Understanding CNC Feeds and Speeds

Every CNC operator wants the magic numbers:

What RPM should I run?
How fast should I feed?
What settings will give me a clean cut without burning, chattering, or breaking a bit?

The honest answer is: it depends.

CNC feeds and speeds depend on your machine, your router bit, your material, your spindle, your toolpath, your workholding, and even how rigid your setup is. That is why feeds and speeds charts and calculators are useful—but they are starting points, not final answers.

The good news is that feeds and speeds become much easier to understand once you focus on one key concept: chip load.

Quick Take

• Feeds and speeds charts are recommended starting points, not universal rules.
• The goal is proper chip load: you want chips, not dust.
• Feed rate is how fast the cutter moves through the material, usually measured in inches per minute (IPM).
• Spindle speed is how fast the tool rotates, measured in revolutions per minute (RPM).
• If your CNC is making dust or burning wood, slowing down may make the problem worse.
• Always make a test cut in scrap material and adjust one variable at a time.

What Are Feeds and Speeds?

In CNC routing, feeds and speeds refers to the relationship between how fast the cutter spins and how fast it moves through the material.

Speed usually means spindle speed or router speed, measured in RPM.

Feed means feed rate, or how fast the tool moves through the material, usually measured in IPM.

These two settings work together. If the spindle spins too fast while the machine moves too slowly, the bit may rub instead of cut. That creates heat, dulls the tool, and can burn wood or melt plastic. If the feed rate is too aggressive for the tool, material, or machine, the bit can chatter, deflect, or break.

The goal is not simply to run faster or slower. The goal is to make the cutter remove the right amount of material with each cutting edge.

The Most Important Concept: Chip Load

Chip load is the amount of material removed by each cutting edge, or flute, during one revolution of the tool.

In practical terms, chip load is the size or thickness of the chip your router bit creates as it cuts.

The basic formula is:

Chip Load = Feed Rate ÷ (RPM × Number of Flutes)

For example, if you increase the feed rate while keeping the same RPM and same bit, each flute takes a larger bite. If you increase RPM while keeping the same feed rate, each flute takes a smaller bite.

That is why the old shop advice is so useful:

You want chips, not dust.

Dust usually means the cutter is not taking a big enough bite. Instead of cutting efficiently, the bit may be rubbing, heating up, and wearing faster than necessary.

Why Chip Load Matters

Getting chip load right affects almost everything about your CNC cut.

• Tool life: Too little chip load can cause rubbing, heat buildup, and premature dulling. Too much chip load can overload the bit and cause breakage.
• Cut quality: A proper chip load helps produce a cleaner edge and a smoother surface finish.
• Heat control: Chips carry heat away from the cut. Dust does not do this nearly as well.
• Productivity: Correct feeds and speeds let you remove material efficiently instead of babying the cut unnecessarily.

When your settings are right, the cut sounds smoother, the chips look more consistent, the bit stays cooler, and the finished edge usually improves.

Feed Rate: How Fast the Tool Moves

Feed rate is how fast the CNC moves the cutter through the material. In the United States, it is usually measured in inches per minute, or IPM.

A higher feed rate means the bit moves through the material faster. This usually creates a larger chip load. A lower feed rate creates a smaller chip load.

But slower is not always safer. If you slow the feed rate too much while keeping RPM high, the bit may start making dust instead of chips. That can increase heat, dull the tool, and cause burning.

Spindle Speed: How Fast the Tool Spins

Spindle speed is how fast the router bit rotates, measured in revolutions per minute, or RPM.

Higher RPM does not automatically mean a better cut. If RPM is too high for the feed rate, each flute removes too little material. That can cause rubbing, heat, burning, or melting.

Lower RPM can help in some situations, especially when cutting plastics or aluminum, but it must still be balanced with feed rate, chip evacuation, and machine capability.

Number of Flutes

The number of flutes on the bit also affects chip load.

A 2-flute bit has two cutting edges. A single-flute bit has one. At the same RPM and feed rate, a single-flute bit takes a larger chip per flute than a 2-flute bit.

That is one reason single-flute and O-flute bits are often used for plastics and aluminum. They create more room for chip evacuation and can help reduce heat buildup in materials that melt or weld easily.

Ramp and Plunge Feed Rates

Your feed rate does not have to be the same for every part of the cut.

When the tool is moving sideways through the material, it can often run at the main cutting feed rate. But when the tool ramps down or plunges into the material, the feed rate usually needs to be slower.

As a general starting point, many CNC users reduce ramp or plunge feed to about half the main feed rate. The right number depends on the bit, material, depth of cut, and toolpath strategy.

Why Feeds and Speeds Charts Are Only Starting Points

Feeds and speeds charts are extremely helpful. They give you a safe, informed place to begin.

But they cannot account for every real-world variable in your shop.

The same router bit cutting the same material may need different settings depending on:

• Machine horsepower
• Machine rigidity
• Spindle or router quality
• Tool diameter
• Number of flutes
• Depth of cut
• Tool stickout
• Workholding
• Material thickness and density
• Dust collection or chip evacuation
• Bit sharpness
• Climb vs. conventional cutting

That is why charts and calculators should be treated as guidelines. They help you avoid wild guesses, but they do not replace test cuts.

