Mechanical Knowledge

The Golden Rule of CNC Milling - Thick in Thin out

What is the The Golden Rule of CNC Milling?

The golden rule of CNC milling is thick in and thin out. Thick in and thin out means that the iron filings are thicker when the tool cuts into the workpiece and thinner when cutting out. With this golden rule of CNC milling, the product finish is good, the lifetime of the tool is longer and it is not easy to vibrate.

As we know, the machining path has a huge impact on tool life. With the increasing automation of the CNC milling programming software, our control of the tool path becomes weaker and weaker, especially the in and out of the cutter, which is almost difficult to be controlled by people. Unfortunately, many software design paths are not in line with our golden rule. Such as program for cut-in path.

How can I get the best tool life during CNC milling programming?

1. Try to use down milling

Regarding down-milling and up-milling, almost all tools are preferred to down-milling, because down-milling conforms to the principle of thick in and thin out. Therefore, except for the following cases, we recommend down milling.

A. The verticality of side milling is not good;

B. The side milling allowance is uneven, or there is black leather;

C. There is clearance in the screw of the machine tool.

Down milling and up milling

2. Use Arc cut and in correct direction

Many people use straight-line cutting when CNC milling programming. We can see from the following 2 cases that thick iron chips are produced when the tool cuts out. The tool is very easy to break.

Wrong cutting method 1: Straight cut

Straight-line cutting

Correct cutting method: Arc cut

Arc cut

Wrong cutting method 2: wrong arc direction

Sandvik has tested, two different cutting methods, the tool life difference is very large, which is more than 4 times.

Therefore, if it is permitted, try to choose arc cutting. If the software can't support it, you can try to cut in obliquely. Oblique cutting can also be thick in and thin out.

At last, we simply analyze the following four kinds of machining paths in CNC milling. 4 machining pathsare arranged in order from bad to the best, The 1st one is bad and the 4th one is the best.

1. Alternating up and down milling, straight-line cutting, and frequently cut-in and cut-out.

2. Down milling, but straight-line cut-in and frequently cut-in and cut-out.

3. Down milling, but straight-line cut-in, no arc corner transition.

4. Down milling, arc cutting, corner arc transition.

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