This Chronological Engine is the hero prop I did during my intermediate-term at Think Tank Online.
I really dig into steampunk stuff so I couldn't resist once I saw the model on steamhead.co.uk
I used Maya for modeling the low poly, Zbrush for the high poly, substance painter for baking and texturing, and marmoset 4 for presentation.
The biggest challenge I faced during the process was trying to maintain the roundness of the object without went too high on polys. I managed to stay on 20k tris at the end.