1. General Precautions for Machining
(1) When the workpiece is too high, roughing should be performed in layers using tools of different lengths. After roughing with a large-diameter cutter, the remaining stock should be cleared with a smaller cutter.
(2) Use flat-end mills for machining flat surfaces; ball-end mills should be used sparingly to reduce machining time. If the surface has a slope and the angle is an integer, use an angle cutter.
(3) Set tolerances reasonably to balance machining accuracy and computer calculation time. Use more operations to reduce idle tool travel time.
(4) For workpiece materials with high hardness, choose conventional (up) milling; for low hardness, choose climb (down) milling. Use conventional milling for roughing and climb milling for finishing.
(5) Tool materials with good toughness but lower hardness are suitable for roughing; those with lower toughness but higher hardness are suitable for finishing.

2. CNC Machining Process
(1) Workpiece Clamping Method and Fixture Selection
On CNC machine tools, the clamping method for the workpiece should also reasonably select the positioning datum and clamping scheme. When selecting the fine datum, the principles of “datum uniformity” and “datum coincidence” should generally be followed. In addition to these two principles, the following should also be considered:
a. Try to complete the machining of all surfaces in one positioning and clamping operation. Therefore, choose a positioning method that facilitates the machining of all surfaces.
b. When the workpiece is clamped in one setup, it should be possible to machine all its surfaces.
c. When determining the placement position of the workpiece on the worktable, take into account the machining of all stations, as well as the influence of tool length and tool rigidity on machining quality.
d. For fixtures used in CNC machining, prefer those assembled from standard components and adjustable, so as to shorten the production preparation cycle.

(2) Arrangement of Machining Sequences
When arranging the machining sequence, basic principles must be followed, including “faces before holes” and “roughing before finishing.” In addition to these, the following guidelines should also be observed:
a. Arrange operations by tool concentration to avoid repeated use of the same tool multiple times, thereby reducing tool change frequency and time.
b. For hole systems with high coaxiality requirements, complete all machining of that hole system after one positioning, before machining hole systems at other coordinate positions. This eliminates errors caused by repeated positioning and improves the coaxiality of the hole system.
c. Determine and select the tool starting point and tool change point. Once determined, they should not be changed arbitrarily.