Bridging –connecting two raised components of a 3D printed part with unsupported layers of filament– is a finicky process that takes a bit of practice and adjustment to master. However, you can achieve unbelievably long 3D printed bridges if you find the correct settings for your filament, printer, and design.
A 3D printer can bridge from one edge of the print bed to another. With the proper settings and a large enough printer, you can create bridges without additional support structures that span 500 mm (20 in) or longer. However, bridges of this length are usually fragile.
If you’re curious about how to create longer 3D printed bridges, this article is for you. I’ll tell you how 3D printed bridges stay intact and offer you some tips and tricks for creating longer, more stable bridges in your 3D printing projects.
Does Bridge Length Affect the Durability of Your 3D Print?
Bridge length affects the durability of your 3D print since the longer the structure is, the more warped and bent the middle will become. Due to this, longer bridges are generally much weaker than short bridges.
Bridging in 3D printing follows the same rules of physics as real bridge engineering – you’re just working with plastics on a much smaller scale.
Bridges stay up because they’re designed to feature one post or other strong structure at each end of a straight or convex plane. These supports provide the necessary compression and tension that allows a bridge to hold its weight without collapsing.
However, the farther apart you move these supports, then the less tension and compression the bridge will have. At a certain point, the bridge’s resistance will become so low that its weight overpowers the material’s tensile strength, creating a collapse in the middle of the plane.
Following this reasoning, the longer your 3D printed bridges are, the weaker they’ll become. However, the point at which a 3D printed bridge collapses will depend on other factors, such as your print settings, the height of your support structures, and your filament’s flexibility and durability.
How Long Can a 3D Printed Bridge Be Before It Starts To Fall Apart?
A 3D printed bridge can be around 250 mm (10 in) before it starts to fall apart, provided you printed it on a personal 3D printer with a thermoplastic filament. However, with careful adjustment of settings and design, a bridge can reach around 450 mm (18 in) before it begins collapsing.
You can print bridges of any length as long as they fit on your build plate. However, your success and the bridge’s strength will depend on the filament and how carefully you adjusted your temperature and extrusion settings before starting the print job.
For most people printing at home with a PLA filament on a budget printer like a Prusa Mini+ or Ender 3, you’ll notice layer separation and sagging on bridges of around 250 mm (10 in), even if your settings are ideal.
Although, when working with a larger printer, you may be able to print longer bridges without experiencing any significant sagging until you reach the 400 mm (16 in) mark.
If you want to see an example of how long your bridges can get before they start to degrade in quality, check out this YouTube video from The Epiphany Channel:
What’s the Best Filament Type for 3D Printing Bridging?
Believe it or not, your filament type will make a massive difference in how easy it’ll be to print a bridge.
The best filament type of 3D printing bridging is PLA. Compared to most filaments, PLA has a relatively low print temperature and quicker cooling rate, which helps the bridge stay intact. PLA is also easy to use and won’t warp very often, typically creating straight and stable bridging effortlessly.
Although PLA is one of the best choices for creating 3D printed bridges, you can use any filament.
Still, suppose you want to use a tougher filament, such as PETG or nylon. In that case, you’ll have to take more time to fine-tune your settings and run tests to reduce warping, improper layer adhesion, inconsistent extrusion, and uneven extrusion cooling.
Tips for 3D Printing Longer Bridges
Since your 3D printed bridges depend so heavily on the proper printer settings, here’s a list of some things you may need to adjust:
- Turn up your fans for faster cooling. The cooling rate of your filament will play a massive role in how durable and straight your bridges will be. Gravity will pull it down if your filament stays warm and soft for too long, creating a saggy bridge with layers of loose filament sagging near the middle. Try turning your fans up to 80 to 100% when you print a bridge and fiddle with the fan speed until your layers stay rigid and straight.
- Slow down your print speed. If you print your bridges too quickly, the filament may have some issues adhering to previous layers, and the weight of a new layer might introduce more sagging in your bridge. Reduce your speed by around 10mm/s (0.39 in/s) and keep going down until you see the results you want.
- Lower your temperature. If your filament is too hot, your bridge won’t stay upright, creating a hot lumpy mess on your print bed. You should generally lower your average printing temperature by about 18° F (10° C) for the best results. The filament will cool faster with the lower temperature, giving you a more solid, less sagging print.
- Add supports whenever you can. Just because your printer can print impressively long bridges doesn’t mean you should throw out the idea of using supports. No matter what you’re printing, using supports in your design can dramatically increase your chances of success. It’s an excellent idea, especially when you’re working with something as demanding as bridging.
- Lower your extrusion rate. If your printer extrudes too much filament in each bridge layer, it’ll have difficulty cooling fast enough to stay intact and fight gravity. Thick layers will also be heavier, increasing the chances that your bridge will collapse before you can even take it off the print bed. Try to lower your extrusion rate (or extrusion multiplier) in small increments if you notice your bridge caving in before it’s finished printing.
- Practice. Unfortunately, no one print setting will work perfectly for all printers and filaments. To create sturdy, long bridges, you’ll have to find the best temperatures, cooling rates, extrusion settings, and designs for each filament you use every time. Finding these ideal settings and conditions will take lots of time and practice, so be patient and keep testing to find out what’ll work for you.
While working through these tips, you may want to run a bridge test on your 3D printer. These basic 3D prints are just for testing your printer settings and filaments on bridges of various complexities and lengths, so making them is an excellent way to see what your 3D printer can do.
I recommend starting with something like the Customizable Bridging Test by Walter on Thingiverse, which has an attractive helix shape and customizable bridge lengths.
3D printers can bridge as much space as you have on your print bed, yet if you don’t carefully adjust your print settings, even your shortest bridge may collapse. However, with the proper care, you can make bridges longer than 400 mm (16 in) without sacrificing durability.