Bridging Settings

[KeithA]

I was at the Maker Faire yesterday and overheard a discussion about bridging and how it is utilized to print a model that would seem to need supports. Can anyone share there experiences with this and provide the settings that worked the best for them if different from Simplify3D's defaults. I am also unclear under what circumstances this technique would work. They were specifically discussing a heart shaped box created by Emmett and available on Thingiverse. http://www.thingiverse.com/thing:44579 Any info you care to share is appreciated.

Thanks

[jsc]

I just made two models that made significant use of bridging:

• the plaster box mold recently discussed in another thread: http://www.thingiverse.com/thing:335019
• and a multitool belt holster: http://www.thingiverse.com/thing:335122

For the box, the bottom piece of the mold is hollowed out to avoid printing stuff that doesn't need to be there. The bridging distance is 50mm, and since it won't be against the mold the quality isn't important, but it turned out pretty good.

For the multitool holster, bridging is used to avoid support interior to the model, which would be tedious to remove at best. The maximum distance bridging distance is also 50mm, in the belt loop, and about 30mm for the top of the holster body.

Here is a good article about bridging settings; it seems slower is better up to a point. I've found that as well in limited testing.
http://www.3dgeni.us/a-bridge-too-far/

I run bridges at 25% of 80mm/s, but even slower gives better quality. ketil's slic3r profile on github uses, I seem to recall, 10mm/s. That will really slow down your prints, but may be worth trying if the quality is important. I run a bridging extrusion underspeed of 80%, to stretch the filament to avoid sagging. This hasn't been rigorously tested, so you may want to try starting at 90% and working down if you sag too much. There is a bridging torture test by triffid_hunter on thingiverse that people seem to like.

[KeithA]

Thanks for the link. Do you use Simplify3D? I was looking at the settings and there are (3) settings;

Unsupported Area Threshold <Default = 50 sq. mm>

Bridging Extrusion Multiplier <Default = 100%>

Bridging Speed Multiplier <Default = 100%>

I am assuming the last setting is what I need to adjust. I have never adjusted my print speed so it is at the default of 4800mm/minute which is the same as yours. Is the other setting you are referring to the second one from above? I will start with the speed change and try the torture test you suggested.

Thanks

[jsc]

Bridging extrusion multiplier, that slows down the extrusion rate as a percentage of what would be normal for a given speed. You want that to be, maybe, between 80 and 100%, so that the filament is slightly stretched during the bridge. That helps keep tension on it and prevents sagging. If you're feeling vigorous, you should try running some tests with some various values and let us know which one you found to be the best.

Speed multiplier, that slows down bridging speed as a percentage of your normal speed. 25% of 80 mm/s would be 20 mm/s, and that seems okay to me. I haven't run exhaustive tests, I just found some settings that weren't terrible and have stuck with them.

[KeithA]

Thanks for the clarification. I have ran a few test with different speeds but they look very similar. I am not sure if the differences would be so slight or that the setting isnt kicking in like it should. How does the unsupported area threshhold calculate?

Thanks

[jsc]

Try bridging wider and wider gaps until you start seeing some obvious failures, then test at that distance. It should make any performance differences more obvious. If you can't find any, then that's good news and just use the fastest speed you can.

The unsupported area threshold doesn't apply the bridge speed/extrusion settings to bridged areas that are smaller than the setting in sq mm. Short bridges don't need any special consideration. 50 mm^2 is about a 7mm square, but it would be better if they let you specify bridging distance rather than by area; a 26x2mm gap would be bridged at bridging speeds even though it is only bridging 2mm at a time. I don't know why they did it like this.

[KeithA]

I tried the tweaks using the test file from Thingiverse. I made adjustments to be the speed as well extrusion multiplier and was able to only see a very slight difference. Maybe it also has to do with the temp of the extruder figuring that may effect how quickly it cools.