Weld arm forward without breaking joints?

I made a sword using a hopperbin (i dislike tools) and i wasn't sure about how people make the arms stay still, they don't just offset the shoulder joints because the arm actually stays still. I saw a few free models where it used welds. (but i can't find them again :c) What im doing is;

local weld;


local function WeldArm()
    print("weldd")
    weld = Instance.new("Weld")
    weld.Parent = char.Torso
    weld.Part0 = char.Torso
    weld.Part1 = char["Right Arm"]
    weld.C0 = CFrame.new(1.5,0,-0.5) * CFrame.Angles(math.pi/4,0,0)
end

local function FixArm()
    weld.Part0 = nil
    weld.Part1 = nil
end

This just freezes my arm in one location after i use FixArm(). How can i successfully weld body parts into certain positions and be able to fix it later, and not just for arms? Thanks for any help.