Gear Cutting Machine Troubleshooting Quick Reference (Spindle Heat, Abnormal Noise, Chatter, Dimensional Drift)

Tooth profile is wavy (undulating profile)Hobbing machine

Likely cause	What to check	Action
Hob hub has runout (mounting runout)	Runout of the hub outer diameter and end faces	Re-center using the arbor and hubs. If runout cannot be removed, check the arbor, collars and center^[1][2][3]
Flute indexing from sharpening (spacing of cutting faces) is uneven	Single and cumulative flute indexing error	Regrind all flutes by the same amount. Check runout during sharpening and wear of the indexing plate^[1][3][4]
Hob bore is too large (clearance to the arbor)	Hob bore diameter and arbor diameter	Correct the fit between bore and arbor. Replace a worn arbor^[1][2]
Poor hob lead accuracy or tooth profile, poor mounting accuracy on the arbor	Hob inspection report, inspection after sharpening	Regrind or recondition the hob, or replace it^[1](1 source, for reference)

Tooth profile is tilted (pressure angle is off, tooth tip too thin/thick)Hobbing machine

Likely cause	What to check	Action
Error in the sharpening rake angle, poor radiality (convex or concave rake face)	Measure radiality, check the rake angle and rake offset marked on the hob end face	Resharpen to the designed rake. Grind helical flutes with the conical side of a dish wheel^[5][1][3][4]
Hob hub runout, poor hob tooth profile	Hub runout, hob inspection report	Correct the mounting. Recondition or replace the hob^[1](1 source, for reference)
(Apparent defect) Workpiece runout when measuring the gear	Mounting of the workpiece on the measuring machine	Correct the mounting and measure again^[1](1 source, for reference)

Large pitch error / cumulative pitch errorHobbing machine

Likely cause	What to check	Action
Hob hub runout, poor mounting accuracy on the arbor	Hub runout	Re-center^[1][2]
Poor flute indexing from sharpening, poor hob lead accuracy	Inspection after sharpening	Resharpen^[1](1 source, for reference)
(Apparent defect) Workpiece runout during measurement	Mounting on the measuring machine	Measure again^[1](1 source, for reference)

Large lead (helix) errorHobbing machine

Likely cause	What to check	Action
Poor hobbing machine accuracy	Geometric accuracy (JIS B 6216, ISO 6545), the builder's periodic inspection	Adjust axis alignment and geometric accuracy^[1][6]
Poor hob lead accuracy	Hob inspection report	Recondition or replace the hob^[1](1 source, for reference)
Poor accuracy or insufficient rigidity of the workholding fixture, or insufficient rigidity of the workpiece (Nidec Machine Tool lists these as causes of lead error in gear shaping)	Fixture runout and seating surfaces, clamping	Inspect and adjust the fixture, and replace worn parts^[7][8]
(Apparent defect) Workpiece runout during measurement	Mounting on the measuring machine	Measure again^[1](1 source, for reference)

Tooth thickness (measurement over pins), outside diameter and root diameter are off or varyHobbing machine

Likely cause	What to check	Action
Wrong hob setting angle, or setting angle changed as a measure against flank scratches	Setting angle	Return to the correct setting angle, or allow for the loss in tooth thickness (one example: 1° of setting angle reduces tooth thickness by about 32 µm)^[1][9][10](1 source, for reference)
Poor infeed dimension for gear cutting, poor hob tooth thickness or tooth depth, poor radiality	Infeed setting, hob inspection report	Correct the infeed. Resharpen the hob^[1](1 source, for reference)
Dimensions change as the hob is shifted (taper from error in the sharpening flute lead, effect of runout with multi-shift)	Tooth thickness at each shift position	Resharpen to the correct flute lead. Review the shifting method (one-pitch shifting is less affected by runout)^[2][3][11]
Thermal displacement from heat in the spindle and table (starting from cold)	Time since start of shift and a record of tooth thickness	Check the thermal displacement compensation and cooling functions. Define a first-part measurement^[12][13]

Chamfer amount is too large or too small, or differs left to right or tooth to toothHobbing machine

Likely cause	What to check	Action
Poor hob chamfer height, poor workpiece outside diameter, poor infeed dimension, poor radiality	Hob and workpiece dimensions, infeed amount	Correct the dimension at fault^[1](1 source, for reference)
Wrong or changed hob setting angle (holding back the cut to make up tooth thickness reduces the tooth tip chamfer)	Setting angle	Return to the correct setting angle^[1][9](1 source, for reference)
(Differs tooth to tooth) hub runout; (differs left/right or tooth to tooth) poor hob lead accuracy	Hub runout, hob inspection	Re-center. Recondition the hob^[1](1 source, for reference)

