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When designing a CNC-machined part, you may not initially consider which type of machine will be used. However, the machine type directly impacts the complexity of the geometry you can achieve.
The key distinction between 3-axis, 4-axis, and 5-axis machining lies in the movement capabilities of both the workpiece and the cutting tool. As the number of axes increases, the machining process allows for greater flexibility and more intricate geometries. A higher-axis machine enables more precise cuts, reduces the need for repositioning, and allows for the creation of more complex parts in a single setup.
The most simple type of machining, where the workpiece is fixed in a single position. Movement of the spindle is available in the X, Y and Z linear directions.
3-axis machines are typically used for machining of 2D and 2.5D geometry. In 3-axis machining, all six sides of a part can be machined, but each side requires a separate fixturing setup, which can add to production costs. With a single fixture setup, only one side of the part can be machined at a time, making it less efficient for complex geometries that require multiple repositionings.
3-axis CNC milling is highly capable of producing complex and practical shapes, particularly when handled by an advanced machining facility. It is ideal for creating planar milled profiles, drilling, and threading holes aligned with an axis. Additionally, undercut features can be achieved using specialized tools such as T-slot and dovetail milling cutters.
However, certain features may be unachievable with a 3-axis machine or may be more cost-effective to produce using a 4- or 5-axis machine. Specifically, 3-axis milling cannot accommodate features positioned at an angle to the X-Y-Z coordinate system, even if the feature itself is planar. When designing CNC-machined parts, it’s important to distinguish between different types of angled features to determine the most efficient machining approach.
An angled feature is machined at an angle relative to one of the primary X, Y, or Z axes. For example, a planar milled surface positioned at 45° to the X-axis requires a rotation of the A-axis.
A compound angle feature is machined at an angle relative to two axes simultaneously. For instance, a planar surface angled at 45° to the X-axis and 30° to the Z-axis requires complex multi-axis movements.
Both angled and compound angle features cannot be machined using a 3-axis CNC machine and require either a 4-axis or 5-axis CNC s4-Axis Machining
4-axis machining introduces an additional rotational movement about the X-axis, known as the A-axis. Like in 3-axis machining, the spindle moves along three linear axes (X, Y, and Z), but with the A-axis, the workpiece can rotate. Most 4-axis machines follow a vertical machining setup, where the spindle rotates around the Z-axis, while the workpiece is mounted along the X-axis and rotates with the fixture in the A-axis. This setup allows machining on four sides of a part in a single fixture setup.
4-axis machining can be a more cost-effective alternative for parts that could theoretically be machined using a 3-axis machine but would require multiple fixtures. For example, a recent part we machined using a 4-axis setup eliminated the need for two separate fixtures, reducing costs from £1,800 (for two 3-axis fixtures) to £1,000 (for a single 4-axis fixture). Additionally, avoiding fixture changeovers reduced human error, improved precision, and minimized the need for extensive quality control measures. Maintaining a single fixture also allows for tighter tolerances between features on different sides of the part.
There are two primary types of 4-axis machining:
- Indexed (or Positional) 4-Axis Machining: The A-axis rotates while the machine is idle. Once the workpiece is correctly positioned, the axis is locked in place, and cutting resumes.
- Continuous 4-Axis Machining: The machine performs cutting operations while the A-axis rotates simultaneously. This enables the machining of complex arcs, such as cam profiles and helical features.
4-axis machining enables the production of angled features that are not possible with a 3-axis machine. However, all angled features must be aligned with the same rotational axis in a single setup. If multiple angled orientations are required, additional fixture setups or a 5-axis machine may be necessary.etup for accurate manufacturing.
5-axis CNC milling machines utilize two of the three possible rotational axes, depending on the machine type. These machines either rotate along the A-axis and C-axis or the B-axis and C-axis. The rotation can occur either through the movement of the workpiece or by adjusting the spindle.
There are two main types of 5-axis CNC machines: 3+2 axis machines and fully continuous 5-axis machines.
In 3+2 axis machining, the two rotational axes operate independently, allowing the workpiece to be positioned at any compound angle relative to the cutting tool before machining begins. However, simultaneous movement of both rotational axes during machining is not possible. Despite this limitation, 3+2 machining can produce highly intricate 3D shapes.
In contrast, fully continuous 5-axis machining enables simultaneous movement of the two rotational axes while the cutting tool moves linearly along the XYZ coordinates. This capability allows for the creation of not only planar compound-angled features but also highly complex curved 3D surfaces. As a result, fully continuous 5-axis machining can manufacture intricate parts that would typically require molding processes.
