Speeds & Feeds Calculator
Calculate optimal spindle speed (RPM) and feed rate for CNC milling. Supports metals, plastics, and wood.
Speeds & Feeds Calculator
Calculate optimal RPM and feed rate for CNC milling
Tool Parameters
Spindle Speed
4,889 RPM
revolutions per minute
Feed Rate
70.4 IPM
inches per minute
0.0048" per tooth
thickness per flute
640 SFM
surface feet/min
3.52 in³/min
volume rate
0.85 sec
cutting time
G-Code Reference
Formulas Used
Understanding Speeds & Feeds
Proper speeds and feeds are critical for tool life, surface finish, and productivity. Running too slow wastes time; running too fast damages tools and workpieces.
Key Parameters
- SFM: Surface speed determined by material and tool type
- RPM: Spindle revolutions - depends on SFM and tool diameter
- Feed Rate: Table movement speed (IPM or mm/min)
- Chip Load: Material thickness per tooth per revolution
Material Guidelines
Metals
- Aluminum: 600-1000 SFM, aggressive chip loads
- Mild Steel: 80-120 SFM, moderate chip loads
- Stainless: 40-80 SFM, maintain cutting pressure
- Titanium: 30-60 SFM, rigid setup required
Non-Metals
- Plastics: 500-800 SFM, sharp tools, high feeds
- Hardwood: 600-1000 SFM, chip evacuation critical
- Softwood: 800-1200 SFM, prevent burning
- Composites: 300-600 SFM, dust collection essential
Frequently Asked Questions
What is Surface Feet per Minute (SFM)?
SFM is the speed at which the cutting edge of the tool moves across the workpiece surface. It's determined by the material being cut and the tool type. Aluminum can handle 800+ SFM, while stainless steel may need only 50-100 SFM.
How do I calculate RPM from SFM?
RPM = (SFM × 12) / (π × Tool Diameter). For example, cutting aluminum at 800 SFM with a 0.5" endmill: RPM = (800 × 12) / (3.14159 × 0.5) = 6,112 RPM.
What is chip load and why does it matter?
Chip load is the thickness of material each flute removes per revolution. Too low causes rubbing and heat; too high risks tool breakage. Typical chip loads range from 0.001" (hardened steel) to 0.010" (softwood).
Should I use climb milling or conventional?
Climb milling (cutter moves with feed direction) generally provides better surface finish and longer tool life. Conventional milling may be better for older machines with backlash or when roughing tough materials.
How do I know if my feeds and speeds are wrong?
Signs of incorrect parameters: excessive chatter/vibration, poor surface finish, discolored chips (too much heat), broken tools, or excessive tool wear. Blue chips indicate overheating - reduce speed or increase feed.
What's the difference between roughing and finishing?
Roughing uses higher chip loads and deeper cuts to remove material quickly. Finishing uses lower chip loads and shallower cuts for better surface finish. Our calculator adjusts SFM and chip load accordingly.
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