Overhangs, bridges and supports

The 45 degree rule

Every layer rests on the layer below it. A wall that leans outward still works as long as each layer has enough under it. Up to about 45 degrees from vertical, nearly every printer manages without supports. Many printers with good cooling go to 60 degrees.

Past that, the edge of each layer hangs in the air, sags and leaves a rough underside.

Bridges

A bridge is a flat span between two points, such as the top of a window or a slot. The printer stretches the plastic across the gap. Short bridges of 20 to 30 mm usually come out fine. Longer ones sag in the middle.

Bridges print better with the fan at full speed and a slower bridge speed in the slicer.

How the models here deal with it

The generators on this site are designed to print without supports wherever that is possible: overhangs are cut at 45 degrees, holes on a side wall get a pointed or flat top, and parts are laid on their widest face.

If a tool does need supports for some settings, its page says so in the print tips.

When you do need supports

• Use tree (organic) supports for round or irregular shapes. They touch the model in fewer places and break off more easily.
• Use normal (grid) supports under large flat areas, where tree supports leave a bumpy surface.
• Set supports to "build plate only" when you can. Supports that start on the model leave marks on it.
• A top gap of one layer height (for example 0.2 mm) is a good start. A smaller gap gives a smoother underside but is harder to remove.

Often you can turn the part instead

Before adding supports, try another side down in the slicer. A hook printed lying on its side needs no supports and is stronger too. See the guide on print orientation.