CNC machining relies on three core elements to deliver efficient, high-quality results: cutting speed, tool feed, and depth of cut. These elements are like the “engine, transmission, and fuel” of a car. Each works independently, yet they must stay in perfect balance. If you get the settings wrong, you risk tool damage, poor surface finishes, or wasted production time.
This guide breaks down each element of CNC machining. We will help you solve common parameter-setting problems and optimize your workflow for precision and speed.
What Is the “Speed Limit” for Your Tools?
Cutting speed is the speed at which the tool and the workpiece move relative to each other. We measure it in meters per minute (m/min). It is the primary factor that determines how long your tool will last.
Factors That Define Cutting Speed
Cutting speed is not a one-size-fits-all number. It depends on three critical factors:
- Tool Material: Harder tools handle higher heat. Carbide tools can run 3 to 5 times faster than High-Speed Steel (HSS) tools.
- Workpiece Material: Soft metals like aluminum allow for much faster speeds than hard metals like stainless steel.
- Coolant Use: Wet machining with coolant lets you increase speed by 20% to 30% because it reduces friction and heat.
| Tool Material | Workpiece Material | Dry Speed (m/min) | Wet Speed (m/min) |
| Carbide | Aluminum | 300–500 | 400–600 |
| Carbide | Stainless Steel | 80–120 | 100–150 |
| HSS | Aluminum | 100–150 | 120–180 |
| HSS | Stainless Steel | 20–40 | 30–50 |
Common Problem Solved: “Why is my tool wearing out too fast?” You are likely running too hot. If you run a carbide tool on stainless steel at 200 m/min dry, it might fail in 30 minutes. Drop the speed to 100 m/min, and the tool could last for 6 hours.
How Does Tool Feed Affect Your Surface?
Tool feed is the distance the tool moves along the workpiece per revolution. It balances two things: surface quality and efficiency.
Choosing the Right Feed Rate
The right feed depends on your machining stage:
- Rough Machining: Use a larger feed rate (0.2–0.5 mm/rev) to remove material fast. A 0.4 mm/rev feed can cut a block twice as fast as a 0.2 mm/rev feed.
- Finish Machining: Use a smaller feed rate (0.05–0.15 mm/rev) for a smooth look. This creates a surface roughness (Ra) of 1.6 $\mu$m, which is ideal for consumer electronics.
Why Rigidity Matters
You must consider the power of your machine and the stiffness of your tool. A weak machine cannot handle heavy feeds without stalling. Likewise, long and thin tools need smaller feeds to avoid vibration, which ruins the surface finish. Short, thick tools can handle much more aggressive feeds.
Can You Cut Deeper Without Breaking Tools?
Depth of cut is the distance the tool penetrates the workpiece in a single pass. It is all about cutting down the number of passes to save time.
Rules for Setting Depth
- Rough Cuts: Use the largest depth your machine can handle. For a carbide tool in aluminum, a 5–10 mm depth is often safe. This finishes the job in fewer passes.
- Hard Materials: For titanium or stainless steel, keep the depth under 2–3 mm per pass to reduce tool stress.
- Finishing Passes: Use a tiny depth of 0.1–0.5 mm. This cleans up imperfections without changing the part’s final size.
Common Problem Solved: “Why is my part bending?” This often happens with thin materials. A 2 mm thick aluminum sheet cannot handle a 1.5 mm depth of cut. If you reduce the depth to 0.5 mm, the sheet stays flat and accurate.
How to Balance the Three Elements?
The real skill lies in balancing all three. Follow this step-by-step process:
- Select Cutting Speed: Start here based on your tool and material. (e.g., Carbide + Aluminum = 400 m/min).
- Determine Tool Feed: Match this to your goal. Roughing = 0.3 mm/rev; Finishing = 0.1 mm/rev.
- Set Depth of Cut: Go as deep as is safe for the material and machine.
- Test and Adjust: Run a sample. If the tool wears too fast, lower the speed. If the surface is rough, lower the feed.
Real-World Machining Scenarios
| Project | Tool/Material | Speed (m/min) | Feed (mm/rev) | Depth (mm) |
| Phone Case | Carbide/Aluminum | 400 (Wet) | 0.3 $\rightarrow$ 0.1 | 5.0 $\rightarrow$ 0.3 |
| Steel Gear | Carbide/Stainless | 120 (Wet) | 0.2 $\rightarrow$ 0.08 | 2.0 $\rightarrow$ 0.2 |
| Drill Bit | HSS/Carbon Steel | 30 (Dry) | 0.15 | 10.0 (Single) |
FAQ
Can I use the same cutting speed for milling and drilling?
No. Drilling usually requires slower speeds. Drills have smaller cutting edges that struggle to clear heat. For example, a carbide drill on aluminum should run at 250 m/min, while a mill can handle 400 m/min.
What happens if I set the tool feed too low?
A very low feed rate wastes time and causes “rubbing.” Instead of cutting, the tool slides over the metal. This creates friction that wears the tool out much faster than a proper cut would.
Do different tool types need different depths of cut?
Yes. End mills are designed for side-loading and can handle large depths. Drills are less rigid. A 10 mm drill should only take 2–3 mm per pass, whereas a 10 mm end mill can often handle 8 mm in aluminum.
Discuss Your Projects with Yigu Rapid Prototyping
Need help finding the perfect settings for your next project? At Yigu Rapid Prototyping, we provide expert guidance on material selection and parameter optimization. Whether you are working with tough stainless steel or high-speed aluminum, our team ensures your parts are made with precision and efficiency. Would you like me to generate a specific parameter sheet for your current project?