Price is often the first thing buyers look at when choosing a tool. Yet the real driver of a part’s cost is the time the machine spends on it. In this article we calculate the cost per part with a simple formula and compare two tools with numbers.
What makes up the cost per part
- Machine cost: Machine hourly rate (depreciation, energy, operator, maintenance, overheads) × cycle time.
- Tool cost: Tool price ÷ number of parts machined during the tool’s life.
- Tool change cost: Machine downtime to change the tool ÷ tool life.
- Scrap and rework: The share of out-of-tolerance parts.
+ (Tool price ÷ tool life)
+ (Machine rate per min × tool change time ÷ tool life)
A worked example
Let’s compare two end mills on a machining centre with a rate of 1,200 TL per hour, i.e. 20 TL per minute. Tool change time is 3 minutes for both.
| Tool A | Tool B | |
|---|---|---|
| Tool price | 1,000 TL | 1,600 TL |
| Tool life | 200 parts | 300 parts |
| Cycle time | 4.0 min | 3.4 min |
| Machine cost / part | 80.00 TL | 68.00 TL |
| Tool cost / part | 5.00 TL | 5.33 TL |
| Tool change / part | 0.30 TL | 0.20 TL |
| Total / part | 85.30 TL | 73.53 TL |
Although Tool B costs sixty percent more, it saves about 11.8 TL per part. For a line making 10,000 parts a year, that is roughly 118,000 TL. And in both cases the tool accounts for less than seven percent of the total.
Hidden costs that are often missed
- Unplanned stops: A broken tool stops the machine longer than planned and may scrap the part.
- Quality control: Inconsistent tool life forces the operator to measure more often.
- Extra operations: Deburring or a second setup lengthen total time. See our article on angle heads and single-setup machining.
- Stock and supply: A tool that arrives late can cost more than the most expensive tool.
Measure to decide
- Record cycle time and tool life (in parts) with the current tool.
- Trial the new tool on the same part with the same criteria.
- Define the tool change criterion in advance: wear, surface finish or dimensional drift.
- Compare the results with the formula above.
At Mentor Mühendislik we report cycle time and tool life comparisons from trials on your machine using this method. Our carbide drilling guide shows with a concrete example how cutting data affects cycle time.
