Player spawns in the sky when a model is welded to it?

Alright, so I'm trying to weld a model to the player's left arm. The weld is successful, but they for some reason spawn in the sky. I'm pretty sure it has to do with the game thinking the parts in the model are the floor, so it tries to spawn the player higher up than it's supposed to be. This is REALLY high up. ! (That's the baseplate down there)

I tried adding a wait() function to the script, so it welds later, but it just breaks it completely!

I really hope I'm not missing something that should be really obvious, but if there's anything wrong with my code, please let me know so I can fix it. Dear god, this is annoying.

game.Players.PlayerAdded:Connect(function(plr)
    plr.CharacterAdded:Connect(function(chr)
        local part = chr:WaitForChild("Left Arm")
        local ummweldthing = workspace.coolthing:Clone()
        local weld = Instance.new("Weld", chr)
        weld.Part0 = part
        weld.Part1 = watch.primarypart
        weld.C0 = part.CFrame:inverse()
        weld.C1 = part.CFrame:inverse()
        ummweldthing.Parent = workspace
        ummweldthing:MoveTo(chr:WaitForChild("Left Arm").Position)
    end)
end)

I've even tried setting the player's position to somewhere else, nothing's working.

Please help!