1. Description of the problem and scope

This guide is intended to solve the problem of poor surface quality that occurs during CNC machining. Poor surface quality can manifest itself in the form of increased roughness, changes in the shape of the product, deviation from design parameters or surface damage. This problem can occur on various types of equipment, including lathes, milling machines, grinding machines, and other CNC machines. The problem is classified as critical because it can lead to product rejection, rework costs, and failure to meet production requirements.

2. Preventive measures

Use of protective equipment: When working with metals that have a high temperature or grinding cutters, it is necessary to use work gloves, glasses, boots and special clothing. It is important to ensure the cleanliness of the workplace and the use of a special measuring tool.

Power Outage: Perform a lockout/tagout (LOTO) procedure before starting any measurements or restoring equipment to avoid unexpected power outages or restoration.

Recovery of protective elements: Before performing any operation on the equipment, check whether there is stored energy in the spindle, hydraulic actuator or other components. Use the appropriate tools to recover these items.

3. Necessary diagnostic tools

4. First review and checklist

5. Systematic diagnostic flow

1. Poor surface quality
   1. Check spindle vibration
   2. If the vibration is higher than 5 mm/s
      1. Check the spindle deviation
      2. If the deviation exceeds 0.02 mm
         1. Spindle restoration or replacement
   3. If the vibration is higher than 5 mm/s
      1. Check the condition of the tool
      2. If the tool is exhausted
         1. Replacement of the tool

6. Matrix of causes of defects

7. Analysis of the causes of defects

7.1. Exhaustion of the tool

Tool wear occurs due to improper use, high temperature conditions, insufficient cooling effect or selection of incorrect cutting parameters. Failure to correct this problem may result in incorrect processing, deviation from design parameters, or damage to the equipment.

Diagnosis: Measure the distance between the tool and the workpiece. If the distance exceeds 0.05 mm, this may be a sign of exhaustion.

Solution: Replace the tool or select a tool with higher fatigue resistance.

7.2. Spindle vibration

Spindle vibration can be caused by worn bearings, spindle deflection, or improper use of the electronic control system. Vibration can lead to a decrease in surface quality, an increase in roughness, or a deviation from the design parameters.

Diagnosis: Measure spindle vibration. If it exceeds 5 mm/s, it may be a sign of vibration imbalance.

Solution: Replace the spindle bearings or rebuild the spindle.

7.3. Spindle deflection

Spindle deflection occurs due to misuse, worn bearings, or lack of proper adjustment. Deviation can result in incorrect cuts, deviation from design parameters or equipment damage.

Diagnosis: Measure the spindle deviation. If the deviation exceeds 0.02 mm, this may be a sign of deviation.

Solution: Rebuild the spindle or replace it.

7.4. Incorrect cutting parameters

Incorrect cutting parameters can lead to tool fatigue, vibration, reduced surface quality or deviation from design parameters. It is important to use parameters that meet the requirements of the material, equipment and technology.

Diagnosis: Check the cutting parameters. If they do not meet the standards, this may be a sign of the wrong choice.

Solution: Choose cutting parameters that match the processing requirements.

8. Step-by-step troubleshooting procedures

8.1. Exhaustion of the tool

1. Measure the distance between the tool and the workpiece. If the distance exceeds 0.05 mm, the tool is exhausted.
2. Replace the tool or select a tool with higher fatigue resistance.
3. Check whether the cutting parameters meet the requirements.

8.2. Spindle vibration

1. Measure spindle vibration. If it exceeds 5 mm/s, the spindle vibrates.
2. Replace the spindle bearings or rebuild the spindle.
3. Check if the electronic control system meets the requirements.

8.3. Spindle deflection

1. Measure the spindle deflection. If the deviation exceeds 0.02 mm, the spindle is deviated.
2. Rebuild the spindle or replace it.
3. Check if the spindle tuning is correct.

8.4. Incorrect cutting parameters

1. Check the cutting parameters. If they do not meet the standards, this may be a sign of the wrong choice.
2. Select the cutting parameters that match the processing requirements.
3. Check if the electronic control system meets the requirements.

9. Prevention networks

10. Spare parts and components

For parts or more information visit: https://www.unitecd.com/e-catalog/

11. Links

• Standards: DSTU 3031:2006, EN 60204-1, ISO 10426-1
• Reference materials: Manufacturers' catalogs, technical passports, technical manuals
• Special Guides: Spindle Restoration Guide, Tool Selection Guide

1. Description of the problem and scope

This manual is dedicated to diagnosing and correcting CNC machine positioning errors caused by screw backlash, encoder shaft failure, thermal compensation failure, and wrong servo setting. The problem can occur in various types of production: automotive, aviation, food, chemical and power plants. According to DSTU 3015:2015, EN ISO 10216-1:2012 and CE standards, compliance with technical parameters is critical to ensure manufacturing accuracy. The conditions are considered critical if there are deviations from the set position by more than 0.01 mm or periodic gray failures occur.

