If you ever read the Tom Clancey book "The Sum Of All Fears" it shows you how easily you can put a nuclear weapon together as long as you had the refined weapons grade uranium or plutonium.

Using just the equipment found in a eyeglass manufacturing is the exact same precision you need to craft the components of the bomb and trigger hand that crushes the plutonium at a fast rate quick enough to set off the chain reaction.
The trigger is set into motion using a conventional explosive aimed into a cone btw that starts the trigger process that leads to the chain reaction of atoms.