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- Cutting speed and feed - what each parameter controls, and the symptoms that identify which one is wrong
- Tool cost per part - the four components of true tool cost, and why the cheapest insert frequently costs the most
What each parameter controls
Confusing the two is the source of most parameter problems, because they respond to different symptoms.
| Parameter | Governs | Raise it when |
|---|---|---|
| Cutting speed | Edge temperature, coating performance, wear rate | The material is soft and the tool is not wearing, or built-up edge is forming |
| Feed per tooth | Chip thickness, whether the edge cuts or rubs, chip breaking | The edge rubs, work-hardens the material, or the chip will not break |
| Depth of cut | Load on the tool, number of passes, vibration risk | Fewer passes are needed and the setup is rigid enough |
Why cost per part is not cost per insert
Tool purchase cost is usually the smallest part of the total. Cycle time and unplanned downtime dominate, and a tool that costs less but runs slower or fails unpredictably moves both in the wrong direction.
The numbers worth recording are parts per edge, cycle time per part, whether each tool was changed on schedule or after a failure, and any scrap attributable to the operation. Those four make a comparison on total cost rather than on price.
In this group
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Cutting Speed and Feed
Cutting speed is the surface speed of the tool against the material and it decides edge temperature, so it is set from the workpiece material. Feed per tooth is the chip...
Read moreTool Cost per Part
True tool cost is the tool price divided by the number of usable edges and the parts each edge produces, plus the cost of the time spent changing it and the cost of the...
Read moreFrequently asked questions
What is the difference between cutting speed and feed rate?
Cutting speed is the surface speed between tool and material and it sets the edge temperature, so it is chosen from the workpiece material. Feed rate is how fast the tool advances and it sets chip thickness, which decides whether the edge cuts cleanly or rubs.
What happens if the feed is too low?
The edge rubs instead of cutting, because the chip thickness falls below the edge radius. That generates heat, work-hardens the surface in stainless and similar materials, and wears the tool faster than a heavier feed would.
How do I work out tool cost per part?
Divide the tool price by the parts it produces, then add the cost of the time spent changing edges and the cost of any scrap attributable to the tool. In most operations the purchase price is five to fifteen percent of that total.
Why does the cheapest tool often cost the most?
Because cycle time and downtime dominate the total. A tool that allows a higher feed rate reduces machine time on every part, and that saving normally exceeds the entire price difference between two tools.
Where are the largest gains usually found?
In using the correct tool rather than a cheaper one, because the parameters a tool can support determine cycle time. The second largest is usually runout, since a tool running out of true loses a substantial part of its life regardless of its grade.