Why is lines default pattern for bridging? Wouldnt zigzag be much better??

[rwide 1]

Hi all!

Is there no way of controlling the pattern for bridges when bridging settings are activated? It seems to me that the best setting (in terms of pattern) for bridges is usually zigzag with no walls. This should give great control over the anchoring points..

 

Bridge settings=deactivated

Extra "infill wall count=0

Skin overlap percentage=a reasonable amount

Bottom pattern=zigzag

 

It seems that the only way to achieve this pattern is to deactivate bridge settings, but then i can't control the speed..

 

Am i missing something? 

[Slashee_the_Cow 620]

1 hour ago, rwide said:

Am i missing something? 

I'm going to go with yes (sorry 😞)

 

To bridge a gap, you need lines to go straight from one side to the other, if you try to do a zigzag there'll be zigzag ends in midair that will just fall down straight away.

[rwide 1]

4 hours ago, Slashee_the_Cow said:

I'm going to go with yes (sorry 😞)

 

To bridge a gap, you need lines to go straight from one side to the other, if you try to do a zigzag there'll be zigzag ends in midair that will just fall down straight away.

No. Thats not how it works. If u set a reasonable overlap, the zigzag "ends" will be on top of the inner wall and going in paralell to it for a short distance. This lets you control how strong you want the anchoring points to be..

[Slashee_the_Cow 620]

The walls themselves are bridges and offer no support. Here's the middle of a "bridge" zigzagging:

The inner wall has no support. If you try and make it support weight (like a zigzag line), it will collapse as it has no strength of its own.

 

If you enable bridging, the walls themselves are printed as bridges. Look at how they're printed with a lower flow (thinner lines in the preview):

Those are even less capable of holding up the weight of any lines themselves, which is why the skin is printed as lines, because they're supported by the layer below at the ends:

So they won't add any weight for the walls to support, because if you're bridging a decent distance the line itself has enough weight to droop down (that's why you try and make it set ASAP, which is why you use less flow). Even if the wall has already set by the time you zigzag onto it, a half strength wall cannot support weight on its own.

[rwide 1]

No, you cant always support bridges by the layer bellow at "both ends". Depending on the geometry, sometimes the "bridged walls" has to be used to anchor the crossing lines to. The extra weigh argument seems pretty silly..

[Slashee_the_Cow 620]

Here's another section from the same model which is only supported at one end, which makes it an overhang, not a bridge.

 

With bridge settings on:

 

With bridge settings off:

n.b. This will probably not print without support. Honestly, I don't think I've tried.

 

Notice again how the lines are thinner (less weight). The lines are printed starting on the inside, towards the outside:

This behaviour persists if I set the top/bottom lines pattern to angles that would force lines in an ordinary skin section on that layer to go along the X axis (or at a diagonal), not Y as shown.

 

So it seems counterintuitive, right? The lines should go along the X axis so they're supported at one end and not as long, so they're lighter and don't drag the whole thing down? If they were on a diagonal they'd be longer than lines straight along the X axis which again would be putting more weight on an unsupported line (as well as requiring lines which are supported only by the bridge wall, so no support and added weight), so along the X axis makes sense, right?

 

For starters, these settings are designed for bridges, not overhangs, so they're not designed for this. So why along the Y axis (no pun intended)?

• They start in a supported area and then move outwards.
• The preview in Cura shows the lines as thinner because they have less flow; that doesn't mean they won't end up expanding to touch (and support) one another as they set.
• You're starting by putting the weight as close to the supported area as possible, rather than dragging down the unsupported part by putting weight on it from the start.
• You're preventing diagonal shear by adding weight to one side first, even if you immediately follow by doing the opposite line - which adds travel time when you're already working on as tight a schedule as possible.
• The longer wall at the end is going to be less capable of supporting weight than the short walls, because it's already got the stress of holding itself up.

If you could share a Cura project (.3mf, get it set up then go to File > Save Project) or at least share the model file and point out specific areas where you think a zigzag pattern would give you a better bridging result, I'd be happy to have a look at it. It's even possible that zigzag lines might work better in your situation. But as a general rule, it does it the way it does because it works best in most situations.

[rwide 1]

As if you couldnt have bridging settings activated with zigzag pattern going in the same direction as a line would..

 

Anyways. I don't really care what is default and what is not. It would be great if given the option to choose continous line (zigzag) or normal lines 

 

The main argument for the zigzag pattern would be to eliminate/reduce the risk of anchoring failure at the endpoints of the bridge.. 

[Slashee_the_Cow 620]

You're welcome to submit a feature request for it. But I personally don't think it would work as well as you do.

 

Disclosure: This is my personal opinion. I do not and have never worked for UltiMaker, nor have I ever contributed to the development of Cura, so they may feel differently about it.

[rwide 1]

Thank you for the link! I just submitted a request. 🙂

[rwide 1]

For anybody interested, there is apparently a Cura fork with this functionality here: https://github.com/smartavionics/Cura/releases