But what would it be called?
Crafting a metal armor and crafting an anti-material rifle and crafting a plasma repeater are very very different.
Calling it "Crafting" would also interfer with Medicine, Science/Chemistry, Survival and Explosives skills as they have craftable items as well.
Rename Repair into Mechanics, making it about figuring out how mechanics work, how to fix them and how to create new ones from scratch.
Make Armorer it's own skill so we can craft, maintain and modify armors. (Crafting armors cost less and they are better, you could also modify armors by adding additional materials to them, like adding Fire Gecko Skin to a Combat Armor to give it +15% fire resistance. (With each armor having 4 slots of modification possible. (You can still repair any and all armors with 7 in Armorer, it just means that you will get a really low bonus to it's CND, making NPC Armorers a more viable choice for non Armorer player characters, but also more costly)))
And have Electronics be the skill for repairing, maintaining and mofifying Energy Weapons of all kinds. (Electronics can also be used for other things, like recharging drained cells, crafting plasma and pulse grenades and tapping out energy sources for Small Energy Cells (That can later be converted to Microfusion or Electron Charge Package))
I think that would be the best set-up if we are to be able to craft weapons and armors.
You aren't forced to take any of these, you can buy a Metal Armor from an NPC, but it will cost more.
You can upgrade said Metal Armor at an NPC, but it will cost more.
You can repair said Upgraded Metal Armor at an NPC, but it will cost more.
Same with the other things.
Each skill serves three purposes:
1. crafting items from scratch, which can be sold for a lot more than the parts on their individual value.
2. Repairing items more successfully.
3. And modifying their statistics, which makes the armors better than the vanilla counterpart.
All three services that these skills provide can be bought from NPC's, so it doesn't exclude anyone, but these services cost a lot, especially for the really good stuff. (Ever tried to repair an elite weapon in New Vegas by an NPC? It costs a fortune, up to 6.000 caps and sometimes even more.)
"But where does crafting bullets fit in then?"
I think Explosives should do fine.
Again, you can buy the craftable ammo from NPC's, so not picking Explosives doesn't mean you can't get Incendiary Anti-Material Rounds, it will just cost you a lot more.
So if you pick Guns and don't pick Explosives, Armorer or Mechanics, then don't fret, you can still get great stuff, you just need to pay more for it.
Maybe Barter would be a good idea for that character. (Could make Barter more useful actually if we're more inclined to start using NPC services.)
Electronics and Mechanics have more uses than Armorer though, both theses skills work their way into other areas of the game as well, like for example: Using Electronics to fix Caesar's Auto-Doc, or using Mechanics to sabotage that huge gun at the presidential speech at Hoover Dam.
Armorer has less uses in that regard, but it's still a very useful skill, hell, a crafted Deatchlaw Skin Reinforced Combat Armor MK III is going to protect you so well you could almost take on Arizona on your own.
Not saying my system is perfect. (Though I think it's pretty damn good)
But "if" we are going to be able to craft armors and weapons from scratch then I don't see how "Repair" fits into it, and an overall Crafting skill just simplifies everything too much, making NPC's' services even more obsolete than they already are.
Just my 2 cents.
But I'd rather not be able to craft armors or weapons if it's gonna be tossed into "Repair" or "Science" or "Crafting".
New skills or nothing, that's what I suggest.