Over-hangs in prints

Question

I would like to ask this in more of a general sense than anything, just for people to make note.

I am printing out things for people and some files have some edges hanging out the side. I always worry, since it is printing in mid air, that it would screw up the print. But I was able to go, maybe 1mm(I am not to good with metric when it comes to guessing). My question is, how far at 90* from a wall can a printer pull off before it is necessary to have support? This would help me when slicing up files.

Answer 1

It is typical for a 3D printer to be able to manage one-half the width of the nozzle for unsupported layer printing. This frequently calculates out to a realistic 45° from the start point.

If you are getting 1 mm extension from a 0.4 mm nozzle you are doing well. It's possible that the layers are not strongly bonded at the point of extension from the vertical wall, but are then strengthened by the layers printed above, if they do not extend excessively.

If your part is designed well, the extension will be distributed gradually over more than one layer, allowing that 1 mm extension over 2.5-3 layers without impacting the appearance of the model in an excessive manner.

The above does not apply to bridges, as it involves a different dynamic for the printer/slicer software.

Answer 2

If I understand correctly, your question is specifically for overhangs at 90° (so an horizontal plane that has no support under it.

The first to notice is that you can only pull this off if the extrusion happens perpendicular to the surface from which the overhang is coming off (the closest to 90° the better) as effectively what is happening is that you are building a cantilever structure as you extrude.

If you think about it in terms of a cantilever structure you will quickly realise that the stiffer the structure, the furthest you can go without it drooping. The main parameters you can tweak to increase the stiffness are:

• Cooling. The cooler the plastic, the stiffer it is, so crank the cooling part fan up to 100%!
• Speed. Plastic need time to cool off, so the slower you print (within reasonable limits), the more time you will allow for plastic to cool under the fan. On my rig I seem to get the best result between 15 and 20mm/s, but your mileage may vary, obviously.
• Layer height. The thicker the layer, the more weight it will bear before drooping, so higher layers work best. A slicer that is very convenient to use for prints that have a couple of overhangs like these is slic3r PE, as you can vary the height of the layers at specific points in the print.
• Material. Some materials are more rigid than others. PLA is probably the one that works best for overhangs. PETG and Nylon are somewhat more problematic, and flexible filaments are the ones being more difficult to use.

For bridges (unsupported filament extruded between two supported structures) the considerations are identical but for speed: in my experience having the speed not too low helps the nozzle keep tension in the extruded filament by "pulling" it and keeping it horizontal. But again: each printer, firmware and slicer is different, and you should experiment yourself to see what works for you.

To sum this up: "how far you can go before needing support" is a question that cannot be answered with a fixed number as the answer depends from a lot of factors that vary from printer to printer and material to material. Without mentioning: how many defects you are happy to tolerate before calling the print a failure.

Answer 3

To add to what mac described, there are small detail effects which sometimes change the behaviour of an overhang (and not necessarily in a predictable manner).

Concave overhangs might sag (rather than turn out like a bridge). Convex overhangs might pull tight. Cooling plastic tends to shrink,so might sag less.

I'm often surprised how well overhangs turn out, but equally often see failures which I don't anticipate.