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I am new to 3D printing, and new to mold design.

I played around with a model from Windows Paint 3D library: enter image description here

And I realized that it would not be easy to 3D print a mold out of this.

First of all I focused on the legs, and the fact that I cannot get the 4 legs by just splitting the negative shape into two mold parts.

Then I realized that maybe a zigzag cut could help, but it only work for legs when they are not parallel to each other, unlike the back legs.

And in fact, there is the same problem for the ears.

I'd like to point out that I want to mold paper pulp, so I cannot really do injection molding, which means I really need access to the entire figure from both parts of the mold.

It really seems like it is an impossible problem.

Are there tricks?

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  • $\begingroup$ Hi and welcome to 3DPrinting.SE! As the mold is projected to be created from paper pulp, what is the connection to 3D printing? $\endgroup$ – 0scar May 24 at 18:42
  • $\begingroup$ @0scar As I read it, the (preferably 3D printed) mold will be used to form paper pulp. Biodegradable scatter items, perhaps? $\endgroup$ – Zeiss Ikon May 25 at 11:52
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In traditional mold making, this would require a "sectional" mold -- one that breaks into mutiple pieces to free the legs, rather than just two halves. Sometimes you can use a non-planar mold break line to avoid this issue; look at the molds made for casting miniatures that aren't neatly arranged to see examples, but as you note, with one rear leg alongside the other, the narrow space between isn't accessible with a rigid mold and a molded figure that can't be flexed.

One way around this would be to print the figure and make a flexible mold from it -- the mold wouldn't be printed, but would be molded from a positive figure. That would let you use a flexible mold material to run a join between the rear legs and still separate the mold, with a little care. You may also want to make the mold in layers, as would be done for denture making -- using a soft, highly flexible material such as the alginate used in denture making for direct contact with the original figure, and then reinforcing the very soft contact layer with a sturdier backup layer to provide support.

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    $\begingroup$ There are brush-on silicone compounds that would fit your description and your methodology is sound. $\endgroup$ – fred_dot_u May 24 at 13:56

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