Short answer
The cost of a breakdown is not the part price written on the invoice. When a machine stops, the operator waits, other crews on site wait, the programme slips and on some contracts delay penalties start. Add those lines up and the number is usually many times the part itself. Until downtime is calculated, purchasing decisions are made on the wrong axis: the cheapest part gets chosen, when what should be sought is the fastest solution.
What downtime is made of
- The idle machine: every hour it is not producing a return is a cost; if hired, the rental keeps running.
- The idle operator and crew: labour cost does not stop, production does.
- Chain waiting: when the breaker stops, the loader and trucks wait too; one machine stopping can stop several crews.
- Programme slip: on a tight schedule the delay pushes later stages and on some contracts creates penalties.
- Emergency supply premium: sourcing a part urgently costs more in freight and price than normal supply.
- The cost of a workaround: carrying on with the wrong part or an incomplete repair usually produces a second failure.
Calculate your own downtime cost
The calculation is not complex: work out once what an hour of downtime on a machine costs you. Add machine depreciation or rental, operator cost, the cost of other crews waiting, and the hourly share of any daily production target.
Once you have that number, purchasing decisions change. If the premium for getting a part a day earlier is below the cost of a day of downtime, you pay it; if it is above, you do not. The decision moves from instinct to arithmetic.
The same number also settles the critical spares decision directly: if the cost of holding a part in stock is lower than the downtime its absence would cause, you hold it.
The cheapest part can be the most expensive decision
When price is the only criterion, a part with a long lead time or doubtful compatibility gets chosen. The amount saved on the part stays far below the cost of two extra days of the machine waiting. The comparison should not be between part prices but between total times to solution.
Practices that shorten downtime
- Speed up diagnosis: a check sequence that starts from the symptom removes the hours lost to trial and error.
- Hold critical parts in stock: which parts count as critical is covered in a separate guide.
- Keep model and serial number records to hand: the biggest time loss in a parts request is establishing which model needs which part.
- Standardise attachments: equipment sharing the same parts reduces stock lines and shortens supply time.
- Keep a failure log: repeat failures only become visible with records, and the root cause is only solved then.
What record-keeping returns
Which machine, when, which part, how many hours of downtime. That simple four-column record makes three things possible at once.
First, root cause analysis: the same part being replaced repeatedly shows the problem is not that part but something else destroying it. Second, the stock decision: which part is genuinely critical is determined from history rather than guesswork. Third, pricing: when quoting a new project you can put a realistic maintenance cost into the figure.
This record needs no complex system; a single sheet in the machine file is enough. Complex systems do not get maintained, simple records do.