1. Scope & Purpose
This technical maintenance manual details the preventive and corrective measures for slideway lubrication systems of CNC machine tools. It covers central components such as lubricating oil pumps, filter units and oil level monitoring devices. The primary goal of this maintenance is to ensure the operational accuracy and service life of the CNC machines, to minimize unexpected failures and to ensure compliance with production standards, such as those required in DIN EN ISO 230-1 for the geometric accuracy of machine tools.
Regular maintenance is critical to ensure continuous and correct lubrication of the slideways, thereby reducing friction and wear. This manual is designed to be used during scheduled maintenance intervals and when troubleshooting problems related to the lubrication system.
2. Safety precautions
ATTENTION: Danger from moving parts, electrical energy and hot liquids!
- Lockout/Tagout (LOTO): Before starting any work on the lubrication system, the CNC machine must be completely de-energized in accordance with VDE 0105-100 and secured against being switched on again. All energy-carrying lines, hydraulic and pneumatic systems must be drained and secured.
- Personal protective equipment (PPE): It is mandatory necessary to wear safety glasses (EN 166), chemical-resistant protective gloves (EN 374, to protect against oils and cleaning liquids) and safety shoes (EN ISO 20345).
- Umgang mit Schmierstoffen: Schmieröle können Haut- und Augenreizungen verursachen. Avoid direct contact. In case of skin contact, clean thoroughly with soap and water. Bei Augenkontakt sofort und ausgiebig spülen und ärztlichen Rat einholen. Die Sicherheitsdatenblätter (SDS) der verwendeten Schmierstoffe sind zu beachten.
- Brandgefahr: Schmieröle sind brennbar. Keep open flames and ignition sources away. Suitable fire extinguishing agents (e.g. foam or CO2 extinguishers) must be available.
- Restdruck: Systeme können Restdruck enthalten. Before opening lines or filters, ensure that the system is depressurized.
3. Required Tools & Materials
The table below lists the critical tools and materials needed for efficient and safe maintenance of the lubrication system.
| Tool/Material | Specification/Type | quantity | Notes |
|---|---|---|---|
| Torque wrench | 5 – 50 Nm, calibrated according to DIN EN ISO 6789 | 1 | For precise tightening of screw connections |
| Torque wrench | 50 – 200 Nm, calibrated according to DIN EN ISO 6789 | 1 | For larger screw connections |
| multimeter | CAT III 600V, DIN EN 61010-1 | 1 | For electrical measurements on pump motors/controllers |
| Vernier caliper | 0 – 150 mm, accuracy 0.02 mm, DIN 862 | 1 | For measuring seals and gap dimensions |
| Allen key set | Metric, hardened steel | 1 sentence | Standard sizes |
| Screwdriver set | slot, cross slot (PH, PZ) | 1 sentence | Standard sizes |
| Combination/open-end wrench set | Metric (e.g. 8 – 32 mm) | 1 sentence | For loosening and tightening screw connections |
| collection pan | Min. 10 liter capacity, chemical resistant | 1 | For collecting used oil |
| Industrial cleaning wipes | Low-lint, oil-resistant | 1 package | For cleaning components and surfaces |
| Replacement filter element | According to OEM specification (e.g. 10-25 µm), UNITEC category FILTER | 1-2 | Suitable for the lubrication system |
| Hydraulic/slideway oil | According to OEM specification (e.g. ISO VG 68 or ISO VG 100 according to DIN 51517-3), UNITEC category LUBRICANTS | As required (at least 5 liters) | Make sure it is compatible with the existing oil |
| O-rings / seals | According to OEM specification, UNITEC category SEALS | As required | For filter housings and pump flanges |
| Cleaner for metal parts | Industrial cleaner, biodegradable, residue-free | 1 spray bottle | For cleaning metal filters and housings |
| Drain hose with clamp | Oil-resistant, approx. 1 meter long | 1 | For clean draining of used oil |
4. Pre-maintenance inspection checklist
This checklist serves to systematically record the system status before detailed maintenance work begins. Careful execution is essential for identifying potential problems.
