Gear Cutting Machine Maintenance Checklist (Pre-Shift, Daily, Weekly, Monthly, Annual)

Daily (including before start of shift)

Check the cutting fluid tank level, leaks and filterCommonBefore start of shiftWhat to checkCoolant tank, tank filter, area around the coolant pumpGuidelineThe level is in the normal range. No leaks from the tank. No chips piled up around the pump. The filter is not cloggedWhen the oil in the tank runs low, discharge pressure drops and oil no longer reaches the cutting point, raising the fire risk (JMTBA). DGUV also requires enough oil volume to keep the cutting point sufficiently submerged throughout machining. JMTBA says machines using oil-based cutting fluid need a level detection or discharge detection function^[1][2]
Check the cutting fluid supply (pump, piping, nozzles)CommonBefore start of shiftWhat to checkCoolant pump, piping, coolant nozzlesGuidelineThe pump has no abnormal vibration, noise, smell or heat. Pressure and flow are normal. No leaks from the piping. The nozzles are not damaged and deliver enough fluid to the cutting edge (cutting point)ProcedureRe-aim the nozzles at the cutting point. DGUV says a large volume at low pressure (2–4 bar) cools better and is less likely to form mistInsufficient supply causes tool wear, breakage and heat, and with oil-based cutting fluid can lead to ignition (JMTBA, DGUV). DGUV lists monitoring of the supply (pressure and flow switches) as a prerequisite^[1][2]
Check the cutting edges and mounting of the tool (hob, pinion cutter, etc.)CommonBefore start of shiftWhat to checkTool cutting edges, flutes, tool mounting sectionGuidelineNo broken edges or abnormal wear. No chips wound around the tool or packed in the flutes. The tool is mounted correctlyA worn or chipped tool overheats at the cutting edge and can throw sparks (JMTBA). Chips packed in the flutes are one cause of hob chipping and abnormal wear (Nidec Machine Tool)^[1][3][4]
When starting from cold, check the tooth thickness of the first part (measurement over pins / span measurement)Hobbing machineBefore start of shiftWhat to checkThe first part in the morning or after a long stopGuidelineThe tooth thickness is within toleranceHeat from the spindle and table changes the center distance and shifts the tooth thickness. Kashifuji says that by replacing the conventional method of circulating coolant to stabilize thermal displacement with a device that compensates the displacement between axes, it can hold the measurement over pins within ±10 µm even from a cold start. Mitsubishi Heavy Industries (now Nidec Machine Tool) also offers models with cooling on the spindle and table axes as a thermal displacement measure. This also serves to check that the machine's own thermal displacement compensation and cooling functions are working properly^[5][6]
Remove chips from inside the machine and the chip discharge pathCommonDailyWhat to checkInside the machining area, on top of covers, chip conveyor, chip containersGuidelineNo chips piled up inside the machine or along the discharge path. The chip conveyor discharges normallyProcedureClean with the machine stopped (see the Safety section: Ordinance on Industrial Safety and Health, Articles 107 and 108). Use a tool such as a brush to clear chips from a running cutting edgeAccumulated chips keep oil from reaching the cutting point and lead to overheating and ignition (JMTBA). DGUV says chips left for days can ignite spontaneously and calls for emptying containers frequently. For a dry-cutting hobbing machine, Mitsubishi Heavy Industries (now Nidec Machine Tool) sealed the machining area with an inner cover to stop chips from scattering and used steeply sloped stainless steel covers to let chips slide smoothly out of the machine^[1][2][7][8]
Clear oil and combustible items from around the machineCommonDailyWhat to checkMachine body and surrounding floor, oil pans and gratings, rag storageGuidelineOil is wiped off the machine body and its surroundings. No oil is pooled in oil pans or gratings. No cardboard, packing material or oil-soaked rags are left near the machineProcedurePut used rags in a lidded container made of non-combustible material. Oil-soaked rags can ignite spontaneously under certain conditions and have caused fires in chip containers and inside machines (DGUV). Do not throw cigarette butts, rags or paper cups into chip containersCommon causes of fire spreading in a machine are oil pans filled to the brim, large-area gratings, oil pools, and paper, cardboard and rags (DGUV)^[2][1]
Check the condition of the automatic fire extinguishing system (on machines that have one)CommonDailyWhat to checkDisplay of the automatic extinguishing system, extinguishing nozzles and piping, fire sensors, extinguishing agent and pressurized gas valvesGuidelineThe power lamp is on. No faults or alarms are shown. The extinguishing agent has not passed its expiry date. Nozzles, piping and sensors are normal. The extinguishing agent and pressurized gas valves are not closedThese are daily inspection items listed by JMTBA. DGUV notes that optical fire sensors do not work when dirty and must be kept clean, for example with an air purge, and that an empty extinguishing agent container leads to re-ignition (DGUV 2024 document). Have the extinguisher maker carry out periodic inspections within the interval it recommends (JMTBA)^[1][2][9]
Check the condition (quality, contamination) of cutting fluid, lubricating oil and hydraulic oilCommonDailyWhat to checkCoolant tank, lubricating oil tank, hydraulic oil tankGuidelineQuality is appropriate. Hydraulic oil and slideway oil have not mixed into the cutting fluid in large amountsJMTBA includes the quality of oils and greases in daily inspection. DGUV says other oils mixed into cutting fluid (hydraulic oil is the largest by volume) degrade machining performance and lead to early tool wear or breakage and machine damage. One approach is to use multi-functional oil compatible with the cutting fluid for lubrication and hydraulics (see the Lubrication section)^[1][2]
Check cables, hoses and the area around the control cabinetCommonDailyWhat to checkMachine cables, hoses, control cabinet / operation panel / terminal boxGuidelineCables are not soiled with oil. No pinching, crushing, kinks or damaged insulation. No cracks or chafing on hoses. No dust or oil inside the cabinet or on terminals. Terminals and connectors are not loose. The cooling unit filter is not dirty. Maintenance outlets are not used permanently or as multi-tapElectrical faults also cause machine fires (daily inspection in JMTBA's fire safety guidelines)^[1](1 source, for reference)

