Problems when splitting closed mesh

(Chgehrig) #1

here’s the following:

i would like to print a mold for shoe lasts. i have a mesh of a last. my goal is to have a streamlined process where i can make alterations to the last, then print out the mold in two parts (so it fits onto my 3d printer) for casting the last in resin. the mold will be destroyed by taking out the last.

the idea is to split the mesh in two, then use the mesh offset command to create the mold. however, if i split it in two, i (obviously) get a lot of naked edges (428, in fact. this is too much to close by hand, especially if i want to streamline the process). there a way of splitting meshes without creating naked edges?

  1. if not, how are these edges best patched?

  2. could it be that i’m doing the whole thing wrong by using a mesh in the first place? should i just turn the whole mesh into nurbs?

these are very newbie questions, i just started out with rhino. any help would be appreciated



(Dan Belcher) #2

It’s always helpful to post a model so people can take a look to see where you might be having trouble.

(Chgehrig) #3

alright, i will do that later this week. i’m still trying out the meshtonurb to see if i can solve it

(Chgehrig) #4

so i have actually managed to get something close to what i had in mind: i split the mesh and created a kind of shell. however, i have trouble with the offset mesh command; i would like to achieve a straight rim, like in the video here. this needs to happen a) so it can lay flat on the print bed and b) so i can reattach the two pieces to form a mold. however, when i offset my mesh, the rim offsets differently. why does that happen? is there an easy fix? i exaggerated the offset so the problem is more easily recognisable.last.3dm (4.7 MB)

(Pascal Golay) #6

Hello - the offsetter is doing it right, as far as I can see - the problem for you is the offset of that edge(s) along the face normals does not make a planar edge -that is expected. The way to do this is to offset the mesh when it is all one piece, and then split the mesh and fill in the gap between inner and outer.


(Chgehrig) #8

thank you very much pascal, i think i managed to do it. here’s my workflow, maybe there are ways of optimizing it?

  1. adjust last
  2. offset mesh
  3. split mesh
  4. extract hole boundary from inner & outer shell
  5. planarsrf of the two curves created in 4.
  6. convert this to mesh
  7. join to mesh
  8. match mesh edges

i then used unify normals and align mesh vertices on the whole thing, mainly because when in checked there were a lot of issues. then i repeated these steps for the other half. i also created a hole in the other half (similar process by splitting mesh with a cylinder, then use loft on the curves created from extract hole boundary). the whole thing is printing right now, so far it looks good. thanks again, i really learned a lot.lastnew.3dm (5.0 MB)