Check out this bridge distance!
Just over 2" of span with hardly any sag. Using this high efficiency part cooling fan:
Rigidbot single head cooling fan mount Rev-2 by JP1 - Thingiverse
This setup is testing a new PLA filament from Vortex 3Dp (retraction settings still need to be adjusted) on a modified RB3 from ReliaBuild 3D with a side mounted extruder cooling fan that can be found here:
The part cooling fan helps keep the ooze to a minimum but also cools the little branches that did appear to the point that they don’t stick hard and just brush off the finished print.
Not a bad print for testing out a prototype case for a new Wifi/touch screen interface. Very pleased with the performance of this machine.
Just when you think it won’t go any further, something happens. I designed a cassette rack and to save plastic put slots in the base thinking that bridging would occur across them. Nope! It bridged lengthways over 120mm! The part failed not because of bridging but for a tangled roll.
As the filament cools it shrinks a little and stiffens up helping bridging. I’m using a nothing special cobbled together i2 clone with an E3D-V6 hotend that at the time had a 0.4mm nozzle in it.
Looks interesting; What’s your slicer setup?
I keep being amazed at how long a span these things can make, given good cooling. I’ve done 50mm overhangs with the e3dv6 and nophead’s fan duct, with so little sag i didn’t notice until I looked more carefully at it just now. I’ll have to try for even more.
Wouldn’t it be possible to do this from software and print in a bowed fashion so that when sagging, until hardened, the line would end up straight?
@Florian_Ford bridging is easier when you can anchor it on two sides. If it is bowed up, the bottom slices would only be anchored on one side and would sag in their own weight.
@Duncan_Gunn The slicer I use most is Cura V15.04.6. It actually has little to do with the bridging ability of the printer.
Second half…
The part cooling setup is 99% of the key here. I love what this part cooling fan allows me to do with my prints.
The part cooling fan has a high static pressure and no turns or obstructions in the duct so the full pressure drop takes place at the exit in a very focused path crossing right at the tip of the nozzle. No temp fluctuations of the hot end.
I bridge at full print speed and layers of 0.1mm (thin layers have less mass to cool and less weight to cause sag) with the fan cooling at 100%. It cools very quickly.
I can also print slanted overhangs 30 degrees off horizontal (0.4mm nozzle) with no support material. With 0.05mm layer height this drops to 20 degrees. No curling.
The longest I have bridged is 96mm with less than 0.3mm of sag in the middle. I could likely do longer I just have not tried it. I can also do 5mm horizontal cantilevers 3mm wide straight out and they are flat by layer 4 (0.1mm layer). Here is a torture print to try out if you would like: Bridge and Overhang test by JP1 - Thingiverse
You can check out these other posts that show what kind of geometry I can do with no supports. 
1:10 scale T-Rex
https://plus.google.com/u/0/113930448883604105560/posts/izXxWxH3oxr
14" tall single print Eiffel tower
https://plus.google.com/u/0/113930448883604105560/posts/4HhzQbi9MGJ
