Feed Rate and Plunge Rate Calculator
Calculate CNC feed rate, plunge rate, surface speed, material removal rate, and cut time from RPM, flute count, chipload, tool diameter, material, and engagement.
Feed and Plunge Results
| Material | Typical Surface Speed | Starter Chipload | Common Plunge Factor |
|---|---|---|---|
| Softwood | 600-1000 SFM | 0.004-0.010 in/tooth | 35-55% of feed |
| Hardwood | 350-650 SFM | 0.003-0.007 in/tooth | 25-45% of feed |
| Plywood | 450-750 SFM | 0.004-0.009 in/tooth | 30-45% of feed |
| MDF | 500-850 SFM | 0.005-0.012 in/tooth | 35-50% of feed |
| Acrylic | 250-500 SFM | 0.002-0.006 in/tooth | 20-35% of feed |
| Aluminum | 300-800 SFM | 0.0015-0.006 in/tooth | 12-30% of feed |
| Mild steel | 80-250 SFM | 0.0008-0.003 in/tooth | 8-20% of feed |
| Stainless steel | 50-160 SFM | 0.0005-0.002 in/tooth | 6-16% of feed |
| Tool Type | Diameter | Flutes | Best Starting Use |
|---|---|---|---|
| Single O-flute | 1/8-1/4 in | 1 | Plastic, foam, aluminum chip evacuation |
| Compression spiral | 1/4-3/8 in | 2 | Plywood sheets and veneered panels |
| Upcut carbide end mill | 3-10 mm | 2-3 | Aluminum pockets and profiles |
| General carbide end mill | 6-12 mm | 3-4 | Steel profiles with coolant and rigid holding |
| Surfacing cutter | 1-2 in | 2-4 | Spoilboard and wide shallow passes |
| V-bit engraving cutter | 0.1-0.5 mm tip | 1 | Engraving with light chipload settings |
| Output | Formula | Imperial Units | Metric Units |
|---|---|---|---|
| Feed rate | RPM x flutes x chipload | in/min | mm/min |
| Plunge rate | Feed x plunge factor | in/min | mm/min |
| Cutting speed | pi x diameter x RPM | SFM using in / 12 | m/min using mm / 1000 |
| MRR | Feed x width x depth | in³/min | cm³/min from mm³ |
| Cut time | Length x passes / feed + approach | minutes and seconds | minutes and seconds |
| Setup | Typical Tool | Feed Start | Plunge Start |
|---|---|---|---|
| Hardwood profile | 1/4 in 2-flute spiral | 90-160 in/min | 25-55 in/min |
| Plywood sheet cut | 1/4 in compression | 140-230 in/min | 45-85 in/min |
| Acrylic slot | 1/8 in O-flute | 45-95 in/min | 10-28 in/min |
| Aluminum adaptive | 6 mm 3-flute carbide | 600-1800 mm/min | 120-420 mm/min |
| Steel light profile | 8 mm 4-flute carbide | 120-450 mm/min | 20-80 mm/min |
| Spoilboard surfacing | 1-1/2 in surfacer | 160-260 in/min | 30-70 in/min |
After pressing the cycle start button you hear the CNC spindle scream like a turbine and you know you guessed at the feed rate rather than calculated it. Panic ensues as you notice smoke rising off the board because you didn’t match the math to the machine.
The machine doesn’t care what you intend but will only respond to the math. Getting the numbers right make the difference between a clean surface and a ruined part. It saves a burned motor and a dull bit.
Why You Need To Do The Math For CNC Cutting
A common mistake many newbies make is mistaking speed for feed. They’ll bump up their RPM in hopes that faster is better, meanwhile they keep their feed rate low. This results in a spinning spindle and a slow-moving bit through the material. The cutting edge begin rubbing against the material different than slicing through the wood. Friction produces heat which softens the wood and gunk’s up the flutes. You need to match linear travel with rotational speed.
Once you enter your spindle speed and tool diameter into the calculator on the page, it figure out the math for you. You no longer need to convert surface feet per minute to inches per minute yourself. The solution is all about chip load.
What is chip load? Chip load is the thickness of a material being shaved off by each flute for each revolution of the tool. Too little chip load and the tool will polish the material rather than cut it away. Too great of a chip load and either motor stalls or the bit breaks. To determine the proper chip load you input what size chip load you would like and then the tool on the page calculates the actualy feed rate to enter into your machine. It takes out the guesswork in the process.
Plunging is even worse. That’s when the bit plunges vertically into the material. No side-to-side movement exist which would sweep chips off the cutting edge. It just piles them right up against the tip where there is tremendous heat and pressure being generated. Almost everywhere, plunging is measured as a percentage of your lateral feed speed. I’d suggest starting at about 30-40% of your regular feed with wood. Metals would be slower then.
The chart on the page explain it all by material type. Don’t plunge aluminum like you do MDF. Chip removal physics will be entirely different.
Another output is material removal rate, which gives you a view of the machine’s workload. By multiplying width of cut, depth of cut, and feed rate we get an idea of how much volume the machine is removing per minute. If the machine isn’t powerful enough to handle this amount of work, the spindle will bog down. The pitch will drop and you’ll notice poor cut quality. Better to make several shallow passes instead of one aggressive deep cut. Not only does this extend life of your tooling but it keeps the load manageable.
The real-world advantage of this is that it gets you cutting. You can estimate how much time you have available on the machine so you can plan out your workday. You can determine whether it’s worth leaving the machine running overnight, or if you should of just wait until someone frees it up. The calculator adds up total cutting length and divides it by your feed rate. It accounts for ramping time as well as approach moves, giving you a realistic estimate. Then you know how long it’ll be before you can unload your part.
CNC machines is all about precision. Precision isn’t a feeling or an intuitive sense. It’s following the numbers. You need to believe the math more than what feels right. If you do the math on the plunging rate and feed rate, it is time to hit the start button. You can be confident the machine will hum with a clean cutting action as the chips fly. And that’s doing the math prior to touching the power button.
