By Sophia Wong | 24 June 2025 | 0 Comments
What is RTCP in CNC ? （Detailed more than 2000 words)
What is RTCP in CNC ?
CNC 5 axes (including 5 axis CNC Router, 5 axis cnc machining center etc) achieve complex surface processing through three linear axes (X/Y/Z) and two rotary axes (two of A/B/C). In traditional 3 axis processing, the tool center point (TCP) path is consistent with the programmed path; but when the 5 axis are linked, the movement of the rotary axis will change the spatial orientation of the tool relative to the workpiece, resulting in:
RTCP (Rotational Tool Center Point Control) is the core technology created to solve this problem. Its core idea:
"No matter how the rotary axis moves, the control system always dynamically compensates the tool center point position so that it strictly follows the programmed path."
1. Technical principles and mathematical foundations of RTCP in CNC
1). Core algorithm: coordinate transformation and kinematic inverse solution
The essence of RTCP is to map the tool path from the workpiece coordinate system (programming coordinate system) to the machine tool motion coordinate system through real-time coordinate transformation
2). Dynamic compensation process:
Read the TCP coordinates and tool direction of the current programming point
Calculate the actual tool tip position offset according to the rotation axis angle
Adjust the linear axis position compensation offset in real time
Ensure that the tool tip is always at the programming position
3). Mathematical example (simplified model):
Assume that the rotary table (B axis) rotates at an angle of θ and the tool arm length is L:
Without RTCP: Tool tip offset = L × (1 - cosθ)
After enabling RTCP: Z axis automatically moves down to compensate ΔZ = L × (1 - cosθ)
Figure 1: RTCP compensation algorithm flow chart
2). Implementation of the core functions of RTCP in the 5 axis CNC machine
1. Dynamic locking of the tool center point
Function: No matter how the A/B/C axis rotates, the tool tip coordinates (X, Y, Z) strictly follow the G code path
Realization: The CNC system solves the Cartesian coordinate offset caused by the rotation in real time and offsets it through the linear axis linkage
2. Tool direction vector control
Function: Keep the tool axis consistent with the surface normal (key for engraving steep side walls)
Realization: Dynamically adjust the rotation axis angle according to the surface model data
3. Elimination of non-linear errors
Problem: The non-orthogonal structure of the rotation axis (such as swing head + turntable) causes motion coupling errors
RTCP solution: Preset machine tool geometric parameters (such as axis offset, pivot distance) in the kinematic model
4. Simplified program writing
Traditional method: The rotation axis position needs to be pre-calculated in the CAM software → The program is lengthy and error-prone
RTCP mode: Directly output the tool path (XYZ + tool axis vector) → G code volume is reduced by 50%+
3). Typical application of RTCP in 5 axis cnc wood router
1. Complex wooden surface engraving
2. Deep cavity/narrow gap processing on wood
Problem: Tool elongation causes rigidity to decrease, and the side wall is prone to vibration
RTCP solution: By adjusting the tool inclination angle, side milling is converted to end milling (improving rigidity)
3.Multi-angle feature processing
4). RTCP system implementation architecture
1. Hardware requirements
2. Software workflow
• Input: 3D model of workpiece
• CAM stage: Generate CL file containing tool position (XYZ) and tool axis vector (I, J, K)
• Post-processing: Convert to G code (such as G43.4 to open RTCP mode)
• CNC system:
lAnalyze tool axis vector
lReal-time kinematics inversion
lGenerate servo instructions for each axis
3. Key CNC instructions gcode
G54 ; Workpiece coordinate system
G43.4 H01 ; Enable RTCP (Tool Length Compensation Mode)
G01 X100 Y50 Z-10 I0 J0 K1 F500 ; Linear interpolation (K=1 means vertical downward)
Picture 3：RTCP control system architecture
+-------------------+ +-------------------+ +-------------------+
| CAMsoftware | | cnc system | | servo system |
| (create XYZ+IJK) |---->| RTCP mode |---->| (Run compensatory movements) |
| | | ┌─────────────┐ | | |
| | | │ Kinematics Solver │ | | X axis：±0.005mm |