Machine Rigidity Changes Everything

One of the biggest reasons feeds and speeds vary is machine rigidity.

A heavy industrial CNC can push a compression bit through MDF at feed rates that would make a desktop CNC chatter, flex, or lose accuracy.

The bit did not change. The material did not change. The machine did.

A rigid machine can hold the cutter more steadily under load. A less rigid machine may flex when the feed rate, depth of cut, or chip load gets too aggressive. That flex can show up as chatter marks, rough edges, poor accuracy, or broken bits.

This is why two CNC users can follow the same chart and get different results. The correct setting is not just about the bit. It is about the entire cutting system.

Example: Why One Operator Runs 260 IPM and Another Runs 720 IPM

In the video above, Jeff refers to the Amana Tool 46172-K 2-flute compression bit. The chart for that series recommends a feed rate of 260 IPM for cutting MDF.

That is a useful starting point.

But Jeff is using a powerful, rigid 7HP machine, so he is able to run at a much higher feed rate—around 720 IPM.

On a smaller desktop CNC, that same bit and material might need a much slower feed rate, such as 120 IPM. The difference is not simply the bit. It is the machine’s horsepower, rigidity, setup, and ability to handle cutting forces.

This is exactly why test cuts matter. A chart can get you close, but your machine tells you the truth.

How Material Affects Feeds and Speeds

Different materials cut differently. A setting that works beautifully in MDF may be completely wrong for acrylic or aluminum.

Common Feeds and Speeds Problems

If Your CNC Is Making Dust

If your cut is producing fine dust instead of chips, your chip load may be too low.

Possible fixes:

• Increase the feed rate.
• Reduce the RPM.
• Use a bit with fewer flutes.
• Check whether the bit is dull.

If Your Router Bit Is Burning Wood

Burning is often a sign of too much heat. One common cause is moving too slowly while the bit spins too fast.

Possible fixes:

• Increase the feed rate.
• Reduce the RPM.
• Use a sharp bit.
• Improve dust collection and chip evacuation.
• Reduce toolpath dwell time in corners or tight areas.

If Plastic Is Melting

Plastic needs to be cut cleanly, not melted. If chips are not clearing the cut, heat can build quickly.

Possible fixes:

• Use an O-flute bit designed for plastics.
• Reduce RPM if necessary.
• Increase feed rate enough to create chips.
• Improve chip evacuation.
• Avoid recutting chips.

If the Machine Is Chattering

Chatter can happen when the cutter, material, or machine setup is not stable enough for the cut.

Possible fixes:

• Reduce feed rate.
• Reduce depth of cut.
• Use a shorter tool stickout.
• Improve workholding.
• Use a more rigid setup.
• Check that the bit and collet are properly installed.

If the Bit Breaks

A broken bit can come from too much cutting force, poor chip evacuation, excessive depth of cut, or a mismatch between the bit and material.

Possible fixes:

• Reduce depth of cut.
• Reduce feed rate if chip load is too high.
• Improve chip evacuation.
• Use the correct bit for the material.
• Check tool stickout and workholding.
• Make sure the collet is clean and properly tightened.

How to Dial In Feeds and Speeds

The best way to find the right feeds and speeds is to start with a reliable recommendation, then adjust based on the cut.

1. Start with the manufacturer’s chart or calculator. This gives you a reasonable starting point for the bit and material.
2. Make a test cut in scrap material. Use the same material, thickness, and workholding method whenever possible.
3. Look at the chips. You want actual chips, not dust, burning, melting, or powder.
4. Listen to the cut. A smooth, steady cutting sound is usually better than screeching, squealing, or heavy vibration.
5. Inspect the edge. Look for burning, fuzzing, chatter marks, melting, tearout, or poor finish.
6. Adjust one variable at a time. Change feed rate, RPM, depth of cut, or tooling—but do not change everything at once.
7. Record what works. Keep notes for each bit, material, and machine setup.

Do Higher RPMs Require Higher Feed Rates?

Not always, but often they are connected.

If you increase RPM while keeping the same feed rate, your chip load gets smaller. In some cases, that may cause rubbing, dust, heat, or burning. To maintain the same chip load, you would need to increase the feed rate as RPM increases.

But this is not a rule you can apply blindly. Your machine still has limits. Your bit still has limits. Your material still has limits.

That is why the answer to most feeds and speeds questions is not simply “faster” or “slower.” The answer is to maintain the right chip load for your tool, material, and machine.

There Are No Universal Rules

Feeds and speeds are part science, part experience.

Charts and formulas can help you predict a good starting point. But they cannot know the exact condition of your machine, the sharpness of your bit, the rigidity of your setup, or the behavior of your specific material.

That is why experienced CNC operators test, listen, inspect, and adjust.

The goal is not to copy someone else’s settings perfectly. The goal is to find the combination that produces clean chips, a smooth finish, and minimal tool wear on your machine.

Final Thoughts

Feeds and speeds charts are not wrong. They are simply starting points.

Start with the recommended settings. Make a test cut. Watch the chips. Listen to the machine. Inspect the edge. Then adjust one variable at a time.

Once you understand chip load, feeds and speeds become much less mysterious. You will spend less time guessing, less time burning material, and more time cutting confidently.