Why is my part moving in somewhat random directions when I change only the Y?

Hi, I'm making an expandable shield script that is held on the players left hand. When trying to make it extend however, the outermost piece moves in a somewhat random direction relative to the innermost part of the shield.

remoteevent.OnServerEvent:Connect(function(player, hasgear)
    print(player, hasgear)
    if hasgear == false then
        local gear = shieldgroup:clone()
            gear.Handle.CFrame = workspace:WaitForChild(player.Name)["Left Arm"].CFrame * CFrame.new(-0.20616293, -0.415015221, -0.040222168, 1, 0, 0, 0, 0.999999881, 0, 0, 0, 1)
            gear.par2.CFrame = gear.Handle.CFrame * CFrame.new(0.539999008, 0.160001278, 0, 1, 0, 0, 0, -1, 0, 0, 0, -1)
            gear.Parent = player.Character
        local weld = Instance.new("Weld")
            weld.Part0 = gear.Handle
            weld.C0 = gear.Handle.CFrame:Inverse()
            weld.Part1 = game.Workspace[player.Name]["Left Arm"]
            weld.C1 = game.Workspace[player.Name]["Left Arm"].CFrame:Inverse()
            weld.Parent = gear.Handle
        weld2 = Instance.new("Weld")
            weld2.Part0 = gear.par2
            weld2.C0 = gear.Handle.CFrame:Inverse()
            weld2.Part1 = gear.Handle
            weld2.C1 = gear.par2.CFrame:Inverse()
            weld2.Parent = gear.par2
    end
end)
rme2 = game.Workspace.Part.RemoteEvent2
rme2.OnServerEvent:Connect(function()
    for i = 0,.4,.04 do wait()
            weld2.C0 = weld2.C0 * CFrame.new(0,i,0)
    end
end)

Starting position

After being extended

It doesnt always extend in the same direction, but rarely goes straight up relative to the inner part. What am I doing wrong, how can I fix it?