getting an entire model to snap to an imaginary grid?

So I'm creating a furniture system for my game but I need the entire model to snap to a grid, I know how to snap just a part to a grid and I tried using that function and a for loop to snap each part to a grid in the model but that made it worse

local tool = script.Parent
local moveEvent
local model = workspace.Chair
function Snap(model)
local Pos=model:GetModelCFrame().p
model:MoveTo(Vector3.new(math.floor(Pos.x),math.floor(Pos.y),math.floor(Pos.z)))
end

tool.Equipped:connect(function(eventMouse)

    eventMouse.TargetFilter = model

    moveEvent = eventMouse.Move:connect(function()
      --  model:MoveTo(eventMouse.Hit.p)
        Snap(model)
    end)
end)

tool.Unequipped:connect(function()
    if moveEvent then
        moveEvent:disconnect()
    end
end)

function onKeyPress(actionName, userInputState, inputObject)
    if userInputState == Enum.UserInputState.Begin then
        rotateMod(model, CFrame.Angles(0,math.rad(90),0))
    end
end

game.ContextActionService:BindAction("keyPress", onKeyPress, false, Enum.KeyCode.R)

function rotateMod(mod,rotation)
    local center = mod:GetModelCFrame()
    local parts ={}
    local function scan(parent)
        for _,obj in pairs(parent:GetChildren()) do
            if (obj:IsA("BasePart")) then
                table.insert(parts,obj)
            end
            scan(obj)
        end
    end
    scan(mod)
    for _,part in pairs(parts) do
        part.CFrame = (center*rotation*(center:inverse()*part.CFrame))
    end
end

17:04:14.698 - Unable to cast double to Vector3 17:04:14.699 - Stack Begin 17:04:14.701 - Script 'Players.Player1.Backpack.Place Chair.Placement', Line 6 - global Snap 17:04:14.701 - Script 'Players.Player1.Backpack.Place Chair.Placement', Line 15 17:04:14.702 - Stack End