While CNC machining offers high precision and automation, producing a qualified part requires attention to numerous details at each stage, from design and programming to clamping. Slight oversights can lead to scrap, machine collisions, or tool damage.

The following are some key points to focus on during CNC machining, divided into three phases: design, preparation, and execution.

I. Considerations in the Design Phase

This phase determines whether the part can be machined and how easily it can be machined.

1. Handling Internal Sharp Angles (Internal Right Angles)

This is an easily overlooked point. CNC milling cutters are round, so at the corner where two perpendicular surfaces intersect inside the part, the cutter will leave a rounded corner, making it impossible to machine a perfect 90-degree sharp angle.

What to do: If this corner must be rounded, either a process groove (overrun groove) should be provided in the design, or the allowable rounding radius should be specified (usually R≥0.5mm, depending on the tool diameter). 1. If an absolute sharp angle is required, an electrical discharge machining (EDM) step is necessary.

2. Pay attention to minimum wall thickness and cavity depth. Tooling generates vibration during machining.

Thin walls: If the part wall is too thin (e.g., less than 0.5mm for metal, or less than 1mm for plastic), it is easily deformed by the tool during machining, leading to dimensional errors.

Deep cavities: If the machining depth is too deep (e.g., more than 4-5 times the tool diameter), chip removal becomes difficult, the tool is prone to breakage, and the surface finish deteriorates.

3. Pay attention to hole diameter and threads.

Small holes: When machining extremely small holes (e.g., less than 0.5mm in diameter), the drill bit is very prone to breakage, requiring special processes and very high speeds.

Threaded pilot holes: For holes requiring tapping, the design drawing must specify the pilot hole diameter. If the pilot hole is too small, the tap will break inside; if it is too large, the thread will be missing teeth.

II. Precautions during machining preparation

This stage is fundamental to ensuring machining safety and accuracy.

1. **Workpiece Fixing (Clamping) is of Paramount Importance:** The biggest fear in machining is a loosely clamped workpiece that can be displaced by the tool, leading to workpiece failure or even machine damage.

**What to Do:** Ensure the workpiece is firmly pressed onto the machine tool table. For complex parts requiring simultaneous machining of six sides, it's best to design with a clamping allowance (e.g., make it longer and cut it off later), or pre-design the location of the process screw holes to lock the workpiece in place.

2. **Tool Setting and Origin Correction:** Every time a new workpiece or tool is installed, the machine tool must be informed of "where the tool tip is" and "where the workpiece's zero point is."

**What to Do:** Operators must perform tool setting with extreme care. An error in tool setting (e.g., missing a decimal place in the input data) can result in anything from damaged workpiece to broken tools and damaged spindles.

3. **Program Simulation Verification:** Directly sending a pre-written program to the machine tool is very dangerous.


** What needs to be done: Simulation must be performed in computer software first, or the machine tool must be run idle (without cutting material) to observe whether the toolpath is reasonable and whether there is a risk of colliding with the pressure plate or fixture.

III. Precautions during the machining execution phase

1. Focus on chip removal: If chips are not removed in time, they will be cut again by the tool, forming a "chip edge," scratching the workpiece surface, and even clogging the chip removal groove, leading to tool breakage.

What needs to be done: Ensure sufficient pressure and flow of cutting fluid to flush away chips. For deep hole machining, a "pecking drill" method should be used (drill once, retract once, remove chips).

2. Focus on cooling: Cutting generates high temperatures, especially when machining difficult-to-machine materials such as stainless steel and titanium alloys.

What needs to be done: Ensure that cutting fluid is fully poured into the cutting area. If cooling is inadequate, the material will expand due to heat, leading to inaccurate dimensions, or the tool will wear and soften rapidly.

3. Measurement after the first cut: After the program completes the first feature (such as the first hole or the first shape), the machine must be stopped for measurement.

What needs to be done: Confirm that the dimensions are within tolerance before continuing machining. This is a crucial step to prevent batch scrap.

IV. Special Notes for Different Materials

Aluminum Alloy: Soft and prone to tool sticking. Pay attention to chip removal and tool sharpness; otherwise, surface finish will be affected.

Stainless Steel/Titanium Alloy: Severely work-hardened and has poor thermal conductivity. Reduce rotation speed and increase cooling; otherwise, the tool will wear out quickly.

Copper: Soft but with good toughness. Pay attention to burr control, especially edge burrs.

Plastics (e.g., ABS, POM): Low melting point. Ensure adequate cooling; otherwise, the material will melt and stick to the tool. Compressed air is often used for cooling during machining.

In short, CNC machining is more than just pressing a start button. Design should avoid sharp corners and thin walls; during preparation, clamping should be secure and tool setting accurate; during machining, pay attention to chip removal and cooling. Every detail affects the quality of the final product.