Monthly

Clean or replace the hydraulic unit filter and drain water from the tankCommonWhat to checkHydraulic unit filter, reservoir drainGuidelineIf there is a clogging indicator, follow its reading. If not, clean or replace about once a month. Drain water about once a month, with operation stoppedProcedureWhen changing the filter, always stop the pump and release the residual pressure in the lines and equipment firstMoisture in the air condenses and mixes into the hydraulic oil. Dirty hydraulic oil leads to pump failure and shorter life (Yuken Kogyo operating manual for general-purpose hydraulic units). The interval follows the machine's manual^[10](1 source, for reference)

Other (as needed, first time, etc.)

Clean the mist collector and exhaust ductCommonPeriodicWhat to checkMist collector, exhaust duct, duct access ports and oil drain pipesGuidelineNo oil or dirt has built up inside the duct. The oil drain pipe is not cloggedProcedureThe interval follows the maintenance plan in the equipment's manual. DGUV calls for inspecting local exhaust ventilation at least once a year (German regulation)JMTBA lists the mist collector and exhaust duct under cleaning. DGUV calls for access ports in the duct so deposits can be checked and cleaned regularly, and for including the separator in the extinguishing area where burning chips may be drawn in. Slope the duct gently, with no dips, so oil drains away (DGUV)^[1][2]
Check that the cutting fluid temperature is not risingCommonPeriodicWhat to checkCoolant tank (thermometer or temperature monitor reading, if fitted)GuidelineKept at about room temperatureProcedureUse a large enough oil volume, keep the cutting point well submerged, cool it with baffles, and cool the whole system (DGUV)For every 10℃ rise in cutting fluid temperature, mist generation roughly doubles (DGUV survey)^[2](1 source, for reference)
Test the properties of the hydraulic oilCommonPeriodicWhat to checkHydraulic oil in the hydraulic unitGuidelineYuken Kogyo's guideline for replacing oil in general-purpose hydraulic units: replace with new oil when any of these applies: kinematic viscosity at 40℃ has changed by ±10%, total acid number has changed by 0.5–1.0 mgKOH/g, or water content is 0.2 vol% or moreProcedureTest every 3 months for the first six months, then every 6 months. When replacing, drain all the old oil, clean the tank and refill with the same brand (Yuken Kogyo)Degraded hydraulic oil causes malfunction of hydraulic equipment. On units without a cooler, the oil temperature rises in summer, so switch to a higher-viscosity hydraulic oil if needed. On units with a cooler, if the oil temperature creeps up over several months, suspect fouling of the cooler's heat transfer surfaces (Yuken Kogyo)^[10](1 source, for reference)
Check how the table (workpiece axis) is driven, and if it is a worm drive, include backlash inspection and adjustment in the maintenance planHobbing machinePeriodicWhat to checkTable drive (index worm and worm wheel, anti-backlash device, direct drive motor)GuidelinePer the machine builder's criteria (no figures were found in public material)Play in table rotation directly affects gear accuracy. Each maker uses a backlash-free table drive: Kashifuji uses a device that presses a two-piece split worm together hydraulically to eliminate backlash, Liebherr uses a dual-worm drive or direct drive, and Mitsubishi Heavy Industries (now Nidec Machine Tool) uses direct drive (no gearbox, so less friction loss and part wear). Kashifuji says its anti-backlash device suppresses table rotation vibration and stabilizes accuracy especially for large-diameter workpieces, skiving-hob cutting, and cutting where the hob and workpiece helix directions are opposite. The company advertises maintenance-free rotation accuracy that does not change with age. Some gear shapers use high-precision worm wheels on the cutter head and table (Mitsubishi Heavy Industries)^[5][11][12]
Inspect workholding (arbors, collets) and replace wear partsCommonPeriodicWhat to checkExpansion arbors, collets, segmented collets, disc-spring-type clamping elementsGuidelineClamping force and runout are maintained. Wear parts are within their service limitsGleason says regular maintenance and correct adjustment of clamping devices underpin uptime and quality, and offers periodic on-site inspection or comprehensive maintenance and adjustment at its service centers. Insufficient accuracy or rigidity of the fixture causes lead (helix) errors, and loose clamping causes hob breakage (Nidec Machine Tool). Gleason's collets, segmented collets and clamping springs are designed so worn ones can be replaced without readjustment^[13][14][3]
Have the builder carry out periodic inspection (machine diagnosis)CommonPeriodicWhat to checkWhole machine (axis alignment and runout, mechanical, hydraulic and electrical systems, geometric accuracy and reference positions, level)GuidelinePer the judgment in the inspection reportGleason's inspection program has levels ranging from a simple check (axis alignment, runout, visual check of main systems), to checking mechanical, hydraulic and electrical systems and basic geometric accuracy and reference positions, and further to machine leveling, adjustment of geometric accuracy and reference positions, safety stop checks, machine data backup and wear part replacement. Kashifuji also offers regular machine diagnosis to prevent trouble, and line diagnosis that includes tools and methods. Decide the interval with the builder (public material gives no figure). Gleason's hobbing machine mechanical maintenance course covers the frame, slides, workhead, spindle, ball screws, gearboxes and encoders on all axes, and the hydraulic, pneumatic and coolant systems^[15][16][17]
For an older machine whose accuracy has declined, consider an overhaul (including spindle repair)CommonPeriodicWhat to checkWhole machine, spindleGuidelineWhen the drop in machining accuracy cannot be corrected by adjustmentIn Kashifuji's overhaul, the machine is fully disassembled and cleaned, the wear and accuracy of each unit are inspected, and accuracy is restored by correcting or replacing parts. For spindle repair, Gleason starts with diagnosis and a quotation, replaces parts with genuine ones, and returns the spindle after it passes a test run. Kashifuji also does retrofits that convert old hobbing machines to CNC^[18][19][15]
After mounting the hob on the arbor, measure the runout of the hubs (bosses) at both endsHobbing machineAt setupWhat to checkOuter diameter and end faces of the hob hubs at both ends, hob arborGuidelineRunout is within the tolerance for the hob's accuracy class (the US AGMA hob standard cited by Cluff sets hub runout tolerances by class)ProcedureRemove runout of the arbor itself first, then center the hob by placing a dial indicator on the hubs at both ends. If runout cannot be removed, suspect foreign matter on the center, a bent arbor, clearance between the hob bore and arbor, parallelism of the clamping collars (spacers), or wear of the outboard support bearing (Cluff)The hubs are finished concentric with the hob's tooth form, so removing runout here makes the hob rotate about the correct axis (Liston). Mounting runout ruins hob accuracy and causes tooth profile waviness, profile tilt, pitch error and variation in chamfer amount (Nidec Machine Tool, Cluff). Runout is either eccentricity, where both ends run out in the same direction, or tilt (wobble), where they run out in opposite directions (Liston)^[20][21][3]
Check that the hob shift range, amount and direction suit the workpiece and hobHobbing machineAt setupWhat to checkNC shift settings (start position, end position, shift amount, direction)GuidelineThe shift range is within the effective shift length and the machine's shiftable range. Shifting is always in the direction that brings a fresh cutting edge to the generating sideA shifted position causes unfinished generating or hob damage. Variation in shifting leads to variation in crater wear (Nidec Machine Tool). Calculation of shift amount and effective shift length is covered in the Tool Care section^[22][23](1 source, for reference)
When cutting helical gears, check that the lead of the helical guide matches the cutterGear shaperAt setupWhat to checkHelical guide of the gear shaperGuidelineNearly the same as the lead calculated from the cutter's normal module, number of teeth and helix angle (within the lead error tolerance), and the same helix handThe helical guide guides the cutter's helical motion. If the lead does not match, the lead of the teeth goes wrong (Nidec Machine Tool). Some machines have no helical guide because the helical motion is generated by NC (Nidec Machine Tool's ST series). The lead calculation is covered in the Tool Care section^[24][25](1 source, for reference)
Check that the workpiece is clamped correctly and firmly on the fixture or arborCommonAt setupWhat to checkWorkholding (arbor, collet), clamping deviceGuidelineClamped in the correct position with the specified forceIf the workpiece clamp loosens, the workpiece is turned during machining and the hob chips all at once. With pinion cutters too, insufficient clamping force is a cause of chipping and abnormal wear (Nidec Machine Tool). Skipping setup checks can also lead to collisions or overload, causing heat and fire (JMTBA)^[1][3][4]

📚Sources

Items without a mark are those confirmed by two or more sources from different publishers. Intervals, oil types and values: the specification for each machine takes priority. The text is summarized in Kezuriba's own words.