Help with Petri Dish Geometry & Boolean Subtract Issue

[lorenero_99]

Hello Sim4Life community,

I'm trying to create a Petri dish model with a liquid solution, but I'm consistently failing with the Boolean Subtract operation.

Goal:
Petri Dish: Outer R=18mm, H=11mm. Needs a 1mm solid bottom and an open top.

Solution: R=17mm, H=10mm. Needs to fill the Petri's cavity, flush with the top edge.

Intended Object Setup (Z-ranges):
Outer Cylinder: Base at Z=0mm, Top at Z=11mm.

Inner Cylinder (for subtraction): Base at Z=1mm, Top at Z=10.9mm (Height=9.9mm).

Solution Cylinder: Base at Z=1mm, Top at Z=11mm.

My Problem:
When performing Boolean > Subtract (selecting Outer Cylinder first, then Inner Cylinder):

The result is either completely empty in 3D space or a flat "disk" (no bowl shape).

This happens despite the Sim4Life tutorial stating the operation subtracts from the first selected object.

Key Questions:
Why does Subtract fail like this (empty/disk)? Is there a common issue with precisely aligned surfaces (e.g., Z=10.9mm vs Z=11mm for cylinder tops)?

[halder]

I recommend checking out the “Multiple Electrode in Homogeneous Medium” tutorial in the LF section. It includes a Petri dish with solution in the modeling part, which is directly relevant.

You're absolutely right about the importance of the Boolean Subtract order. To ensure it works correctly, try the following setup:

(1) Outer Cylinder: Radius = 18 mm, Height = 11 mm, Base at Z = 0 mm
(2) Inner Cylinder: Radius = 17 mm, Height = 10.7 mm, Base at Z = 1 mm (i.e., shifted +1 mm in Z)
(3) Perform Boolean Subtract: Outer minus Inner

This setup should produce the correct bowl shape.