2. Safety and Warnings

Important: Before starting diagnostics, perform a lockout/tagout (LOTO) procedure to disconnect the power supply and disconnect the drives. Use protective glasses, gloves and special clothing if there is a risk of electric shock or mechanical elements. Check for stored energy in the syrvo system, especially after a power outage. Accidental activation or deactivation may result in personal injury or equipment damage.

3. Necessary diagnostic tools

4. First review and checklist

5. Systematic diagnostic scheme

1. Symptom: Positioning deviation from the specified value.
   1. Diagnosis: Measure the deviation with a thermal camera and a micrometer.
      1. Result: Deviation < 0,01 мм – ймовірна несправність енкодерної фідачки.
         1. Diagnostic test: Measure the voltage and current on the encoder probe.
         2. Expected result: Deviation in voltage > 5% or in current > 10% - possible malfunction.
2. Symptom: Screw vibration during operation.
   1. Diagnosis: Use a vibration analyzer to measure vibration characteristics.
      1. Result: Vibration > 10 mm/s – likely screw or gear failure.
         1. Diagnostic test: Measure the propeller backlash.
         2. Expected result: Backlash > 0.02 mm - correction required.
3. Symptom: Unstable positioning during thermal changes.
   1. Diagnosis: Measure the temperature in the working area and check for thermal compensation.
      1. Result: The temperature changes by more than 5°C - probable lack of thermal compensation.
         1. Diagnostic test: Check gray settings for thermal compensation.
         2. Expected result: No setting - must be set.
4. Symptom: Unstable operation of the relay.
   1. Diagnosis: Measure the current and voltage in the relay circuit.
      1. Result: Deviation in current > 10% - probable wrong setting.
         1. Diagnostic test: Check gray settings in setup menu.
         2. Expected result: Incorrect parameters - needs to be adjusted.

6. Matrix for finding reasons

7. Analysis of root causes

7.1 Malfunction of the encoder file

An error in the encoder file can occur due to damaged cables, moisture or lack of power supply. According to EN ISO 10216-1:2012, the voltage and current measurement in the encoder box should be within 0-200 V and 0-200 mA. If the deviation exceeds 5% of the nominal values, this may be a sign of a lack of power supply or corrosion.

7.2 Reversal of the screw

Propeller backlash is caused by damage to the propeller, lack of lubrication, or improper adjustment. According to DSTU 3015:2015, the allowable backlash of the screw should not exceed 0.02 mm. If the backstroke exceeds this value, positioning errors may accumulate.

7.3 Errors in gray

Incorrect tuning of the servo can lead to failures in positioning. The EN ISO 10216-1:2012 standard requires that the deviation in the gray current does not exceed 10% of the nominal values. If the deviation exceeds this value, it may be due to incorrect settings or lack of compensation.

7.4 Lack of thermal compensation

Thermal compensation conforms to EN ISO 10216-1:2012 to ensure positioning stability with temperature changes. If the lack of thermal compensation results in temperature changes of more than 5°C, positioning errors may accumulate.

8. Correction sequence

8.1 Compensation for the malfunction of the encoder file

1. Power down the system and perform the LOTO procedure.
2. Measure the voltage and current on the encoder probe. If the deviation exceeds 5%, replace the encoder file.
3. Check the cables for corrosion or damage.
4. Turn on the power again and check the positioning.

8.2 Correcting the reverse movement of the screw

1. Use a micrometer to measure the screw backlash.
2. If backlash > 0.02 mm, adjust or replace screw.
3. Check the lubrication of the screw and gears.
4. Measure the return stroke again and check the positioning.

8.3 Gray settings

1. Measure the current in gray and compare with the nominal values.
2. If the deviation is > 10%, adjust gray in the setup menu.
3. Check the thermal compensation settings.
4. Measure the current again and check the positioning.

8.4 Installation of thermal compensation

1. Measure the temperature in the work area.
2. If the temperature changes by more than 5°C, set thermal compensation in the setup menu.
3. Check the thermal compensation settings.
4. Measure the temperature again and check the positioning.

9. Prevention

10. Spare parts and components

Go to the UNITEC-D catalog

11. Links

• DSTU 3015:2015 – Positioning accuracy and stability
• EN ISO 10216-1:2012 – Positioning accuracy of CNC machines
• CE standard - Technical requirements for electrical equipment
• UkrSEPRO – Electrical safety standards
• UNITEC-D Maintenance Guide – Additional maintenance recommendations