roblox create part grouping model then cframe movement

partA = Instance.new("Part")
partA.Parent = workspace
partB = Instance.new("Part")
partB.Parent = workspace

partA.Name = "partA"
partB.Name = "partB"

local model = Instance.new("Model",workspace)
partA.Parent = model
partB.Parent = model

workspace.maBrickmodel.PrimaryPart = workspace.maBrickmodel.center

while true do
	for i = 1,100 do
		wait()
		workspace.maBrickmodel:SetPrimaryPartCFrame(CFrame.new(workspace.maBrickmodel.PrimaryPart.Position + Vector3.new(0,0,1)))
	end
	wait(.2)

	for i = 1,100 do
		wait()
		workspace.maBrickmodel:SetPrimaryPartCFrame(CFrame.new(workspace.maBrickmodel.PrimaryPart.Position - Vector3.new(0,0,1)))
	end
	wait(.2)
end