| Item | Check | Acceptance criteria | Notes |
|---|---|---|---|
| Oil level in the container | Visual inspection on the sight glass | Between min and max marking (ideally 75-90% filled) | Below minimum requires immediate refill |
| External leaks | Visual inspection of pump, lines, screw connections | No visible oil leaks or oil stains | Leakage of a few drops per day is not acceptable |
| Pump noise | Hearing test during short-term operation (under supervision) | Regular, inconspicuous operating noise | Loud, clattering, whistling or irregular noises are a warning signal |
| Filter clogging indicator | Visual inspection of the filter housing | Display in the green area or on “clean” | Red indicator or “clogged” requires immediate filter change |
| Condition of the hoses/pipes | Visual and tactile inspection for damage | No cracks, kinks, porosity or deformation | Porous hoses lead to pressure loss and leaks |
| Electrical connections of the pump | Visual inspection for tightness and corrosion | Connections tight, no corrosion, insulation intact | Loose connections can lead to failures |
| System pressure (manometer) | Reading the pressure gauge during operation | Within the range specified by the manufacturer (e.g. 2-5 bar) | Pressure out of range indicates a problem |
| Oil quality (visual inspection) | Testing a small oil sample for cloudiness, discoloration, foreign bodies | Clear, honey colored (typical of new oil), free of particles or water | Cloudiness, dark discoloration or water accumulation require oil change |
5. Step-by-step instructions
This guide will systematically guide you through the maintenance of the CNC slideway lubrication system. Have all safety instructions and tools ready.
5.1 Preparation & Safety
Machine Shutdown & Backup: Perform the full LOTO procedure for the CNC machine. Make sure all energy sources are isolated and secured. Check that the electrical components are free of voltage using a multimeter (e.g. 0V AC/DC on the pump supply).
Put on PPE: Put on the prescribed personal protective equipment (safety glasses, protective gloves, safety shoes).
Work area Preparation: Place the collecting pan under the lubricating oil container and the filter units to catch any oil that may escape. Have cleaning wipes ready.
5.2 Oil level check and refilling
Oil level Check: Check the oil level on the sight glass of the reservoir. The level should be between the min and max marks.
Oil refill: If the oil level is below the recommended 75% of the sight glass range, refill the container with the slideway oil specified by the machine manufacturer (e.g. ISO VG 68 or ISO VG 100, according to DIN 51517-3). The level should reach 80-90% of the sight glass. Use a clean funnel for this.
- Common mistake: Mixing different types of oil. This can lead to chemical reactions, foaming and loss of lubricating properties. Strictly avoid this!
Close lid: Close the container filler cap tightly to prevent contaminants from entering.
5.3 Pump inspection
The lubricating oil pump is the heart of the system. A detailed inspection is mandatory.
Visual inspection of the pump:
- Check the pump housing for cracks, deformation or signs of overheating.
- Check all connections (electrical, oil) for tightness and leaks.
- Check the cable insulation for damage.
Functional test (briefly under supervision):
- After LOTO is briefly lifted and the work area is safe, briefly turn on the machine to activate the pump.
- Observe whether the pump starts and delivers oil (visually at lubrication points or pressure gauge).
- Apply LOTO again immediately.
- Common error: Let the pump run for a long time without checking. In the event of defects, this can lead to consequential damage.
Pressure measurement (if pressure gauge is available):
- Observe the system pressure on the pressure gauge during the short functional test. The pressure should be stable and within the range specified by the OEM (typically 2-5 bar, maximum 10 bar).
- Deviations of ±10% from the target pressure must be examined.
Noise analysis: Listen for unusual noises from the pump (e.g. loud humming, rattling, grinding, or cavitation noises – a high-frequency whistling or crackling noise). A constant, quiet operating noise is normal.
- Common Error: Ignoring unusual noises. This may indicate beginning pump wear or air intrusion.
5.4 Filter maintenance
The oil filter is critical for the cleanliness of the lubricating oil and the protection of the slideways.
Pressure relief & dismantling the filter:
- Make sure the system is depressurized (according to LOTO).
- Carefully loosen the filter housing screws using the appropriate wrenches. Have the drip pan ready as residual oil can escape.
- Remove the filter housing and the old filter element.
- Common error: Open the filter housing under pressure. This can result in oil splashes and injury.
Cleaning/replacing the filter element:
- Reusable filters (e.g. metal mesh filters): Clean the filter element thoroughly with a suitable industrial cleaner for metal parts. Then rinse it with clean lubricating oil or cleaning fluid without leaving any residue and allow it to dry completely. Check the filter fabric for damage.
- Disposable filters (e.g. paper, fleece filters): Replace the old filter element with a new, OEM-specified filter element with the correct filter fineness (e.g. 10-25 µm).
