Sparse Infill with Stronger Members

[lars86 42]

Hi guys,

I'm wondering if a different style of sparse infill exists in a slicer. I believe that KISSLicer simply does every other line for 50% infill, every third line for 33%, every 4th for 25% etc; and just over extrudes to "interpolate" for values that fall in between.

I'm not sure how Cura handles it.

What I think would be very useful is an option like this:

You could specify the thickness of the members 't' like a shell thickness (increments of nozzle width), and the spacing between members 'S', independently.

The single pass infill normally used is only so strong, but I feel that this would allow for very strong internal ribbing when tuned well for a given part. Does this exist?

[ultiarjan 1,221]

Not sure I understand why you would want this? Lets say in a certain area you now make 20 infill lines of 0.4 you think 10 lines of 0.8 with double the gap in between would be stronger? In general a lower gap in between also helps with easy closing of top layer f.e.

For sure it's good to have options, in the picture below you see the infill options of simplify3D. As far  as I can see you can't set the thickness like you want, but you can over extrude the infill to create thicker infill.

Edited May 2, 2015 by Guest

[lars86 42]

Lets say in a certain area you now make 20 infill lines of 0.4 you think 10 lines of 0.8 with double the gap in between would be stronger?

 

I do.

It's not something I've tested, but call it an engineer's hunch. I think that the cumulative strength of a thicker rib, can be higher than individual strands added up.

[swordriff 119]

Infill strength

I find this a very interesting subject: It is a fact that a solid steel rod bends more easily, than the same diameter steel rod with an axial hole in it (depends on wall thickness, which can not be "zero")! Saves weight.

It is because the core of the bar acts as a leverage for the bending action.

After a solid bar is bent, it is still almost as strong as before (depends a little on the type of steel/material).

When the hollow steel bends, it collapses more, and loses a lot of its stiffness.

After the hollow structure is bent, its designed strength is completely lost and no useful calculation is possible.

[ghostkeeper 105]

With the new infill technique coming up for the next CuraEngine release, there is a new infill method that makes triangles rather than squares. Lars' idea still holds, but it's something to keep in mind because that makes it a bit more complicated.

I think the idea holds some merit, from what I know of static physics. With the same infill density, it could be stronger against certain types of force, specifically a force that is spread out throughout the surface of the object. This is because two beams stuck together will be more resistant to shear and (by extension) bending, while still having the same resistance to compression individually. Of course, the larger gaps will make the centre of these gaps weaker, so it will be weaker against sharp, piercing forces.

This sort of thing requires a lot of testing, because I predict that the thicker ribs could be visible on the outside if the shell is thin, and the bigger gaps could lead to more 'rounding errors' due to the coarser discretisation of the infill (e.g. a small part could get 0% infill because it happens to fall completely within a gap). There is also the matter of exposing too many parameters to the user, though the next Cura release will streamline that somewhat better too.

[lars86 42]

Infill strength

I find this a very interesting subject: It is a fact that a solid steel rod bends more easily, than the same diameter steel rod with an axial hole in it (depends on wall thickness, which can not be "zero")! Saves weight.

It is because the core of the bar acts as a leverage for the bending action.

After a solid bar is bent, it is still almost as strong as before (depends a little on the type of steel/material).

When the hollow steel bends, it collapses more, and loses a lot of its  stiffness.

After the hollow structure is bent, its designed strength is completely lost and no useful calculation is possible.

Swordriff, you are close, but a little off.

For the same diameter bar, solid is both stiffer and stronger than a hollow bar.

For the same weight bar, a hollow will be stiffer than solid because the mass is distributed into areas where the material properties can stiffen the bar. For a given angular deflection, a greater material displacement is required, the further you get from the centerline. So, material very near center doesn't resist bending efficiently.

[lars86 42]

With the new infill technique coming up for the next CuraEngine release, there is a new infill method that makes triangles rather than squares. Lars' idea still holds, but it's something to keep in mind because that makes it a bit more complicated.

I think the idea holds some merit, from what I know of static physics. With the same infill density, it could be stronger against certain types of force, specifically a force that is spread out throughout the surface of the object. This is because two beams stuck together will be more resistant to shear and (by extension) bending, while still having the same resistance to compression individually. Of course, the larger gaps will make the centre of these gaps weaker, so it will be weaker against sharp, piercing forces.

This sort of thing requires a lot of testing, because I predict that the thicker ribs could be visible on the outside if the shell is thin, and the bigger gaps could lead to more 'rounding errors' due to the coarser discretisation of the infill (e.g. a small part could get 0% infill because it happens to fall completely within a gap). There is also the matter of exposing too many parameters to the user, though the next Cura release will streamline that somewhat better too.

You bring up some good points.

It would definitely be an advanced method, where the user would be responsible for sizing the pattern appropriately.

Maybe there could be a checkbox that allowed any cavity equal to or smaller than the grid spacing, to be filled solid.

I like the triangular infill pattern idea, and can't wait to try it out.