What Are Feed and Speed?
In machining, two fundamental parameters control how material is removed: cutting speed (or spindle speed) and feed rate. Cutting speed is the linear velocity of the cutting edge relative to the workpiece, usually expressed in meters per minute (m/min) or feet per minute (ft/min). Feed rate is the distance the tool advances per revolution (in/rev) or per minute (in/min). Getting these values right influences tool life, surface finish, dimensional accuracy and productivity.
Basic Calculations
Both parameters are linked by the tool diameter (D) and the desired material removal rate. The most common formulas are:
- Spindle Speed (N) = (Cutting Speed 1000) ( D)[when speed is in m/min]
- Spindle Speed (N) = (Cutting Speed 12) ( D)[when speed is in ft/min]
- Feed per Revolution (f) = Desired Feed Rate N
- Feed per Minute (F) = f N
For example, to cut aluminum with a 10mm end mill at 200m/min:
Spindle speed N = (2001000) (10) 6366rpm. If the recommended feed is 0.12mm/rev, the feed per minute is 0.126366 764mm/min.
MaterialSpecific Recommendations
Different workpiece materials require distinct speedfeed ranges. The table below gives typical values for common metals when using carbide tools.
| Material | Cutting Speed (m/min) | Feed per Rev (mm/tooth) | Depth of Cut (mm) |
|---|---|---|---|
| Aluminum (alloy) | 150250 | 0.080.20 | 26 |
| Brass | 130200 | 0.070.18 | 25 |
| Mild Steel | 3060 | 0.040.12 | 14 |
| Stainless Steel | 2045 | 0.020.08 | 0.52 |
| Titanium | 1530 | 0.020.06 | 0.51.5 |
These ranges are starting points. Adjustments may be needed based on tool geometry, coolant use, machine rigidity and the specific alloy temper.
Choosing the Right Tool
Tool material, coating, geometry and number of flutes all influence the optimal feedspeed pair.
- Carbide high hardness, allows higher speeds than HSS, especially for aluminum and steel.
- Cobaltbased HSS better heat resistance than plain HSS, suitable for stainless steel at moderate speeds.
- Coatings (TiN, TiAlN, AlTiN) reduce friction and allow higher cutting speeds while extending tool life.
- Flute count fewer flutes (12) evacuate chips better for soft materials; more flutes (34) give finer finishes on hard materials.
- Helix angle larger helix (3045) improves chip flow; smaller helix provides stronger cutting edges for tough alloys.
Best Practices for Optimising Feed and Speed
- Start with manufacturer data. Tool suppliers publish speedfeed charts for each toolmaterial combination.
- Consider machine rigidity. A stiff machine can sustain higher feeds; flexible setups benefit from lower feeds to avoid chatter.
- Use coolant wisely. Flood coolant or mist can increase allowable speeds, especially for steel and titanium.
- Watch tool wear. As the edge dulls, reduce speed or increase feed slightly to maintain chip load and avoid builtup edge.
- Balance productivity and finish. Higher feed rates raise material removal but may sacrifice surface finish. Choose a compromise based on part requirements.
- Document the final settings. Keep a log of spindle speed, feed per rev, depth of cut, tool, and material for future reference.
- Validate with a test cut. Run a short trial on a scrap piece, measure the resulting dimensions and surface, then finetune.
Remember that feed and speed are not static; they should be revisited whenever a variable changes new tool, different batch of material, or a different machine.