- Common error: Not cleaning the reusable filter thoroughly enough or continuing to use a damaged filter. This leads to inadequate filtration.
Mounting the filter:
- Thoroughly clean the filter housing inside and out.
- Insert a new filter element. Always use new O-rings and seals. Lightly lubricate the seals with clean lubricating oil to ease assembly and prevent damage.
- Assemble the filter housing and tighten the screws crosswise with the torque wrench. Please note the torques specified by the manufacturer (typically 20-25 Nm for housing screws, 10-15 Nm for small filters).
- Common Error: Reusing gaskets or not tightening them sufficiently. This leads to leaks.
5.5 Line and nozzle check
Checking the lubrication lines: Inspect all lubrication lines (e.g. PA hoses 4mm, 6mm or steel lines) for:
- Visible damage, cracks, abrasions or creases.
- Brittleness or porosity, especially at bends and connections.
- Fixed attachment along the machine.
Inspection of lubrication nozzles/distributors: Check all lubrication nozzles and distributors for:
- Blockages or contamination.
- Fixed installation at the lubrication points of the slideways.
- Leakage of lubricating oil during a short-term system test (see 5.7).
Cleaning/replacement: Damaged lines or clogged nozzles must immediately be replaced or cleaned. A blockage can be cleared with compressed air (CAUTION: Wear safety glasses!) or a fine wire. If there are stubborn blockages, the nozzle must be removed and cleaned or replaced.
5.6 Electrical component testing (in the event of malfunctions or as part of major maintenance)
Voltage test: Check the voltage supply to the pump motor using a multimeter. Measure the voltage directly at the pump connection (e.g. 24V DC or 230V AC, depending on the system). ATTENTION: Only qualified personnel can work under voltage!
Fuse check: Check the relevant fuses in the control cabinet for the pump control for continuity (Ohm measurement when voltage-free).
Motor resistance measurement: Measure the winding resistance of the pump motor when the voltage is off. Compare the measured value with the manufacturer's information. Deviations can indicate engine damage.
- Common error: Working on electrical systems without LOTO. Danger to life!
5.7 System test run & venting
LOTO Unlock & System Start: After all work is completed, remove the LOTO fuses. Start the CNC machine and lubrication system.
Bleeding the system: If air has gotten into the system (e.g. after an oil change or pump overhaul), it must be bled. This often happens automatically through system operation; For manual bleed screws, open them carefully until bubble-free oil comes out, then close them again.
Checking the lubrication points: Observe all lubrication points on the slideways for at least 5 minutes. An even oil leak must be visible. Typical discharge quantities per lubricating pulse are 0.05 – 0.2 ml.
Leaks Check: Check all screw connections, seals and lines again for leaks. In particular, check the filter housing and the pump connections.
Pump noise Check: Listen again to the operating noise of the pump, it should now be quiet and stable.
Filter display Check: The filter contamination indicator must be in the green area.
6. Post-maintenance verification checklist
This checklist is used for mandatory functional testing and documentation after maintenance work has been completed.
| Test/Checkpoint | Expected result | Actual result | Pass/Fail |
|---|---|---|---|
| Oil level in the container | In the upper area of the sight glass (80-90%) | ||
| No visible leaks | All connections and sealing surfaces are dry | ||
| Pump function noise | Quiet, even, free of unusual noises | ||
| System pressure | Stable in the target range (e.g. 2-5 bar) | ||
| Lubrication nozzle delivery | Oil comes out evenly at all lubrication points | ||
| Filter clogging indicator | In the green / “clean” | ||
| Electrical connections | Safe and secure (visually checked) | ||
| General cleanliness | Work area and machine cleaned, used oil disposed of |
7. Troubleshooting
This table provides a quick reference for the most common slideway lubrication system problems and how to resolve them.
| Symptom | Probable cause | Corrective action |
|---|---|---|
| No oil leakage at lubrication points | Pump does not deliver (defective, clogged) Filter clogged Line(s) blocked/kinked Oil level too low System not bled |
Check/replace pump, check electrical supply line Clean/replace filter Check line(s) for damage/kink, clean Refill oil Bleede system |
| Low/fluctuating system pressure | Air in the system Pump worn/defective Filter very dirty Leaks in the system Pressure relief valve defective/incorrectly set |
Bleed system Check/replace pump Clean/replace filter Look for and seal leaks Check/adjust/replace pressure relief valve |
| Oil leaks | Loose screw connections Damaged seals/O-rings Cracks in lines/housings Incorrect assembly of components |
Tighten screw connections (with torque) Replace seals/O-rings Replace defective lines/housing Disassembly, testing, correct reassembly |
| Pump doesn't start | No electrical voltage Fuse defective Motor defective Control problem |
Check voltage supply (multimeter) Check/replace fuse Check/replace pump/motor Check machine control system |
| Unusual pump noises | Air suction (cavitation) Bearing wear Foreign bodies in the pump Incorrect viscosity of the oil |
Check oil level, bleed system, check intake line Replace pump Dismantle pump, remove foreign bodies Check oil specification, carry out oil change |
| Oil contamination (discoloration, cloudiness) | Filtering insufficient/defective Ingress of cooling lubricants/water Oil overaged/thermally degraded |
Clean/replace filter, ensure correct filter type Look for and seal leaks, check system separation Change oil, check cause of degradation |
8. Recommended maintenance schedule
A structured maintenance plan is the basis for reliable machine performance. The intervals specified here are recommendations and can be adjusted depending on machine usage and environmental conditions.
| Task | Frequency | Estimated duration | Skill level |
|---|---|---|---|
| Oil level check (visual) | Daily (at machine start) | 5 mins | Machine operator |
| Visual inspection for leaks | Weekly | 15 minutes | Machine operator/maintenance technician |
| Check filter contamination indicator | Weekly | 2 mins | Machine operator/maintenance technician |
| Clean/change filter element | Monthly or every 500 operating hours (depending on display) | 30 - 60 min | Maintenance technician |
| Pump inspection (visual, sound) | Quarterly or every 2000 operating hours | 30 mins | Maintenance technician |
| Checking the lubrication lines and nozzles | Quarterly or every 2000 operating hours | 60 minutes | Maintenance technician |
| Functional test of the system including pressure control | Every six months or every 4000 operating hours | 30 mins | Maintenance technician |
| Complete oil change | Annually or every 8000 operating hours (or when degradation is visible) | 60 - 120 mins | Maintenance technician |
| Electrical testing of the pump and sensors | Every 2 years or 16,000 operating hours | 45 mins | Electrician/maintenance technician |
9. Spare parts reference
The use of high-quality replacement parts is essential for the longevity and functionality of your lubrication system. All components listed below can be found in our UNITEC-D e-catalog.
| Ersatzteilbeschreibung | Typical specification | UNITEC category |
|---|---|---|
| Lubricating oil filter element | Filtration degree 10-25 µm, suitable for OEM filter housings | FILTER |
| lubricating oil pump | Gear pump or piston pump, flow rate (e.g. 0.5 L/min), pressure (e.g. 5 bar), voltage (e.g. 24V DC / 230V AC) | PUMPS & MOTORS |
| Slideway oil | ISO VG 68 or ISO VG 100 according to DIN 51517-3, demulsifying, wear protection (EP additives) | LUBRICANTS |
| O-rings and seals | NBR, FKM or EPDM, specific sizes for filter housings and pump flanges | SEALS |
| Lubrication lines | PA hose (polyamide) or steel pipe, outer diameter (e.g. 4 mm, 6 mm), pressure resistance (e.g. 50 bar) | PIPES & HOSES |
| Pressure gauge | Measuring range 0-10 bar, diameter (e.g. 63 mm), connection (e.g. G 1/4") | MEASURING INSTRUMENTS |
| Lubrication distributor | Progressive distributor or multi-circuit distributor, number of outputs, flow rates per output | DISTRIBUTORS & VALVES |
| Level switch / oil level sensor | Float switch or optical sensor, switching voltage (e.g. 24V DC), connection | SENSORS |
Für eine vollständige Übersicht und Bestellung besuchen Sie bitte: www.unitecd.com/e-catalog/
10. References
- DIN EN ISO 230-1: Acceptance testing of machine tools – Geometric accuracy
- DIN ISO 3498: Lubricants for machine tools
- VDE 0105-100: Operation of electrical systems
- DIN EN 374: Protective gloves against dangerous chemicals and microorganisms
- DIN EN 166: Personal eye protection – requirements
- DIN EN ISO 20345: Personal protective equipment – safety shoes
- Safety data sheets (SDS) of the lubricants used
- Original operating and maintenance instructions from the CNC machine manufacturer
