, each layer is offset by 50%, meaning half of the new layer aligns with the previous layer. This offset provides significant stability as there’s enough material for the new layer to adhere to.

When dealing with steeper angles, like a 75° overhang, the offset reaches up to 80%. In this case, less than 20% of each new layer stays in contact with the layer underneath.

This reduced contact surface leads to lower stability, increasing the chances of issues like delamination, sagging, or even collapse of the overhang.

So what can we do to minimise there complications when 3D printing overhangs?

Challenging the 45 Degree Rule

45 degree rule in 3D Printing
This is typically the safe bet – but we’re here to talk about ways beyond this.

The 45-degree rule is a common guideline in 3D printing. It suggests designers to avoid incorporating angles greater than 45 degrees in their designs, aiming to eliminate overhangs and simplify the printing process.

While it’s a general rule that may improve overhang stability, adjusting overhang settings according to the 45-degree rule can limit the beauty or functionality of more intricate and ambitious projects.

Let’s explore the top strategies for 3D printing daring overhangs without compromising on print quality.

Use a Chamfer

Chamfer

A chamfer is one of those ‘cheat’ 3D printing techniques – a symmetrical, sloping surface at an edge or corner that is used to avoid violating the 45° rule.

In other words, a chamfer essentially makes an angle that is greater than 45° and turns it into an angle that is 45° or less. Here again, we have a solution that solves the problem of difficult overhangs by delimiting design.

In some cases, the use of a chamfer might work fine. In other cases, a chamfer could destroy the integrity of the object that you were trying to produce. So, a chamfer isn’t so much a solution to printing difficult overhangs as it is a way to avoid them.

How to 3D print a Support Structure for Your Overhang

Support structures in 3D printing are purpose-built materials, designed specifically to uphold the overhangs in your print. Think of it as a scaffold, providing direct support to the yet-to-be formed segments of your model.

First, your printer sets down a layer of support material beneath the intended overhang area. This creates a supporting surface for the overhang. By adjusting the layer width and layer height, you can ensure a more stable structure for complex designs.

Removing Support

Once the support is securely in place, your printer proceeds to print the upper layers of your model. Once your print is complete, the support structure can be safely removed, leaving behind an intact and well-formed overhang.

Most support materials are designed to dissolve for easy removal. For instance, PVA support structures dissolve in water, while HIPS dissolves in Limonene. After printing, the object, along with its tricky overhangs, is placed in a container filled with the appropriate solvent. The support material disappears, revealing a perfectly printed overhang.

However, not all support materials dissolve. Some, known as breakaway support materials, are designed to physically break away from the object after it cools. These support structures can be neatly snapped off from the printed object, maintaining the integrity of the overhang.

Hide Your Support Material

Another solution is to design your object so that difficult overhangs are supported but, because of the design, the eye is fooled into thinking that no support was used.

This is a trick that sculptors have been using for the last two thousand years. For example, take a look at “Venus Victrix” by the Italian sculptor Antonio Canova.

Example of hidden supports

The right arm is an overhang, but the pillows act as a support. Likewise, the left leg is another overhang, but this time the bunched toga underneath does the necessary supporting.

The point is, with careful design, support for overhangs can be incorporated into an object in such a way that it doesn’t look like support. Instead, the object retains an organic look that naturally incorporates what otherwise would be difficult overhangs.

How To Exceed 45° Without the Use of Support Materials

With certain tweaks in your print settings, it is possible to exceed a 45 angle and improve the quality of your overhangs and bridges.

For example, slower print speeds often allow for better layer adhesion, enabling steeper overhang angles.

Likewise, by refining the layer width and height parameters, you can effectively print overhangs at angles beyond 45° without support.

Let’s examine some strategies to print overhangs more efficiently.

Make Sure Your 3D Printer is Prepared

To successfully print steeper overhangs, it’s essential that your 3D printer is in good condition.

Start by ensuring that your print bed is perfectly leveled. If worn out, replace the build surface to provide a smooth and flat base for your prints.

Check that the print nozzle is clean and clear of any debris, and that your nozzle temperature is set appropriately for the filament you plan to use.

Solidify Your Print Material Quickly

cooling is always important
Cooling is always important. Here on the left, cooling has not been sufficient. On the right, you notice the crisp 45-degree overhang, with sufficient cooling.

As we saw above, angles above 45° mean less contact between each successive layer in your overhang. This increasingly minimal contact means that the longer the material takes to cool, the greater the chances are that sagging, delamination or collapse will occur.

