SC QUALITY GUILDSpaghetti diagram
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Place the stations on the layout and enter each route as the stations visited in order. The diagram draws the paths and adds up the distance per day, for the current layout and a proposed one.
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What a spaghetti diagram is for
A spaghetti diagram traces the actual path a person, a part or a document takes through an area. Drawn by hand on a floor plan while following someone through their work, the lines usually end up looking like a plate of spaghetti: crossing, doubling back and covering far more ground than anyone expected. It makes two of the lean wastes visible, motion (people walking and searching) and transportation (moving material).
How to use this tool
- Place the stations. Give each a short code and a position, x across and y down, in feet or meters from one corner. A rough floor plan and a tape measure are enough.
- Enter the routes. List the stations visited in order, exactly as observed, with how many times a day the route is walked. Watch the real work rather than describing the procedure; the extra trips back to a printer or a supervisor's desk are the point.
- Choose how distance is measured. Along the aisles, at right angles, is closer to real walking in most plants and offices. Straight lines understate it.
- Try a new layout. Enter proposed positions for the stations that would move, and compare the daily distance.
Reading the diagram
- Thick lines are legs walked many times a day. The table of longest legs usually shows that a few pairs of stations account for most of the distance. Moving those closer together gives most of the gain.
- Backtracking, a return to a station already visited, usually means the stations are not in process order, or that something needed at one station is kept at another.
- Crossing lines mean people and material get in each other's way.
Convert the distance into time and money: at a walking pace of about 3 miles an hour, each mile walked a day is 20 minutes of someone's shift.
Where it fits
The spaghetti diagram is a Measure-phase tool for seeing the current state, alongside the process map and the value stream map. It pairs naturally with a waste walk and feeds the layout changes that a combination sheet then confirms.
On the exam
The CSSBB lists spaghetti diagrams among the process analysis tools, with value stream maps, process maps and the gemba walk (V.A.2). The CQPA asks candidates to apply lean tools to reduce waste in cost, inventory, labor and distance (II.C.1). Expect to recognize a spaghetti diagram, say which wastes it reveals, and choose it over other process maps when the question is about movement.