| | | │ Real-time calculationΔXYZ │ | Y axis：±0.005mm |
+-------------------+ | └─────────────┘ | | Z axis：±0.003mm |
| ┌─────────────┐ | | A axis：±0.001° |
| │ Tool radius compensation│ | B axis：±0.001° |
| └─────────────┘ | +-------------------+
+-------------------+
▲
│
+-------------------+
| Linear scale feedback |
| (Closed-loop position detection) |
+-------------------+
5). Technical advantages and economic benefits brought by RTCP
1. Accuracy improvement comparison
2. Efficiency optimization data
Programming time reduction: reduce manual calculation of rotary axis position → save 30% CAM time
Processing cycle compression: avoid repositioning → complex workpiece processing speed increased by 40%
Reduction of scrap rate: eliminate human error → yield rate increased to 99%+
3. Expanded processing capabilities
Processable inclination range: -30°~+110° (±15° only without RTCP)
Minimum curvature radius: up to 0.3 times the tool diameter
6).Industry application example: Aerospace impeller processing
1. Processing challenges
Material: Inconel 718 high-temperature alloy (hardness HRC 45)
Features: Twisted blade spacing ≤ 3mm, blade crown surface curvature changes dramatically
2. RTCP solution
(1) Tool path planning:
(2) Dynamic compensation:
(3）Results comparison:
7).Technology development trends of RTCP
1. RTCP+AI adaptive machining
Real-time monitoring of cutting force → Dynamic optimization of tool axis vector
Case: GF Machining's Adaptive Machining system
2. Collaborative RTCP (C-RTCP)
Multi-machine TCP synchronization (such as dual-spindle engraving machine)
Application: Large wind turbine blade mold processing
3. Digital twin integration
Preview RTCP compensation effect in a virtual environment
Machine Simulator module in Siemens NX CAM
8). Precautions for implementing RTCP
1. Machine tool calibration requirements
The position of the pivot point of the rotating axis needs to be checked regularly (laser tracker calibration)
Temperature compensation: environmental changes of ±1℃ lead to 0.01mm/100mm error
2. Tool management specifications
Tool length measurement error needs to be <0.005mm (affects compensation accuracy)
It is recommended to use a radio frequency identification (RFID) tool system
3. Safety protection mechanism
Set RTCP space boundaries (to prevent over-travel collision)
Real-time monitoring of each axis following error (threshold ≤0.02mm)
Conclusion:
RTCP technology value triangle model:
Precision
/ \
/ \
efficiency ─── Flexibility
(Reduce clamping)
Through dynamic tool center point control, RTCP simultaneously optimizes the three core indicators of five-axis machining, becoming an essential technology for the manufacture of complex parts.
RTCP technology improves the processing capability of five-axis engraving machines from "movable" to "precision controllable", and solves the geometric distortion problem caused by rotational motion through dynamic spatial coordinate mapping. With the enhancement of real-time computing capabilities and the optimization of motion control algorithms, RTCP is evolving from a basic function to the core engine of intelligent processing, providing irreplaceable technical support for the processing of complex parts in the field of high-end manufacturing. In the context of industrial upgrading such as aerospace, precision medicine, and new energy, mastering the deep application capabilities of RTCP has become a key yardstick for measuring the processing level of five-axis equipment.
FAQ guide：
Q1: What is RTCP?
A1:
RTCP = Rotational Tool Center Point (rotational tool center point control), also known as TCPM (Tool Center Point Management) or TCPC (Tool Center Point Control) in the industry.
Q2: What core problems does RTCP solve in 5 axis cnc machining?
A2:
Eliminate tool offset caused by rotary axis movement:
Rotation axis angle θ → tool tip displacement ΔL = rotation radius R × (1-cosθ)
▸ Without RTCP: The actual cutting point deviates from the programmed path → overcutting/undercutting
▸ With RTCP: The system automatically compensates ΔL → The tool tip strictly follows the command coordinates
Q3: How does RTCP improve machining accuracy?
A3 Through the triple compensation mechanism:
Q4: Which five-axis structures must enable RTCP?
