DefinitionFeed rate is the speed at which a cutting tool advances through the workpiece, usually given in inches or millimeters per minute.
Explained
Feed rate is the speed at which a cutting tool advances through the workpiece. In milling it is calculated as spindle speed × number of teeth × chip load per tooth. It is different from spindle speed, which is how fast the tool rotates, measured in revolutions per minute (rpm).
Feed Rate vs Spindle Speed vs Cutting Speed
Four related values are set for every cut:
| Term | What it measures | Units | How it is set |
|---|---|---|---|
| Cutting (surface) speed | How fast the cutting edge passes the material | ft/min (SFM) or m/min | From tables for the tool and work material |
| Spindle speed | How fast the tool or part rotates | rpm | Calculated from cutting speed and diameter |
| Chip load (feed per tooth) | Thickness of material each cutting edge removes | in/tooth or mm/tooth | From tables for the tool, material and cut |
| Feed rate | How fast the tool advances through the part | in/min (IPM) or mm/min | Spindle speed × teeth × chip load |
On a lathe or drill, feed is usually given per revolution (in/rev or mm/rev), and the feed rate is spindle speed × feed per revolution.
How to Calculate Feed Rate
First find spindle speed from the recommended cutting speed V and tool diameter D:
- Imperial: rpm = 12 × V (ft/min) ÷ (π × D in inches), often rounded to V × 4 ÷ D
- Metric: rpm = 1,000 × V (m/min) ÷ (π × D in mm)
Then calculate feed rate:
Feed rate = rpm × number of teeth × chip load
What Happens If the Feed Rate Is Wrong?
- Too high: each tooth takes too thick a chip, cutting forces rise, finish and accuracy suffer, and the tool may chip or break.
- Too low: the job takes longer than necessary.
- Roughing vs finishing: roughing uses lower speed and heavier feed to remove metal quickly; finishing uses finer feeds and higher speeds for a better surface.
- Chatter: if the cut vibrates, a common first fix is to lower speed and raise feed.
Use lower feeds for small or fragile cutters, deep slots, hard materials and flexible setups, and higher feeds for rigid setups, coarse-tooth cutters and easy-to-machine materials.
What Designers Can Control
Feed rates are chosen by the machinist or CAM programmer, but the design sets the limits. Aluminum 6061 and brass run faster than stainless steel or titanium. Generous internal radii allow larger, stiffer tools and heavier feeds. Fine surface finishes should only be specified where they matter, because finer finishes require slower finishing passes.
Key takeaways
- Feed rate is the speed at which a cutting tool advances through the workpiece, usually in in/min or mm/min.
- In milling, feed rate = spindle speed × number of teeth × chip load per tooth.
- Spindle speed is how fast the tool rotates in rpm; it is not the same as feed rate.
- Too high a feed rate raises cutting forces and can break the tool; too low a feed rate wastes time.
- Roughing cuts use heavier feeds and lower speeds; finishing cuts use finer feeds and higher speeds.
- Material choice, internal radii and surface-finish requirements set the practical limits for feed rate.
Example
Related terms
References
- Drilling and Milling Speeds and Feeds — University of Florida, EML2322L Design and Manufacturing Laboratory
- Fundamentals of Machine Tools, Chapter 8: Milling Operations — US Army TC 9-524 (hosted by Carnegie Mellon University)