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We've seen some pretty impressive bridging with PLA around here (example: http://www.youtube.com/watch?v=hQ1X-N6yio4).
But what about ABS?

Printing the "standard" test cube, I always seem to get some strands that break and "loop".

What's the key to improving ABS bridging performance?
Lower temperatures?
Faster / lower bridging speeds?

Just as a starting point for the discussion, here are my most recent Slic3r settings:

; layer_height = 0.25
; perimeters = 2
; top_solid_layers = 4
; bottom_solid_layers = 4
; fill_density = 0.2
; perimeter_speed = 30
; infill_speed = 40
; travel_speed = 150
; nozzle_diameter = 0.4
; filament_diameter = 1.75
; extrusion_multiplier = 1.02
; perimeters extrusion width = 0.50mm
; infill extrusion width = 0.50mm
; solid infill extrusion width = 0.50mm
; top infill extrusion width = 0.50mm
; first layer extrusion width = 0.50mm

Bridge speed is 30 mm/s
No special bridge acceleration.
Bridge flow rate 1.

*subscribed*

I'm waiting for my squirrel cage fan, have printed the layer fan and had intended on printing a "sacrificial support bridging layer" with the fan and then switching it off for the real stuff.

But if there's a way that doesn't involve hand cutting GCode and having to introduce support structures into the CAD drawings I'm all eyes.

You are on the right track int2str

What I have had the best success with is dropping the bridging extrusion rate down to about .60-.70 and testing from there. I also slow the speeds way down (10-15mm) so it can stretch and cool that first layer. However, Slic3r has a hard time with bridges and I have seen on several parts where it treats the first strands of a bridge like a regular layer and doesn't drop the extrusion rate on that bridge. It slows down, but still extrudes full value and leaves a nice loop for the first 2-3 segments.

Cura is great about it though and I have had great success by using it and it handles the bridges very well. (You have to watch and edit the code though to prevent other issues. More on that in another post on the Rostock max area.)

Here is a video that I saw that changed the way that I set my bridge parameters. After testing with these slow speeds, my issues were gone.
http://www.youtube.com/watch?v=_b6hFFcLh_Q

[img]http://i.imgur.com/ph7ZQZR.png[/img]

I haven't played with the settings from the video yet, but this is what I've been able to come up with on my own. Call this the "before" picture.

In this example, it bridges a single string and then tries to attach the rest of the bridges to that string. Watching it go was impressive, but these aren't the results I'm looking for quite yet.

A layer fan. I spent some time fooling around w/ calibration cubes, and a layer fan and slowing down on bridges makes a huge difference.

I'm using a fan already. I've got 3 40mm fans with JetPad's semi-spherical duct mounted on the effector platform. Layer fans made a huge difference in print quality.

[img]http://i.imgur.com/vNViFax.png[/img]

I have not messed with speeds yet. That's next on my list.

I'd definitely try it slower. Also, you might want to play around w/ temperature, too.

sandy wrote:A layer fan. I spent some time fooling around w/ calibration cubes, and a layer fan and slowing down on bridges makes a huge difference.

Layer fan with ABS?

That's my next move.

I figure the layer fan gives you better bridge strings at the cost of crappy inter-layer adhesion. So switch the layer fan on just for the first layer of a bridge, as a kinda support, and then switch it off for everything built on top.

Jimustanguitar wrote:I'm using a fan already. I've got 3 40mm fans with JetPad's semi-spherical duct mounted on the effector platform. Layer fans made a huge difference in print quality.

[img]http://i.imgur.com/vNViFax.png[/img]

I have not messed with speeds yet. That's next on my list.

That PCB your wires are going to looks really nice. Is he ready to sell them yet or is it work still in progress?