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)?