Optimizing your print speed and layer cooling mechanisms becomes essential here. Efficient use of your cooling fan is one way to accelerate solidification. Most 3D printers ship with axial cooling fans, but you may also consider a radial fan upgrade with a ducted blower for even faster cooling.

Try adjusting your printing temperature to slightly above the material’s melting point, but still hot enough to prevent the print nozzle from clogging. Run a temperature tower test to pinpoint your optimal nozzle temperature.

Lowering print temperatures, combined with effective fan cooling, make it less likely that you will experience over extrusion or stringing, which can lead to catastrophic outcomes when printing at extreme angles.

The quality of filament also plays a crucial role in successful overhang printing. Better filaments can generally be printed at lower temperatures without compromising on layer adhesion, resulting in create clean, strong bridges with a smooth finish.

Adjust Your Slicer Settings

First, adjust your slicing software to use the lowest layer thickness feasible. This basic setting reduces the amount of material extruded with each pass of your print head.

The logic here is straightforward: less mass allows for a faster cooling time.

Second, change your shell settings/perimeters so that you printing from the inside out instead of the outside in. This will help anchor your topmost layer to the layer underneath as you print.

Print Speed

Rapid cooling is essential for successfully printing angles beyond 45°. One way to accelerate the cooling process is by reducing your print speed.

This causes a slower flow rate, which means it takes longer for your material to be extruded from the print nozzle to the object. This means your layer cooling fan spends more time directing air flow over a particular section of your object.

So, while it might seem counterintuitive, reducing the print speed can actually enhance the overall printing process when it comes to overhangs.

Once you’ve got your printer up to speed and you’ve dialed in your settings, it’s a good idea to print a calibration object. A calibration object will allow you to test your settings before you pull the trigger on printing an object that you’re going to use.

When it comes to overhangs, there are a lot of designs out there, like this one on Thingverse, that will push your printer and your printing skills to the limit.

3D Printing Bridges

bridging prints

Bridges present much of the same printing problems as overhang 3D printing. The difference is that bridges, by definition, are 90° surfaces supported by nothing more than two vertical structures at either end.

Like any bridge, it is the tension on both ends of the string of print material that prevents the middle of the string from collapsing. In some sense, because of the angle involved, you could describe bridging 3D printing as the most difficult overhang of all.

In general, the shorter the length of the bridge, the greater the chance that the bridge will succeed structurally. Conversely, the longer the bridge, the greater the chance that it will succumb to structural stress.

As a result, just as you are generally in safe territory with overhangs containing angles less than 45°, you are also generally ok with bridge lengths of 5mm or less.

However, as was the case with overhangs, in order to create truly beautiful and functional objects, you’ve got to be able to stretch the limits of what you, your printer and the filament you’re using can do.

After all, at least with bridges you don’t need to worry about 3D printing support material removal. Let’s take a look at some of the techniques that will help you bridge the gap in your designs like never before.

Luckily, bridges are just a variant of overhangs. This means that, by and large, the same techniques that help you print angles over 45° will also help you lengthen the distance that you can cross with your bridges.

3D printing bridges poses similar challenges to printing overhangs. Bridges are 90° surfaces anchored by two vertical constructs on each end. It’s the tension at both ends of the print material string that stops it from collapsing midway.

As a rule of thumb, the shorter the bridge, the higher its chances of success, while extended bridges might fall prey to increased structural stress.

Bridges up to 5mm in length are usually safe. However, to craft truly magnificent and functional objects, it’s essential to push the boundaries of what you, your printer, and your filament can do.

Thankfully, bridges are merely a variant of overhangs. This means that, for the most part, strategies used to print overhangs over 45° will also help extend the length of your bridges.

Learn How to Print Overhangs Without Support

Perfecting the technique of 3D printing bridges starts with ensuring your printer operates at its best.

Rapid cooling of your printing material is equally essential. Just like printing overhangs, the longer your material takes to cool, the higher the chance of bridge deformation or failure. So set your layer cooling fans to the maximum!

Tweak your slicer settings to lower your printing temperatures, and decrease your print speed to increase your filaments exposure to cool air.

High-quality, low-temperature grade material will provide better layer adhesion, resulting in a stronger, cleaner bridge.

To navigate challenging bridges, slightly altering the shape can really help. A flat-bottomed bridge demands a tricky 90° angle, but introducing a mild arch can reduce the print angle to a more manageable 70° – making it significantly easier to print.

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