CNC Chip Load Calculator
Use this tool to calculate chip load per tooth and to estimate a safe starting feed rate from your desired chip load.
Reverse Calculator (Find Feed Rate)
Formula: Chip Load = Feed Rate ÷ (RPM × Number of Flutes)
What is chip load?
Chip load is the thickness of material removed by each cutting edge (tooth) every time it engages the workpiece. In practical terms, it tells you how hard each flute is working. If chip load is too low, tools tend to rub and heat up instead of cutting efficiently. If chip load is too high, cutting forces spike and you can see chatter, poor finish, or broken tools.
Chip load formula
The most common relationship in CNC routing and milling is straightforward:
You can rearrange it to solve for feed rate when you already have a target chip load:
These formulas are exactly what the calculator above uses.
How to use this calculator
1) To find chip load from your current settings
- Enter spindle speed (RPM).
- Enter number of flutes on your tool.
- Enter your programmed feed rate and choose unit (IPM or mm/min).
- Click Calculate Chip Load.
2) To estimate feed rate from a target chip load
- Enter RPM and flute count.
- Enter desired chip load (in/tooth or mm/tooth).
- Click Calculate Feed Rate.
Good chip load depends on more than one number
Chip load is central, but it does not work alone. Real-world results depend on material, cutter geometry, stickout, machine rigidity, workholding, radial engagement (stepover), and axial depth of cut. Use the output here as a strong starting point, then tune from test cuts.
Typical starting chip load ranges (general guidance)
| Material | Small Tools (1/8"–1/4") | Larger Tools (3/8"–1/2"+) |
|---|---|---|
| Hardwood / Plywood | 0.002" – 0.006" | 0.004" – 0.012" |
| MDF / Softwood | 0.003" – 0.008" | 0.006" – 0.015" |
| Plastics (acrylic, HDPE) | 0.002" – 0.006" | 0.004" – 0.010" |
| Aluminum (router-class setup) | 0.0008" – 0.003" | 0.0015" – 0.005" |
Note: These ranges are approximate and intended for initial setup only. Always verify with your tool manufacturer data first.
Common mistakes when setting feeds and speeds
- Ignoring flute count: More flutes with the same feed means lower chip load.
- Running high RPM + low feed: This often causes rubbing, heat, and early tool wear.
- Copying settings blindly: Tool geometry and machine stiffness can change everything.
- Confusing units: IPM vs mm/min and in/tooth vs mm/tooth mistakes are common.
- No test pass: A short trial cut saves tools, stock, and time.
Practical tuning workflow
- Start with vendor-recommended chip load for your cutter and material.
- Use the reverse calculator to get feed rate at your chosen RPM and flute count.
- Run a short test cut and inspect chips, heat, sound, and finish.
- Adjust one variable at a time (feed, RPM, depth, stepover).
- Log the final recipe for repeatability.
FAQ
Should I always increase feed if my tool is burning wood?
Often yes, but not always. Burning can come from low chip load, dull tooling, poor chip evacuation, or too much radial engagement. Check all of them before making large feed jumps.
Is higher chip load always better?
No. Very high chip load can overload the cutter and machine. The goal is balanced cutting: thick enough chips to carry heat away, but not so thick that deflection or breakage occurs.
Why does my finish get worse even when chip load is in range?
Surface finish can degrade from chatter, runout, weak fixturing, spindle issues, or incorrect toolpath strategy. Chip load is necessary, but not sufficient by itself.