Custom Support on Cura 4.3

[B_Terneyre 0]

Hi,

 

My company has recently bought an UM3 and used its dual extrusion abilities extensively, but the auto-generated supports in Cura have been curious to say the least. Here are the parts we have been printing:

 

 

These were developped on Solidworks and dragged in Cura as .STL files. They are perfectly symmetrical, (as in, I have used the mirror functions on Solidworks, which means that each time I modify the original file, the mirrored piece updates automatically to remain symmetrical) but the supports in Cura are not:

 

Front:

 

Back:

 

 

Left:

 

 

Right:

 

 

Cura generates supports on what are essentially vertical walls, i.e. some of the corners of the piece on the front view, and on a part of the exterior wall, but only on the piece on the right, oddly enough. We are using Cura 4.3 and default support parameters. We have tried to tweak some of the parameters but the only significant changes come when modifying the overhang angle. The pictures you see are with said angle set to 45°, we do not want to increase it because we want to keep it on the essential parts, and lowering it adds even more unnecessary support on vertical walls.

 

Point is, we are not satisfied with the automatic supports on Cura and we would like to create custom supports to not waste printing time and material. We want to make our own supports on our CAD design, but we also want the support to be in PVA. Is there any way to assign different materials to specific parts of the same model on Cura, or should we make a separate .STL file for the support and merge it with our piece on Cura?

[ahoeben 1,948]

You can try lowering the Support Horizontal Expansion setting.

 

The STL format does not support multiple separate bodies in a single file. Other formats such as 3mf do. If your CAD software exports 3MF files, that might be an option to load your custom supports and print them as support using the "Per Model Settings" tool.

[B_Terneyre 0]

25 minutes ago, ahoeben said:

You can try lowering the Support Horizontal Expansion setting.

 

Thanks for the tip, lowering the horizontal expansion to 0mm actually removes all the vertical unnecessary supports, so I guess we won't need to customize our own support in this case.

 

Although I have to ask: is this recommended? I understand that a higher horizontal expansion makes the support sturdier, but is it necessary on parts that already support themselves?

[ahoeben 1,948]

It is not necessary on all parts. It does improve stability on some parts.

[geert_2 557]

An option you could consider is to design part of the supports in CAD, in the same material as the model. And make these as efficient as possible, and as sturdy as required. But leave a gap between the support structure and the real model, don't connect them. And then let Cura fill-in that gap with its automatic supports. You could design a dove-tail on your own supports, so that Cura's PVA gets a good mechanical grip on your custom support.

 

I am not sure if this would work well (I only have single nozzle UM2-printers), but it might be worth trying?

 

Anyway, I usually design custom supports for all my models that require support, and I design-in features to make the support stable enough and make removal easier in hard to reach areas (e.g.: extensions to grip the support with pliers, or holes to insert pulling-hooks, etc.).

 

[B_Terneyre 0]

17 hours ago, ahoeben said:

It is not necessary on all parts. It does improve stability on some parts.

 

Do you have examples of parts where it would be necessary? Small or big pieces? Cylindrical, square or oblong geometries, etc...?

 

From what I understand, the main point of a support is to "carry" the higher angles of overhangs during printing, so I don't really see in which cases I would need a horizontal expansion

Edited November 15, 2019 by B_Terneyre

[johnse 31]

I think it is in cases where one or more edges of your model print on top of the edge of support. For example, an overhang, or a long bridge. Support is meant to bond weakly to the primary material, so if you try to print right at the edge it can sometimes cause problems.
 

in your case above, most of the support was surrounded by walls.