Plastic gets extruded over a gap from one point to another. When bridges are messy, the plastic strings sag. The plastic should be cooled very quick over a gap for a solid connection in-between. For an optimal performance, good calibration in bridging settings and cooling is needed. If the way is too far for bridges, use supports.
Adjust bridge setting
Bridges are difficult to make for the 3D printer. In most slicing programs there are settings for bridging. Plastic shrinks when it cools down. This is an advantage at the bridging, because the strings go up and make flat surface. Try a lower extrusion multiplier and a lower speed multiplier for better bridging behaviour. More plastic would induce a drooped string. The next layer would hang down to a bad bridging.
Add support structure
An easy way to get better results are support structures. We can´t recommend which settings are the best, because they change when you change layer height or material. We recommend starting with the standard settings in your slicer program, if you must change them, try the try and error method 😉 Keep in mind, that support material takes additional printing time and sometimes optimization of your models’ placement is another solution.
Part Cooling fan
For a fast cooling set the fan to a high percentage, that the plastic becomes hardened before getting sagged. There are special overdrive settings for bridging, where the fan can be risen.