CNC Knowledge: CNC Machine Tool programming example

Mastering Specialized Arc Programming Instructions in CNC Machining: CT and RND

In the realm of computer numerical control (CNC) machining, programming instructions play a critical role in generating precise and efficient machine movements. Among these instructions, CT and RND are two specialized arc programming instructions that enable machinists to produce complex shapes with ease. In this blog post, we’ll delve into the intricacies of these instructions, their applications, and their advantages in CNC machining.

Understanding CT and RND Instructions

CT (Continuous Tangent) and RND (Radius and Direction) instructions are designed to facilitate the creation of precise arcs and curvatures in CNC machining. These instructions allow for the generation of smooth, continuous arcs, eliminating the need for cumbersome and time-consuming manual calculations.

RND Instruction: Managing Arc Transitions

The RND instruction is responsible for managing the transition of arcs from outline inflection points. It treats the inflection point of the outline with an arc transition from a specified radius and connects it to straight lines or related arcs. This instruction is particularly useful when programming complex shapes with multiple arcs and tangent edges.

Example: Programming with RND Instruction

Let’s consider an example where the RND instruction is used to program an outline with an inflection point. The code snippet below demonstrates how to use the RND instruction to generate a smooth arc transition:

N020 G41 Y-20
N025 G1 Y70 RND = 5
N030 G1 X-40 RND = 5
N035 G3 × 0 CR = 20 RND = 5
N040 G3 × 40 CR = 20 RND = 5
N045 G1 × 70 RND = 5

CT Instruction: Completing Arcs and Tangent Edges

The CT instruction is responsible for completing the connection between straight lines and arcs or tangent edges of circles. This instruction ensures a smooth transition between these elements, eliminating any unwanted deviations or gaps.

Example: Programming with CT Instruction

Here’s an example of how to use the CT instruction to program an arc and tangent edge connection:

N005 G54 G90 G0 Z100 T1 D1
N010 X-90 Y-12
N015 M03 S1000 F500 Z-10
N020 G41 Y-100
N025 G1 Y20
N030 X-60
N040 I
N045 CT X-20 (First Arc R20)
N050 X20 (second arc R20)
N055 X60 (third arc R20)
N060 G1 Y20
N065 G1 × 90
N070 Y-100
N075 m30

Applications of CT and RND Instructions in Polar Coordinate Systems

When working with polar coordinate systems, programming with G2 and G3 instructions can be challenging due to the need to set the pole to the center of the programmed arc. However, the CT and RND instructions efficiently overcome this limitation.

Example: RND Instruction in Polar Coordinate Systems

Here’s an example of using the RND instruction in a polar coordinate system:

N005 G54 G0 T1 D1 Z100
N0110 G111 Ho Yo
N015 AP = 90-15 RP = 110
N020 m03 S1000 F500 Z-10
N025 G42 RP = 100
N030 G1 RP = 0 RND = 10
N035 G1 RP = 100
N040 m30

Example: CT Instruction in Polar Coordinate Systems

This example demonstrates the use of the CT instruction in a polar coordinate system:

N005 G54 G90 GB Z100 T1 D1
N0110 G111 Ho Yo
N015 AP = 90-36-18 RP = 150
N020 m03 S1000 F500 Z-10
N025 G42 RP = 130
N030 G1 RP = 142.66 / 2
N035 CT AP = 90-18
N040 AP = 90 + 18
N045 AP = 90 + 18 + 36
N050 G1 RP = 150
N055 m30

Conclusion

In conclusion, CT and RND instructions are invaluable tools for machinists, enabling them to produce complex shapes with precision and efficiency. By understanding the principles and applications of these instructions, CNC machine operators can streamline their programming process and achieve remarkable results. Whether working in Cartesian or polar coordinate systems, CT and RND instructions prove to be indispensable assets in the world of CNC machining.