Today's video is a bit of a stretch.
So, bridging. Specifically bridging in cura.
It's still an experimental mode as it has been since it was introduced some time in
2018 which means it's been experimental as long as many of us have been printing.
2018 seems so long ago, apparently it was the date the ender 3 was released too.
Anyway bridging is off by default but what is it and what does it do? And should you
turn it on? And just exactly how far is a bridge too far? And why
am I asking questions to nobody when I obviously already know the answers?
Also who's the sponsor of this video? PCBWay is of course. Did I bridge that one
well? Yes of course I did. Do you need PCBs made because making them yourself is a horrible process
involving all sorts of nasty chemicals? Yes you do. Do you want multi layer PCBs? Yes you do.
What about purple ones? Obviously. I have a project coming up which needs
PCBs and I guess I need to choose a colour so let me know in the comments which colour
you would like me to use out of these colours here, I'm kind of thinking blue.
Anyway - PCBWay is easy to use for ordering PCBs, you just upload the files that your design program
spits out like I've been testing fusion 360s PCB creation ability and it's actually pretty
easy to just export that and load it into PCBway's quick order page, and away you go,
PCBs! Thank you to PCBWay for sponsoring this video and now back to bridging!
So Cura is already quite capable of bridging gaps which is why I guess many people don't
realise that there's a separate bridging mode in the experimental section or they just
forget to use it or maybe choose not to because hey we havent got to the comparison
bit yet so is it even better? Bridging just means printing on air between two points,
I mean the name is kind of self explanatory, making a bridge, right?
This is cura bridging gaps in its normal mode, it does the perimeters and then it just kind
of infills it with your chosen infill, thats top/bottom infill, not the other kind of infill,
we have a naming problem here, I know. This works fine. Until it doesn't.
The thing is there are several things that could potentially improve bridging
performance and the first is to bridge at a different speed to the rest of your print,
namely slower, and using cura's bridging settings allows this.
You can also improve bridging by printing at a lower temperature because many filaments perform
better at bridging because they are more viscous, but cura doesn't currently support that idea,
hey that would be cool wouldn't it? You can also vary the fan speed, I guess I'll explain that. If
we check ultimaker's own documentation we can see the fans should be at full speed while bridging,
so why would you want the fans any lower? I think that's an open question, but the settings guide
gives this explanation which I'll let you read yourself, the TLDR is that the default value
is wrong and I've been bridging wrong in some of my tests but OH WELL. I guess I'll
try side by side and we'll hopefully see on screen now if I get chance during editing.
As to why you can enable multiple layers in bridging, well this is all about
weight. I'll show you. When you bridge the first layer, everything looks fine.
But as you add more layers, the first layer then starts to sag because it's
holding weight. If you look at a finished part you would never assume that the bridging was
perfect until it wasn't. So to get less sagging the idea at least is to put more
lighter layers until you have enough structural integrity to be able to print normally.
There's a whole treasure chest of information about this in the settings guide for further
reading, and I recommend reading it, if I covered all of it this video would be an hour long. I
have previously made a video about the settings guide so go watch it if you dont know about it.
So. How good IS bridging, and how far can we bridge?
Here's some samples of bridging on vs off. What do you think?
Interestingly at least on my config other slicers like prusaslicer
use this kind of bridging by default so they must be confident it works better.
How far can we bridge? Actually pretty far. Over distances up to 100mm, that's 10cm,
the results are very acceptable in my tests. Over that it still works but you start to get some
collateral that you need to clean up afterwards. I even printed across the
whole bed on the sovol sv01 pro which is a 280mm bed, and posted it on twitter..
...and then was compelled to try diagonally too. I think we were
hitting the limit at this point though, it didn't fail, but I don't know if it would be useful,
actually honestly I think in terms of usefulness we should probably stick to 10cm or below
BUT that is way higher than most people expect to be able to bridge without support,
and that is what bridging offers, it offers avoidance of support material,
and actually in some cases could end up neater than if you used support material. So I suppose
we have to consider when bridging is better than "traditional support" and what are the limits?
Let's look at this model. Bridging won't work, because as you can see by this failure here,
you can't print curves over fresh air. Or can you? You see it occured to me that bridging is just
about laying down a scaffold to print over, and there's no reason you can't design
that in. I can design a layer under my part in CAD to give cura some guidance for how to bridge.
I found it somewhat hilarious that when I tried this though, cura doesnt seem
to quite understand what I'm trying to do - and prints the lines in an order that...won't work.
But you can again help cura to understand by separating your bridging line order into layers,
so what I have done is put first a simple bridge on one layer in CAD,
then added the triangle supports in the next layer,
and then the full pattern. And cura has to slice those lines in order now.
And it came out pretty well considering. So, the take home there I guess is that sometimes if you
know your part is destined for FDM printing, you can include some "guided bridging" I'm
just making names up now, into the design. I think that's pretty cool.
Finally another trick that's not a trick but I'm calling it a trick. Let me show you this part.
If I printed this, it would fail, because there's nothing to support this central region.
This one even more so. There is a setting with the catchy name
Bridge Sparse Infill Max Density which is supposed to be to stop pillowing which is
what you get when the top layer just looks like a rag draped over the support underneath
which I couldn't replicate because I guess my cooling is too good but what it does when
you look at these parts is create a scaffold for the structure above! so that is another thing to
remember if you're stuck with a part like this and don't want to have to increase infill or whatever.
Did I say finally? One more thing then I guess. I thought about the example earlier and wondered
if you could use some creative CAD work to support literally bridging round corners.
This is something I guess is a question really, but I struggled to find a solution.
If we take say a 90 degree curve like this, I can't find a good path or a way to support
that. Same with an S shape, it seems like you could open a can of worms looking into
what can and can't be printed with this kind of layered bridging. With the curve, you could add
some points and bridge to them couldn't you, I guess. And that is a final thought I suppose.
So that was an interesting meander around another part of cura which hopefully will help improve
printing awkward overhanging parts, let me know what you think as always in the comments and
I will see you next time - thank you for watching!