A4
Dual turntable structure (BC axis on the worktable)
Swing head + turntable (spindle A axis + worktable C axis)
Orthogonal swing head structure (spindle A/C axis linkage)
Q5: What impact does RTCP have on programming?
A5 Subversively simplifies the process:
Traditional programming CAM pre-calculates rotation coordinates
Generates lengthy G code
RTCP programming
CAM outputs tool position point + tool axis vector
System automatically solves
Code volume reduced by 50%
Q6: How to determine whether the machine system supports RTCP?
A6 Key identification method:
CNC system model: Syntec 610ma-e or more advanced versions/Siemens 840D/Heidenhain iTNC640/Fanuc 30i-B+
G code command:
gcodeG43.4 from Syntec 5 axis system; Fanuc RTCP activation command TRAORI; Siemens five-axis transformation command
Hardware configuration: rotary axis encoder resolution ≤ 0.001°
Q7: Will RTCP reduce processing efficiency?
A7 On the contrary:
Q8: Common pitfalls in RTCP implementation?
A8 Frequent fault points:
Machine calibration missing → Pivot point offset not calibrated → Compensation error amplified
Tool measurement error → Tool length input deviation 0.1mm → Workpiece scrapped
Overload collision →
CNC 5 axes (including 5 axis CNC Router, 5 axis cnc machining center etc) achieve complex surface processing through three linear axes (X/Y/Z) and two rotary axes (two of A/B/C). In traditional 3 axis processing, the tool center point (TCP) path is consistent with the programmed path; but when the 5 axis are linked, the movement of the rotary axis will change the spatial orientation of the tool relative to the workpiece, resulting in:
- The actual tool path deviates from the programmed path
- The processing accuracy decreases
- The workpiece needs to be repositioned frequently
RTCP (Rotational Tool Center Point Control) is the core technology created to solve this problem. Its core idea:
"No matter how the rotary axis moves, the control system always dynamically compensates the tool center point position so that it strictly follows the programmed path."
1. Technical principles and mathematical foundations of RTCP in CNC
1). Core algorithm: coordinate transformation and kinematic inverse solution
The essence of RTCP is to map the tool path from the workpiece coordinate system (programming coordinate system) to the machine tool motion coordinate system through real-time coordinate transformation
2). Dynamic compensation process:
Read the TCP coordinates and tool direction of the current programming point
Calculate the actual tool tip position offset according to the rotation axis angle
Adjust the linear axis position compensation offset in real time
Ensure that the tool tip is always at the programming position
3). Mathematical example (simplified model):
Assume that the rotary table (B axis) rotates at an angle of θ and the tool arm length is L:
Without RTCP: Tool tip offset = L × (1 - cosθ)
After enabling RTCP: Z axis automatically moves down to compensate ΔZ = L × (1 - cosθ)
Figure 1: RTCP compensation algorithm flow chart
2). Implementation of the core functions of RTCP in the 5 axis CNC machine
1. Dynamic locking of the tool center point
Function: No matter how the A/B/C axis rotates, the tool tip coordinates (X, Y, Z) strictly follow the G code path
Realization: The CNC system solves the Cartesian coordinate offset caused by the rotation in real time and offsets it through the linear axis linkage
2. Tool direction vector control
Function: Keep the tool axis consistent with the surface normal (key for engraving steep side walls)
Realization: Dynamically adjust the rotation axis angle according to the surface model data
3. Elimination of non-linear errors
Problem: The non-orthogonal structure of the rotation axis (such as swing head + turntable) causes motion coupling errors
RTCP solution: Preset machine tool geometric parameters (such as axis offset, pivot distance) in the kinematic model
4. Simplified program writing
Traditional method: The rotation axis position needs to be pre-calculated in the CAM software → The program is lengthy and error-prone
RTCP mode: Directly output the tool path (XYZ + tool axis vector) → G code volume is reduced by 50%+
3). Typical application of RTCP in 5 axis cnc wood router
1. Complex wooden surface engraving
| Application | RTCP function |
| Turbine blade finishing | Maintain a constant cutting angle to avoid overcutting |
| Relief Sculptures Art Surface | Realize reverse feed to improve detail clarity |
| Human skeleton medical model | Processing of negative angle areas to reduce secondary clamping |