Scratches or tearing on tooth flanks in dry hobbingHobbing machine

Check whether the scratches are at the same position on all teeth (scratched by chips during generating) or whether scratched and unscratched teeth are mixed (a detached chip is caught in the cut; welding may be visible) (Nidec Machine Tool)^[10]

Likely cause	What to check	Action
Tooth flanks scratched by chips during generating (same position on every tooth)	Scratch position	Change the setting angle by about 15′ to 1° in the direction that increases the entry angle of the hob cutting edge on the scratched flank side (note that tooth thickness decreases)^[10][9](1 source, for reference)
A detached chip is caught at the cutting point (scratched and unscratched teeth are mixed)	Scratch distribution, welded chips	Change the setting angle in the direction that decreases the entry angle, and bring an air nozzle close to the cutting point to keep chips away^[10](1 source, for reference)
(Tearing on the tooth profile surface or outer diameter) Interference at the hob's relief run-out section	Hob design	Consult the tool maker^[1](1 source, for reference)

Hob chips (breaks)Hobbing machine

Likely cause	What to check	Action
Grinding cracks during sharpening or profile grinding (chipping that starts from a crack)	Whether the fracture surface shows a crack origin	Sharpen without causing grinding burn (touch lightly on a high flute before feeding, dress, spark out)^[1][4]
Plunging at rapid traverse	Program, setup	Check the program and tool position offsets before actual cutting^[1][14]
Loose workpiece clamp lets the workpiece be turned during machining	Clamping force, workholding	Inspect the clamping and replace worn parts^[1](1 source, for reference)
Chips pack the flutes because of insufficient cutting fluid flow or poor delivery	Flow rate, nozzle direction	Ensure the supply volume and aim the nozzles at the cutting point^[1][14]
Cut a hard object such as a fixture, poor hob base material (too hard or brittle), cracking near the crater from cutting heat	Presence of interference, shape of the chipping	Eliminate the interference. Ask the tool maker to investigate^[1](1 source, for reference)

Hob wears quickly or abnormallyHobbing machine

Likely cause	What to check	Action
Variation in hob shifting (crater wear varies)	Shift settings, number of parts between shifts	Reset the shift range, amount and direction^[1][11](1 source, for reference)
Sharpening is done too late (cutting edge collapses from crater wear)	Amount of flank wear and crater wear	Sharpen at about 0.1–0.2 mm flank wear (coated hobs)^[5](1 source, for reference)
Coating peeling (poor treatment)	Peeling in the worn area	Ask the tool maker to investigate^[1](1 source, for reference)
Wear while chips are packed in the flutes because the flute volume is small or cutting fluid is insufficient	Chips in the flutes	Ensure the cutting fluid supply. Review the tool design^[1][14]
(Uniform wear) Poor hardness, material or heat treatment of the hob base material; (wear at the tip radius blend) the tip radius blend is angular	Wear pattern	Consult the tool maker^[1](1 source, for reference)

Poor tooth profile, pitch or lead in gear shaping, or a step appears on one toothGear shaper

Likely cause	What to check	Action
Poor cutter tooth profile, poor rake angle or sharpening angle	Cutter inspection and sharpening records	Resharpen while keeping the rake angle (normally 5°) and sharpening angle^[7][15](1 source, for reference)
(Step on one tooth, tooth space runout) Poor tooth space runout or cumulative pitch on the cutter, poor mounting accuracy of cutter and workpiece	Mounting runout of the cutter and workpiece	Correct the mounting. Recondition or replace the cutter^[7](1 source, for reference)
Poor gear shaper accuracy (pitch, profile, lead)	Builder's accuracy inspection	Request adjustment or repair^[7][16](1 source, for reference)
(Poor lead) Insufficient rigidity or poor accuracy of workpiece or mounting fixture, helical guide lead does not match the cutter	Fixture, calculation of the helical guide lead	Repair the fixture. Replace with a matching helical guide^[7][17](1 source, for reference)

