BALLBAR AND KGM
The Ballbar test, also known as a circularity test, is one of the most effective methods for quickly assessing the geometric accuracy of CNC machines. It is a diagnostic tool that detects axis performance deviations and helps identify the root causes of machining errors—before they lead to major inaccuracies or product defects.
What is a Ballbar test?
A Ballbar is a precision measuring device that records deviations of tool movement from an ideal circular path. The test involves the CNC machine performing a circular interpolation while the Ballbar device measures the distance between two fixed points in real time.
The measurements generate a report and graph that reveal:
- Geometric errors (e.g., guideway misalignment, backlash)
- Servo tuning issues
- Errors caused by friction or mechanical play
- Dynamic faults during acceleration/deceleration
Key Advantages
- Fast testing (completed in minutes)
- No machine disassembly required
- Clear graphical report and diagnostics
- Detects faults hard to identify by conventional methods
- Enables historical trend comparisons (wear analysis)
- Supports servo loop tuning and axis motion optimization
Ballbar testing is an excellent diagnostic step before and after laser calibration, allowing quick verification of correction effectiveness.
When to use it?
The Ballbar test is ideal for:
- Regular preventive CNC maintenance (e.g., annually)
- Diagnostics after collisions or mechanical incidents
- Checking quality of machine assembly or retrofit
- Monitoring long-term machine stability (trend tracking)
Who benefits from this service?
- Toolmakers and high-precision workshops
- Automotive, aerospace, and medical device industries
- Anyone needing verified machine accuracy
- Service providers and system integrators
KGM
The KGM test (Kreis- und Gitter-Messgerät – Circle and Grid Encoder) is an advanced non-contact motion testing system for CNC machines in two axes (e.g., XY), developed by HEIDENHAIN. This test precisely and in real time evaluates both the dynamic and geometric characteristics of tool movement, without mechanical contact with the machine table.
KGM represents one of the most sensitive methods for detecting inaccuracies on modern CNC machines—especially where high repeatability and micron-level accuracy are required.
What is the KGM test?
The KGM system uses a precise reference grid and optical position sensing to detect:
- Inaccuracies in linear and circular movements
- Axis oscillations or vibrations
- Sinusoidal errors, tremors, and stick-slip effects
- Dynamic responses to changes in speed or direction
Testing is performed without physical contact, and can be executed at different speeds and with a variety of motion patterns.
When to use the KGM test?
- When the highest 2D machining accuracy is needed
- After mechanical overhaul or retrofit of a CNC machine
- To validate servo axis performance or system linearity
- As part of quality control in ISO-certified environments
Advantages of the KGM system
- Extremely high resolution and repeatability
- Detects micro deviations other tests may miss
- No wear or mechanical contact
- Can test circular, rectangular, spiral, or custom paths
- Standard tool for accuracy certification in aerospace, toolmaking, and precision manufacturing
