CNC Feed Rate Calculator
Selects recommended surface speed and chip load presets.
SFM (ft/min) for Imperial or m/min for Metric. Pre-filled from material selection.
Material removed per tooth per revolution. Pre-filled from material selection.
Enter Your Tool & Material Details
Select a material, enter your tool diameter and flutes, then choose your spindle RPM or surface speed to calculate feed rate, plunge rate, stepover, pass depth, and material removal rate.
How to Use the CNC Feed Rate Calculator
Select Material and Operation
Choose your workpiece material from the dropdown — this pre-fills recommended surface speed and chip load values. Select the operation type (Milling, Drilling, Boring, or Reaming) to apply the correct process modifier to the feed rate.
Enter Tool Geometry
Input your tool diameter (in inches or mm depending on unit selection), select the number of flutes, and choose the tool type. Then select the coating and coolant type — these apply industry-standard multipliers to the surface speed to give you the best permissible cutting velocity for your setup.
Set RPM or Surface Speed
Switch between 'From Surface Speed' mode (RPM is calculated from SFM/m/min) or 'From Direct RPM' mode (feed rate is calculated directly from your machine's spindle speed). The surface speed and chip load fields are pre-filled but editable — adjust them to match your tool manufacturer's recommendations or known good values.
Review Results and Check Safety
Read the primary results (Feed Rate, RPM, Plunge Rate) and check the Parameter Safety bar. A green indicator means your parameters are within safe operating ranges. Yellow means caution — verify pass depth and stepover. Red means the settings are aggressive and risk tool breakage. Use the Roughing vs Finishing comparison to plan your complete machining strategy, and export or print the results for your machine operator.
Frequently Asked Questions
What is the basic formula for CNC feed rate?
The fundamental feed rate formula is: Feed Rate = RPM × Number of Flutes × Chip Load per tooth. First, calculate spindle RPM from surface speed: RPM = (SFM × 3.82) / Tool Diameter for Imperial units, or RPM = (Vc × 1000) / (π × D) for Metric. Chip load is the material removed per tooth per revolution — it is the primary variable that controls cutting forces and heat generation. The correct chip load depends on material hardness, tool diameter, and operation type, and is typically found in the tool manufacturer's cutting data sheets or reference databases like those used by this calculator.
What is chip load and why does it matter?
Chip load (also called feed per tooth or IPT — inches per tooth) is the thickness of the chip produced by each cutting edge per revolution. It is the most critical feeds and speeds parameter. Too low a chip load causes rubbing rather than cutting — the edge slides along the material surface without actually shearing a chip, generating friction heat that dulls the tool rapidly and can work-harden materials like stainless steel. Too high a chip load produces excessive cutting forces that can break end mills, cause chatter (poor surface finish), and deflect the tool away from the programmed path. The correct chip load is determined by tool diameter, material, and flute count.
What is surface speed (SFM) and how do I choose the right value?
Surface Feet per Minute (SFM) — or Meters per Minute (m/min) in metric — is the velocity of the cutting edge relative to the workpiece surface. It determines the heat generated at the cut: higher SFM means more heat. Each material has a recommended SFM range based on its hardness, thermal conductivity, and chemical reactivity with tool materials. Soft materials like wood can handle 800–1000 SFM with carbide. Aluminum runs at 300–500 SFM dry or 500–700 SFM with coolant. Stainless steel is limited to 100–250 SFM due to work-hardening risk. Titanium requires 80–150 SFM to prevent thermal damage. This calculator pre-fills material-appropriate SFM values.
What is chip thinning and when should I enable it?
Chip thinning occurs when your radial engagement (stepover) is less than 50% of the tool diameter. In this geometry, the arc of engagement is reduced, which means the actual chip thickness produced is less than the programmed chip load. The result is that you are not generating proper chips — you are rubbing more than cutting. The correction is to increase the programmed feed rate using the formula: Adjusted Chip Load = Desired Chip Load × sqrt(Diameter / (2 × Radial Width)). Enabling chip thinning in this calculator automatically computes the corrected feed rate, allowing you to achieve proper chip formation in low-radial-engagement or high-efficiency milling (HEM) toolpaths.
How do tool coatings affect speeds and feeds?
Tool coatings improve hardness, lubricity, and thermal resistance, allowing higher cutting speeds without premature wear. TiN (titanium nitride) is the classic golden coating adding ~10% speed capacity. TiAlN (titanium aluminum nitride) is more heat-resistant and adds ~25%, making it excellent for steels and high-temperature alloys. AlTiN (aluminum titanium nitride) adds ~40% and performs best at high temperatures common in hard steels. Diamond coatings add ~50% and are essential for abrasive materials like carbon fiber, fiberglass, and graphite. Uncoated carbide is the baseline — still excellent for many materials including aluminum where diamond or TiAlN coatings can cause built-up edge.
What is material removal rate (MRR) and how do I use it?
Material Removal Rate (MRR) measures cutting efficiency as a volume of material removed per unit time — in³/min or mm³/min. It is calculated as: MRR = Feed Rate × Axial Depth of Cut × Radial Stepover. A higher MRR means faster machining and lower cost per part, but requires more spindle power and puts more stress on the tool and machine. MRR is useful for comparing roughing strategies (large depth, wide stepover, lower feed) versus trochoidal or high-efficiency milling toolpaths (shallow depth, small stepover, very high feed with chip thinning correction). When machine power is limited, MRR helps you find the optimal balance between depth of cut and feed rate.