Problems on this page:
Tooth profile out of tolerance
Hits OEE: Quality
Symptoms: Gear inspection shows profile or involute errors on the cut teeth.
Hob worn or sharpened incorrectly
Check the hob against its sharpening record and have it reground or replaced.
Hob mounted with run-out
Clean the arbor and hob bore, remount the hob and check the run-out with a dial indicator.
Hob shift not used or set wrong
Use hob shifting so wear spreads along the hob, and check the shift settings.
Blank not clamped true
Check the workholding and the blank faces for burrs and dirt.
Prevention: Gear inspection on the first part after each hob change and on a fixed sample.
Lead or helix angle error
Hits OEE: Quality
Symptoms: The tooth lead is off, so the gear contacts at one end of the tooth.
Differential or helix setting wrong
Check the helix angle and the differential settings in the program.
Workpiece axis out of alignment
Check the tailstock and work arbor alignment.
Machine axes worn
Have the axes checked during planned maintenance.
Blank bore and face not square
Check the blank squareness from the turning operation.
Prevention: Lead measured on the first part of each batch.
Poor surface finish on the teeth
Hits OEE: Quality
Symptoms: Tooth flanks show feed marks, tearing or a rough finish.
Hob worn
Regrind or replace the hob.
Feed rate too high for the finish needed
Lower the axial feed for the finishing cut.
Coolant not reaching the cut
Check the coolant nozzles, flow and concentration.
Chips recut in the tooth space
Improve chip flushing at the cut.
Prevention: Finish checked on samples against the drawing.
Hob wearing quickly
Hits OEE: Availability
Symptoms: Hobs need regrinding much sooner than their usual life.
Cutting speed too high for the material
Check speeds against the tool maker data for the material.
Material harder than specified
Check blank hardness from the heat treat or supplier.
Hob shift range too small
Use the full shift range of the hob.
Coolant concentration low
Check and correct the coolant concentration.
Prevention: Hob life recorded per material and batch.
Pitch or spacing errors
Hits OEE: Quality
Symptoms: Inspection shows uneven tooth spacing around the gear.
Index or table drive backlash
Have the table drive checked for backlash.
Workpiece slipping in the fixture
Check clamping force and fixture surfaces.
Temperature change during the cut
Let the machine warm up before precision work.
Program error in the tooth count
Check the tooth count and gear data in the program.
Prevention: Spacing checked on the first part and after any table repair.
Burrs on the tooth ends
Hits OEE: Quality
Symptoms: Heavy burrs form where the hob leaves the tooth and need extra handwork.
Hob cutting edges dull
Send the hob for regrinding before the burr grows; a dull edge pushes metal out of the tooth end.
Climb or conventional direction not suited to the part
Check the cutting direction set in the program against the hob maker advice.
No deburring step after hobbing
Add a chamfering or deburring operation where the drawing calls for clean tooth ends.
Thin parts unsupported at the exit side
Support thin gears at the exit face so they do not flex as the hob leaves.
Prevention: Burr checks at the first part of each batch.
Chatter during cutting
Hits OEE: Quality
Symptoms: The machine chatters during the cut and leaves wave marks on the tooth flanks.
Workholding not rigid enough
Shorten overhangs, and check the fixture and arbor for wear and play.
Hob arbor outboard support worn
Check the outboard support bearing and replace it if it has play.
Feed or depth too aggressive for the setup
Reduce the feed or split the cut into two passes and compare the finish.
Machine level or foundation bolts loose
Check the machine level and tighten the foundation bolts.
Prevention: Chatter noted against the part number and settings so repeat cases stand out.
Long changeovers between gears
Hits OEE: Performance
Symptoms: Changing to another gear takes long and the first parts need adjustment.
Hobs and fixtures not prepared in advance
Prepare the next hob and fixture while the current batch runs.
Hob mounting and run-out check slow
Use a presetting stand and record the run-out.
Programs not stored per gear
Store a proven program for each gear.
First part waits for the inspection room
Plan inspection capacity for first parts.
Prevention: Changeover time recorded per gear family.
Coolant problems in the cut
Hits OEE: Quality
Symptoms: Smoke, burn marks or a poor finish appear on the teeth during cutting.
Coolant level or pump flow low
Check the tank level and the pump output, and look for leaks in the lines.
Nozzles blocked or pointing away from the cut
Clean the nozzles and aim them where the hob enters the blank.
Concentration wrong
Measure the concentration with a refractometer and correct it as the supplier specifies.
Chip filters blocked
Clean the chip filters and check that the conveyor is clearing chips.
Prevention: Coolant level and concentration checked daily.
Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.
Related equipment guides: CNC machine · lathe · broaching machine · gearbox · deburring machine
Stop the same fault coming back
Recurring gear hobbing machine stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.
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Related tools: full troubleshooting directory · OEE calculator · downtime cost · MTBF / MTTR · glossary
Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover