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Gear Cutting Machine Lubrication

Where to lubricate, oil types and viscosity (ISO VG), and replacement guidelines. Intervals, oil types and values: the machine builder's and tool maker's specifications and the operating manual of your own machine take priority. The values here are examples found in public material. Storage and handling of oil-based cutting fluids must follow the Fire Service Act (Japan) and municipal fire prevention ordinances, under the guidance of the local fire department

⛽Lubrication points and oils

Location	Machine	Oil (example)	Interval guideline
Slideways (guide surfaces of the column, saddle, etc.)	Hobbing machine	As specified by the machine builder (slideway oil or grease)Kashifuji's hobbing machines use a low-viscosity grease lubrication system on the slideways, and by lengthening the lubrication interval compared with oil lubrication they reduce lubricant consumption. The company scrapes the slideways, and says the shallow hollows left by scraping act as oil pockets that improve lubrication of the sliding motion. A standard for machine tool lubrication systems is JIS B 6016-2 (adopted with modification from ISO 5170). On machines using oil-based cutting fluid, one approach is to choose a compatible oil on the assumption that slideway oil will mix into the cutting fluid (DGUV)	Many machines have automatic lubrication. Quantity and interval follow the machine's manual^[1][2][3]
Table (workpiece axis) bearings and drive	Hobbing machine	Oil specified by the machine builder (no oil type was found in public material)Table construction differs greatly by machine. Liebherr's large hobbing machines use hydrostatic radial and thrust bearings on the table spindle, drive the table with a dual-worm drive or direct drive, and water-cool the drive motor. Kashifuji uses a hydraulic two-piece split worm anti-backlash device on the table axis. Mitsubishi Heavy Industries (now Nidec Machine Tool) offers models with direct drive	Depends on the machine^[4][1][5]
Hydraulic unit (workpiece clamping, table anti-backlash device, etc.)	Common	Hydraulic oil specified by the machine builderOn Liebherr's hobbing machines, a hydraulic clamping cylinder sits in the large bore of the table and moves the workholding	Oil level and temperature daily. Drain water about once a month. Test properties every 3 months for the first six months, then every 6 months (guideline for Yuken Kogyo general-purpose hydraulic units)^[6][4][1]

🛢Oil types and how to choose

Straight cutting oil (oil-based cutting fluid)Choose the one with the highest flash point and lowest evaporation loss within the viscosity the machining requires (DGUV): Provides lubrication and chip removal in hobbing, gear shaping and similar work. It is a combustible oil, so fire countermeasures are required. Under the Fire Service Act, the class depends on flash point: 70℃ to under 200℃ is Class 3 Petroleums (designated quantity 2,000 L for water-insoluble), 200℃ to under 250℃ is Class 4 Petroleums (6,000 L), and liquids of 250℃ or higher are not hazardous materials but designated combustibles, combustible liquids (2 m³ or more). ENEOS's high-flash-point cutting oil (Reliacut AE) is classified as Class 4 Petroleums. The higher the viscosity, the harder it is to filter and the lower the flow rate (DGUV)^[7][8][9][3]
Water-soluble cutting fluid— (used diluted): Reduces fire risk. Also used for high-speed gear cutting. JMTBA recommends using water-soluble cutting fluid wherever possible to lower the chance of fire and prevent it spreading. However, with easily ignited metals such as magnesium, water-soluble fluid releases hydrogen and risks an explosive fire, so use a dedicated or oil-based fluid. Nachi-Fujikoshi offers coated hobs suited to high-speed hobbing above 300 m/min with water-soluble cutting fluid. Kashifuji says high-speed machining with water-soluble fluid requires separate water-soluble-specific specifications on the machine^[10][11][1]
Dry cutting (machining without cutting fluid)—: Eliminates the cost of cutting fluid and the sources of fire and mist. Put to practical use on hobbing machines and gear shapers. Mitsubishi Heavy Industries (now Nidec Machine Tool) completed a gear machining system using no cutting fluid at all in 1997 and extended dry cutting to hobbing machines and gear shapers. Kashifuji offers hobbing machines capable of ultra-high-speed dry machining at a cutting speed of 300 m/min. Dry cutting tends to cause tooth flank scratches from chips being caught in the cut, and one countermeasure is to bring an air nozzle close to the cutting point to keep chips away (Nidec Machine Tool)^{[12][13][1][14]}
Multi-functional oil (lubricating and hydraulic oil compatible with cutting fluid)Decide in consultation with the machine builder and the oil maker: Matches hydraulic oil, slideway oil, gear oil and spindle oil into a combination compatible with the cutting fluid, so that the cutting fluid's performance is less likely to drop even if they leak and mix. DGUV says this makes the cutting fluid process more reliable, extends the life of the fluid and reduces maintenance effort^[3](1 source, for reference)
Hydraulic oilAs specified by the machine builder: Operates workpiece clamping, the table anti-backlash device, hydrostatic bearings and so on. Guideline for replacing petroleum-based hydraulic oil: kinematic viscosity at 40℃ changed by ±10%, total acid number changed by 0.5–1.0 mgKOH/g, water content 0.2 vol% or more (Yuken Kogyo general-purpose hydraulic units)^[6](1 source, for reference)

📚Sources

Items without a mark are those on which two or more materials from different publishers agree. Values and intervals are governed by each machine's specifications. The text is summarized in Kezuriba's own words.