Origin Axis challange

Lesson 2 A How to Modeling Skills Building Exercise

This by the way, is probably the most difficult piece of geometry I have ever done and one of the best examples of the OAM methodology.

This example utilizes a pin arrangement which, as designed would result in a final assembly that would be inseparable upon completion. However, there are aspects of this design that lead me to question how tight the final fit would be.

Objective: mechanically assemble a hollow sphere

Requirements and Instructions to get started:


  • Utilize the inherit origin plain's and axis that are provided in the native file of your CAD software. Every sketch used to build the part must directly or indirectly reference the origin, plain's or axis. Every part must utilize the origin, plains or axis for the assembly process.

  • Robust design: The model must be scale-able. This will demonstrate the robustness of the model when changes are made to the model. Method Suggestions: skeleton modeling, parametric associations.

  • Mechanical means of assembly using pins, screws or other means of assembly such that when completed the results would have a high probability of providing a tight fitting assembly that would not fall part and may be constructed in such a way that once completed, might not be able to be disassembled with out being destroyed.

Instructions to start:

  • Plan out how you will control the size of the sphere using skeleton techniques or other means as suggested above. For more on skeleton modeling click here.

  • Create a hollow sphere and section it into 8 parts.

  • Remember, the edges of the resultant parts will need to be trimmed to allow the sphere to be re-assembled such that the exterior and interior surfaces are tangent and do not create an interference. Key to this is to follow the contour of the sphere in X, Y and Z.

  • See the examples shown.

  • Also a good thing to remember here is the 3 points of contact rule.

    • 3 points of contact make a plane... 4 points makes a problem.