Player dies after equipping weapon 3 times after adding this script?

I am attempting to make realistic arms for my gun. I could have added this to the rest of my script but I am lazy and my other script is quite a mess.

I added this script to make the head look up and down, therefore, moving the fake arms in the direction of the camera.

When you equip the weapon 3 time the player dies. It is erroring on line 15 saying that I am attempting to index global kneck a nil value.

local tool = script.Parent
local equipped = false
local weld = Instance.new("Weld")

function equip()
	player = game.Players:GetPlayerFromCharacter(tool.Parent)
	local torso = tool.Parent:FindFirstChild("Torso")
	local HCF = tool.Parent.Head.CFrame
	head = tool.Parent:FindFirstChild("Head")
	kneck = torso:FindFirstChild("Kneck")
	local equipped = true
	weld.Parent = torso
	weld.Part0 = torso
	weld.Part1 = head
	kneck.Part1 = nil
end

function unequip()
	equipped = false
	weld.Parent = nil
	kneck.Part1 = head
end

while equipped == true do
	wait()
	weld.C1 = player.CurrentCamera.CFrame.lookVector -- This is not working either so any additional help here would be a nice bonus.
end

tool.Equipped:connect(equip)
tool.Unequipped:connect(unequip)