Pinion cutter chips or wears abnormally, or tooth flanks tearGear shaper

Likely cause	What to check	Action
Unsuitable cutting conditions (cutting speed or feed too high), plunging at rapid traverse	Conditions table, program	Review the conditions^[7](1 source, for reference)
Insufficient clamping force on cutter or workpiece, workpiece hardness too high	Clamping, workpiece hardness	Correct the clamping^[7](1 source, for reference)
Interference from relieving (clearance on the return stroke), the cutter hits the shoulder or chips pack in between	Relief amount and stroke position	Correct the relief and stroke settings^[7](1 source, for reference)
Excessive cut when resharpening, sharpening done too late (flank wear and welding progress)	Sharpening records, wear width	Sharpen at about 0.2–0.3 mm wear width, and do not grind deeply in one pass^[7][15](1 source, for reference)
(Tearing) Sticky workpiece material, unsuitable or degraded cutting fluid, overly deep infeed leaving root stock or a step on a helical pinion	Condition of the cutting fluid, shape of the cutter	Review or change the cutting fluid. Review the cutter specification with the tool maker^[7](1 source, for reference)

In shaving, the tooth profile does not come out or breaks down quickly, or the cutter life is short or it chipsShaving machine

Likely cause	What to check	Action
(Discrepancy in judgment) Different measuring machine, different tooth measured, different control point on the tooth profile	Measurement conditions	Compare using the same measuring machine, same tooth and same control point^[18](1 source, for reference)
(Difference between trial cutting and production) Different machine, different conditions, different accuracy of the preceding process (rough cutting)	Accuracy of the gear from the previous process	Make the accuracy of the preceding process consistent^[18](1 source, for reference)
(Workpiece tooth profile breaks down quickly) Low cutter hardness, complex cutter tooth profile, shaving stock too large, high workpiece hardness	Stock allowance, cutter specification	Review the stock allowance. Review the cutter specification with the tool maker^[18](1 source, for reference)
(Few resharpenings possible) Serrations are shallow (differences left/right, tip vs. root, around the circumference, or shallow overall)	Regrinding records and diagrams	Ask the tool maker for regrinding and records^[18][19]
(Chipping during machining) Interference with a shoulder gear, cutting a workpiece of a different specification, too many parts machined (wear), insufficient strength at the cutter tooth root, unsuitable serration arrangement	Interference, workpiece specification	Eliminate the interference. Set the tool life^[18](1 source, for reference)

Oil-based cutting fluid ignites, or a fire starts inside the machineCommon

Most fires occur during long unattended operation using oil-based cutting fluid. The ignition source is mostly glowing chips, grinding sparks or an overheated tool, and hot surfaces of 800℃ or more are an especially effective ignition source (DGUV)^[14][20]

Likely cause	What to check	Action
The cutting edge overheats and ignites from tool breakage or abnormal wear	Tool condition, load	Manage tool life and stop machining with an abnormal load detection function^[14][20]
Cutting fluid is not reaching the cutting point sufficiently (low level, low discharge pressure, nozzle direction)	Level, pressure, flow, nozzles	Refill and correct the nozzles. Add level and discharge detection^[14][20]
Chips pile up in the machine and overheat, or spontaneous ignition in the chip container	Chips in the machine and containers	Clean frequently and empty the containers^[14][20]
Overload from overly severe cutting conditions, a tool path that interferes, or setup mistakes	Conditions, program, setup	Use conditions suited to the workpiece material and tool, and check the program before actual cutting^[14](1 source, for reference)
(Re-ignition after extinguishing) Opened the door or restarted before the machine had cooled, extinguishing agent container empty	Procedure after extinguishing, amount of extinguishing agent	Do not open the door until it has cooled, and do not rush to restart. Monitor the amount of extinguishing agent^[21][20](1 source, for reference)

Heavy oil mist, or mist leaking outside the machineCommon

Likely cause	What to check	Action
Cutting fluid temperature is rising (mist roughly doubles for every 10℃ rise)	Oil temperature	Use enough oil volume and keep it near room temperature with baffles or cooling^[20](1 source, for reference)
Nozzle pressure, shape and direction are wrong (high pressure, high cutting speed or the way spatter hits turns the fluid to mist)	Nozzle	Flow a large volume at low pressure and aim it at the cutting point^[20](1 source, for reference)
Mist collector or duct is dirty or clogged	Mist collector, duct	Clean it. Replace filters according to the maintenance plan^[14][20]
Fluid that evaporates or forms mist easily	Fluid properties (flash point, evaporation loss)	Choose a low-emission fluid (low-evaporation base oil, with a mist suppressant) together with the fluid maker. Mist suppressants lose effectiveness with use and can clog fine filters^[20][22]

Play in the table, or rotation is not smooth (vibration)Hobbing machine

Likely cause	What to check	Action
Backlash in the table drive worm	Builder's inspection (motion accuracy test)	Ask the builder to inspect and adjust the anti-backlash device and replace parts^[12][23]
Hydraulic pressure is not correctly applied to the hydraulic anti-backlash device	Hydraulic oil level and pressure	Inspect the hydraulic unit^[12][24]

📚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.