What is the hardest thing you had to build

Question: What is the hardest thing you had to build
- Keywords:
  build,
  hardest thing
Asked by 367heam32 to Fiona on 7 Mar 2018.
- Fiona Freeman answered on 7 Mar 2018:
  
  During my engineering degree we had to machine and build our own industrious lock. We had to do the design and machine the entire lock. I’m not going to lie my blood sweat and tears went into that lock.

Question: What is the hardest thing you had to build