You can use IsoCutMesh to cut a mesh, giving open edges, and this takes any field as an input, so it can be any shape you define as a field, including an input mesh
You can also shell a surface and use Isopod boolean intersection with any other field to get a solid fitting a shape (only meshing once at the end).
trimming_v_shelling.gh (249.9 KB)
What we want to avoid wherever possible is generating an isomesh from a field, then using that resulting dense mesh to define another field to be used in another isomeshing component, as it will lose accuracy and be much much slower than if we can do all our operations with fields before a single isomeshing step.
(Sometimes this field-to-mesh-to-field workflow is a useful fallback as a way of turning a non-SDF field into an SDF, but it makes things a lot heavier to process, so shouldn’t be a first choice)
For the specific case of the helicoid fields, it does look like things need to be done a little differently, as they are very non-distance like. I’ll try and make another example for these.