Problem: Tool elongation causes rigidity to decrease, and the side wall is prone to vibration
RTCP solution: By adjusting the tool inclination angle, side milling is converted to end milling (improving rigidity)
3.Multi-angle feature processing
4). RTCP system implementation architecture
1. Hardware requirements
| Components | Requirements |
| System | Support RTCP function (such as Siemens 840D,Syntec 610MA-E5） |
| Servo driver | High response frequency (>1kHz) |
| Rotary shaft encoders | Resolution ≤ 0.001° |
| Linear axis scales | Closed-loop feedback (accuracy ±0.005mm) |
2. Software workflow
• Input: 3D model of workpiece
• CAM stage: Generate CL file containing tool position (XYZ) and tool axis vector (I, J, K)
• Post-processing: Convert to G code (such as G43.4 to open RTCP mode)
• CNC system:
lAnalyze tool axis vector
lReal-time kinematics inversion
lGenerate servo instructions for each axis
3. Key CNC instructions gcode
G54 ; Workpiece coordinate system
G43.4 H01 ; Enable RTCP (Tool Length Compensation Mode)
G01 X100 Y50 Z-10 I0 J0 K1 F500 ; Linear interpolation (K=1 means vertical downward)
Picture 3：RTCP control system architecture
+-------------------+ +-------------------+ +-------------------+
| CAMsoftware | | cnc system | | servo system |
| (create XYZ+IJK) |---->| RTCP mode |---->| (Run compensatory movements) |
| | | ┌─────────────┐ | | |
| | | │ Kinematics Solver │ | | X axis：±0.005mm |
| | | │ Real-time calculationΔXYZ │ | Y axis：±0.005mm |
+-------------------+ | └─────────────┘ | | Z axis：±0.003mm |
| ┌─────────────┐ | | A axis：±0.001° |
| │ Tool radius compensation│ | B axis：±0.001° |
| └─────────────┘ | +-------------------+
+-------------------+
▲
│
+-------------------+
| Linear scale feedback |
| (Closed-loop position detection) |
+-------------------+
5). Technical advantages and economic benefits brought by RTCP
1. Accuracy improvement comparison
| index | NO RTCP | RTCP WORK | Improvement |
| Position accuracy | ±0.1mm | ±0.02mm | 80% |
| Surface profile error | >0.3mm | <0.05mm | 83% |
| Visibility of cutting marks | YES | LITTLE | - |
2. Efficiency optimization data
Programming time reduction: reduce manual calculation of rotary axis position → save 30% CAM time
Processing cycle compression: avoid repositioning → complex workpiece processing speed increased by 40%
Reduction of scrap rate: eliminate human error → yield rate increased to 99%+
3. Expanded processing capabilities
Processable inclination range: -30°~+110° (±15° only without RTCP)
Minimum curvature radius: up to 0.3 times the tool diameter
6).Industry application example: Aerospace impeller processing
1. Processing challenges
Material: Inconel 718 high-temperature alloy (hardness HRC 45)
Features: Twisted blade spacing ≤ 3mm, blade crown surface curvature changes dramatically
2. RTCP solution
(1) Tool path planning:
- lThe tool axis vector changes continuously with the surface normal
- lThe tilt angle is controlled at 10°~25° to avoid interference
(2) Dynamic compensation:
- lZ-axis automatically compensates ±1.2mm when B-axis rotates
- lLinear speed remains constant at 35m/min
(3）Results comparison:
- lSurface roughness: Ra 0.8μm → 0.4μm
- lTool life: increased from 45 minutes to 110 minutes
7).Technology development trends of RTCP
1. RTCP+AI adaptive machining
Real-time monitoring of cutting force → Dynamic optimization of tool axis vector
Case: GF Machining's Adaptive Machining system
2. Collaborative RTCP (C-RTCP)
Multi-machine TCP synchronization (such as dual-spindle engraving machine)
Application: Large wind turbine blade mold processing
3. Digital twin integration
Preview RTCP compensation effect in a virtual environment
Machine Simulator module in Siemens NX CAM
8). Precautions for implementing RTCP
1. Machine tool calibration requirements
The position of the pivot point of the rotating axis needs to be checked regularly (laser tracker calibration)
Temperature compensation: environmental changes of ±1℃ lead to 0.01mm/100mm error
2. Tool management specifications
Tool length measurement error needs to be <0.005mm (affects compensation accuracy)
It is recommended to use a radio frequency identification (RFID) tool system
3. Safety protection mechanism
Set RTCP space boundaries (to prevent over-travel collision)
Real-time monitoring of each axis following error (threshold ≤0.02mm)
Conclusion:
RTCP technology value triangle model:
Precision
/ \
/ \
efficiency ─── Flexibility
(Reduce clamping)
Through dynamic tool center point control, RTCP simultaneously optimizes the three core indicators of five-axis machining, becoming an essential technology for the manufacture of complex parts.
