Bridging in 3D printing: how long can a bridge be

How a bridge is printed

With an ordinary overhang the plastic is laid onto support from below. Under a bridge there is nothing, so the printer stretches the plastic from one edge to the other. The nozzle moves fast, cooling is strong and the plastic sets while still in the air.

The printer starts with straight lines that form the floor of the bridge. Normal printing continues on top. That is why you see thicker strands on the underside and a rougher surface than on a face that sat on the bed.

How long a bridge can be

Short bridges, from a few millimetres up to a few centimetres, come out well, longer ones sag. The limit depends on the material and cooling. PLA handles bridges better than PETG, which is runnier.

There is no exact number, it depends on the model and the settings. If a bridge matters to you, keep it as short as possible. Anything over a few tens of millimetres is better supported, or change the model.

How to design a bridge

• Make the bridge as short as you can.
• For holes with a horizontal axis use a teardrop or diamond shape, so the top is not a bridge.
• Consider turning the bridge into steps with a gradual overhang.
• Do not use the underside of a bridge as a precise surface, the tolerances there will be larger.

Bridges and price

Bridges that cannot hold themselves get supports. We create them automatically and their cost is included in the price per piece. So design important areas so that the bridge does not have to be long.