But I thought it was very, very tricky to “smash” the component together with the right force... just touching them is enough?
You are talking about the uranium “gun weapon”. It is not tricky at all to get them together. Actually, this is rather easy method.We dropped a uranium gun weapon on Hiroshima.Many nations uses the gun weapon for artillery shells(See Shot Grabel/Operation Knothole) The North Koreans have been producing the tricky plutonium implosion bomb and recently they switched to the uranium “gun” method because it was cheaper and much easier.
The scientists did not test the “gun” design because they were confident it was going to work. But, they needed to test the implosion method because they were not sure it was going to work. Well, it worked.