Redditor /u/ViAlexis has found a way to make your life a whole lot easier if you have the patience to follow their instructions.
1) Go to this area on the map.
2) You need to find the mayoral building, pictured below. Go into the basement (the stairs are on the left). You will have to pick a door lock that may be either advanced or expert level.
3) Travel down the below hallway, which will be lit up – you’re going to have to disarm all of these and try not to activate the three turrets. Quicksaving is probably a good idea. If you set off any of them you’ll have to start over.
4) This is what the above hallway will also look like with all of the sensors activated. Press the big red button on the right, which will open the door. When you press it a second time, the door closes and all of the lasers re-arm. You’ll have to disarm these and you can go through the hallway again and collect fiber optics, crystal, and steel.
5) Rinse and repeat as many times as you want. We told you there would be patience involved!
If you have Dogmeat traveling with you, this may be a good one to let him sit out.
If you liked this post, check out some of our Fallout 4 gameplay guides: increasing inventory space, changing your field of view, skipping the intro video, unlocking frame rate, which settings to turn on or off, basic and advanced console commands, and disabling mouse acceleration.