How thick should the thinnest wall in the mold be set to ensure the hardness?

At half, the gap between the two frames should not be less than half the depth of the frames and not less than 8mm.

If the toughness of the material is good, it can reach 1/3.

In addition, the bottom and corners of the frame should try to avoid acute or right-angle transition, and it is best to make rounded corners or R angles.