Setting up a brim/raft for only a portion of the overall print

Question

I'm trying to build an assembly with one larger part (about 50 mm x 50 mm), two small parts (about 10 mm x 5 mm) each, and one part that starts with two 2 mm x 2 mm squares that eventually bridge into a sort of flap. The larger part has decent adhesion for a couple of layers, but the small parts are slipping off the table right away and the nozzle drags them onto the large part since it's the last part being printed in the group, resulting in some stringing.

My bed is adequately leveled and can print larger models well so my suspicion is that the small parts are too small for good bed adhesion and need a brim or a raft to increase the surface area. Is this correct? If so, is there a way in Cura to add a brim or raft to the small parts and not the large part? Ideally I would print all pieces at once instead of the large part separate since I will be doing batches of these assemblies in the future.

I'm using Ultimaker Cura 3.6, printing with PLA filament set to 200 °C at nozzle and 60 °C on the bed.

Answer 1

This is a "No" and "Yes" answer, it depends on the version of Cura you are using!

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No, there are no options available to set the brim to some of the parts in Ultimaker Cura (at the time of writing this answer, pre Cura 4.5.0). You could however change the smaller model to include the brim in your design, or add so-called "Mouse Ears".

At the time of writing this answer, the image below shows the Ultimaker Cura interface for "per model" settings, basically different settings with respect to the other models. As can be seen, you cannot expand the Build Plate Adhesion (it already shows the arrow downwards, so expanded):

But, yes as of Cura 4.5.0 (see this answer) the "per model" settings have changed and the Build Plate Adhesion is added with the option to add a Brim Distance to trick Cura into de-attaching the brim (it will print a brim, but it is not attached to the part):

When applied to several models this could result in models with a brim attached and others without the brim attached:

Answer 2

In the newest version of Cura (4.5.0), in the per model settings, the only thing you can change for options set Build Plate Adhesion is Brim Distance. What this allows you to do however is create a brim for everything with the distance of a millimeter or two, and then for the part that needs the brim, you just set the distance to zero in the individual part settings. It's a little janky, but you essentially create a skirt for the parts that don't need a brim.

Answer 3

This post is quite old, but I describe how I solved this for anyone has the same problem I had: areas moved by the nozzle as the base of some appendices are too thin and tall.

In Cura 4.8 (I don't know since which version this feature is available) it is possible to add some custom shapes (cubes or cylinders) to your model. You can find this tool after move, resize, etc,, in the prepare page (left side icons).

So you can add some custom supports to protect from falling/moving some areas of a single model that need to be kept in place. These added parts can be moved and resized as you would do with the any other imported model.

I found this very useful to avoid that the nozzle moves parts with a small base area that are connected to the rest of the model on a higher level and the lower part is not stable enough. Especially when printing TPU or other flexible filaments.