What happens to extra materials from salvaged junk?

Question

So I have read through multiple questions about how the workshop handles the various categories when it automatically scraps things to produce raw materials for projects that you are building. It has been clearly shown that anything outside of the "junk" category is safe from automatic salvage.

However, I wanted to know what happens to things in the "junk" category when they are salvaged. If something from junk gets automatically dismantled to supply some material for a project, but the project only requires one of the several pieces of material from that broken down junk, do you still get the left-over materials or are those used up as well? I know that if you manually break down junk items yourself (i.e. drop them on the ground and use the settlement interface to break them down) then all of the materials are stored in your workbench, but what happens to those materials when the pieces are broken down automatically?

Answer 1

In researching the related question How can I break items down into their components, I saw a complaint on Reddit to the effect that the extra, leftover materials get destroyed.

Why this is a common belief

Many people seem to believe this, and there's a good reason for that: it's confusing. And it's confusing for two reasons:

1. The composite item is removed from your character's inventory, but the leftover components are placed in the Workshop's inventory.
2. There's sometimes a delay before the leftover components reappear. If you want to speed up the process: go into Workshop mode, try to build something, and then exit. This appears to force the Workshop to update its inventory contents list.

Go, science!

I settled the question with science. I've tested this with various items a dozen or so times using the Armor Workbench, the Weapons Workbench, and the Workshop crafting menu.

The leftover components have always (so far) appeared in the Workshop inventory, but there's sometimes a delay.

Here's one of the experiments:

Experiment

• Remove all Lead from your inventory and the Workshop's inventory.
• Add two pencils to your inventory; each pencil has 1 Lead and 1 Wood.
• Go into the Wood Structure crafting menu—not to craft anything but just to check your Wood component count.
• Craft a Radiation Emitter, which among other things requires 2 Lead.

By creating the Emitter, we force the Workbench to dismantle the pencils, which liberates 2 Wood and 2 Lead.

If our Wood component count goes down, wood has been lost/destroyed. If it stays the same, our 2 "potential" units of Wood have simply been converted into 2 actual units of Wood.

Result

Our Wood component count remains unchanged. So unneeded materials are retained, just as though you'd broken the item down yourself.

Answer 2

The same thing happens with those materials, you do not lose anything from what I can tell.

For example (I'm making up exact components/amounts for simplicity), say you want to build Fisto (not actually in FO4, as far as we know, I just like that robot) and only have all required Fisto components except for a screw in your materials. Suppose manually breaking down a cabinet yields:

• Wood(4)
• Steel(2)
• Screws(2)

Assume you only need 1 more screw for your Fisto and only a cabinet is in your junk to be scrapped. You build your item and now your materials should be:

• Wood(4)
• Steel(2)
• Screws(1)

And of course there is no more cabinet.

Answer 3

If the item is in your inventory then it will put the extra parts into the nearest workshop as well. I just got finished doing the experiment by taking one component out of my workshop, putting it into a regular container, then made something that needs the component but the the rest of the parts to the junk item I had in my inventory. I've only tested it with junk so far and I don't expect it will auto-scrap anything else in your inventory, at least I hope it wouldn't!