RTCP technology improves the processing capability of five-axis engraving machines from "movable" to "precision controllable", and solves the geometric distortion problem caused by rotational motion through dynamic spatial coordinate mapping. With the enhancement of real-time computing capabilities and the optimization of motion control algorithms, RTCP is evolving from a basic function to the core engine of intelligent processing, providing irreplaceable technical support for the processing of complex parts in the field of high-end manufacturing. In the context of industrial upgrading such as aerospace, precision medicine, and new energy, mastering the deep application capabilities of RTCP has become a key yardstick for measuring the processing level of five-axis equipment.
FAQ guide：
Q1: What is RTCP?
A1:
RTCP = Rotational Tool Center Point (rotational tool center point control), also known as TCPM (Tool Center Point Management) or TCPC (Tool Center Point Control) in the industry.
Q2: What core problems does RTCP solve in 5 axis cnc machining?
A2:
Eliminate tool offset caused by rotary axis movement:
Rotation axis angle θ → tool tip displacement ΔL = rotation radius R × (1-cosθ)
▸ Without RTCP: The actual cutting point deviates from the programmed path → overcutting/undercutting
▸ With RTCP: The system automatically compensates ΔL → The tool tip strictly follows the command coordinates
Q3: How does RTCP improve machining accuracy?
A3 Through the triple compensation mechanism:
| type | Compensation | Accuracy improvement effect |
| Rotational centrifugal offset | ΔZ=R(1-cosθ) | Eliminate ±0.5mm level error |
| Tool head pivot error | ΔX=L·tanα | Reduce lateral deviation>80% |
| Nonlinear coupling error | Real-time solution of movement models | Surface profile accuracy up to 0.02mm |
Q4: Which five-axis structures must enable RTCP?
A4
Dual turntable structure (BC axis on the worktable)
Swing head + turntable (spindle A axis + worktable C axis)
Orthogonal swing head structure (spindle A/C axis linkage)
Q5: What impact does RTCP have on programming?
A5 Subversively simplifies the process:
Traditional programming CAM pre-calculates rotation coordinates
Generates lengthy G code
RTCP programming
CAM outputs tool position point + tool axis vector
System automatically solves
Code volume reduced by 50%
Q6: How to determine whether the machine system supports RTCP?
A6 Key identification method:
CNC system model: Syntec 610ma-e or more advanced versions/Siemens 840D/Heidenhain iTNC640/Fanuc 30i-B+
G code command:
gcodeG43.4 from Syntec 5 axis system; Fanuc RTCP activation command TRAORI; Siemens five-axis transformation command
Hardware configuration: rotary axis encoder resolution ≤ 0.001°
Q7: Will RTCP reduce processing efficiency?
A7 On the contrary:
| Type | No RTCP | With RTCP | Improvement |
| Switching time | 25s/time | 0秒 | 100% |
| Number of clamping | 3-5times | 1次 | 70%↑ |
| Curved surface processing efficiency | 35cm³/min | 60cm³/min | 71%↑ |
Q8: Common pitfalls in RTCP implementation?
A8 Frequent fault points:
Machine calibration missing → Pivot point offset not calibrated → Compensation error amplified
Tool measurement error → Tool length input deviation 0.1mm → Workpiece scrapped
Overload collision →
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