Prusa Slicer - Any Way to Set Maximum Bridging Length?
Howdy,
I just printed an object with some fairly long bridges, and it turned out okay. But with a Prusa, "okay" isn't good enough, so I thought I'd see if I could improve it. Here are some pictures of the object:
The object was printed with the "Maria" letters against the print surface, because there's a stand in the back (which you can't see), that prevents the obvious orientation of printing with the blue part flat on the surface. I had automatic supports on, and they were printed around the perimeter of the rectangle.
As you can see, the bridging did pretty well, with only the two or three longest traces drooping noticeably. The Prusa Slicer software chose the angle at which the long bridges were printed - if it had printed the bridges at the normal 45 degree angle (in either orientation), the longest bridges wouldn't have been so long.
How can I eliminate these long bridges? My first thought would be to have a "maximum bridge length" parameter in the slicer software, so that the software could either adjust the printing angle until all bridges are shorter than the parameter, generate support where the bridges are too long, or warn the user so he could specify some extra support to keep the bridges shorter. (BTW, the longest bridges in this print are about 12 cm.) However, I can't find such a parameter in the current version (2.0.0) of Prusa Slicer.
I do see that there is a "bridging angle" parameter. I didn't consider this parameter, so it was left to zero, which has the software calculate this angle automatically. Now that I know that this parameter exists, I'll definitely consider it when my prints have long bridges. If I had set the bridging angle to 45 degrees, for this print, the maximum length bridges would have been reduced from 12 cm to about 6 cm. In fact, if I had set the bridging angle to 90 degrees, the longest bridges would have been 5 cm, because that's the short side of the blue rectangle (which is 15 cm by 5 cm). I'm not sure how the software works, but it seems like it sets the angle so that bridges are shorter than some particular length but doesn't necessarily try to make them even shorter.
Any comments from you bridging experts would be appreciated.
Thanks,
A.J.
RE: Prusa Slicer - Any Way to Set Maximum Bridging Length?
Turn on support bridging ... modify the support to not be a support, zero interface, but rather pylons that contact the flat surface in defined locations, and reduce the interface distance to maintain part dimensional accuracy. In this example I made supports into four linear pylons that keep bridging well controlled with almost zero droop. So part is still dimensionally accurate even with bridging.
Typical ugly drooping ...
RE: Prusa Slicer - Any Way to Set Maximum Bridging Length?
Tim,
I think you're talking about unchecking the "Don't support bridges" checkbox. Thanks for bringing that to my attention.
My problem with that option is that support material is generated everywhere except where the Maria letters are. I'd like to find a happy balance between some extra support material and some short bridging allowed, in order to keep bridges below some maximum length.
BTW, do you recommend some combination of "Pattern spacing" and "Interface pattern spacing" so that there's enough but not too much support material. I'm just eyeballing it from the pictures you posted, but it looks like you increased the "Pattern spacing" to about 6 mm, while keeping the "Interface pattern spacing" at 0.2 mm.
RE: Prusa Slicer - Any Way to Set Maximum Bridging Length?
That's precisely what I am suggesting. But each model is vastly different and there's no single perfect setting. My example turned out to be 3.9 mm spacing and 0.01 mm Z distance. With the part and the filament my initial trial with 5 mm spacing didn't provide the side to side clearances to fit the gap being supported ... but might have worked had the gap been wider. A full interface layer also would have been a problem because contact would have been too solid and virtually welded with the part.
Here's another view of my initial manual attempt to support the bridge with manually added "fins" ... it worked, but the part thickness couldn't be minimized well enough. So I later switched to auto-supports.
RE: Prusa Slicer - Any Way to Set Maximum Bridging Length?
Tim,
Thanks for that last picture. It gave me a lightbulb moment about what you were talking about in your first post when you mentioned "linear pylons". Maybe that would be a good Prusa Slicer feature request - just generate "fins" for support material, without the crossing layers. Probably would only work for short heights, but for many small holes it would work great.
BTW, in your last post, I think you meant 0.1 mm instead of 0.01 mm. Even with a Prusa, I don't think we're down to hundredths of a mm, yet...
I think another future Prusa Slicer feature would be to somehow inform the user (after slicing) of how long the longest bridges are.
RE: Prusa Slicer - Any Way to Set Maximum Bridging Length?
No - I did mean 0.01 mm ... the idea to allow zero droop. And the fin feature is already there; just turn off the interface layers (0), and ensure the support angle is correct to the part bridging orientation (90 degree deltas work best). Works well for what I was doing.
RE: Prusa Slicer - Any Way to Set Maximum Bridging Length?
Thank you, Tim. I had a similar problem with bridging - turns out that "turn on support bridging" was the solution.
Whoever set an experimental feature as default = on should be shot.