Gear defect – tooth surface defect


Main cause

1) Uneven material of gear blank

2) Improper heat treatment of gear blank

3) Chip accretion due to unreasonable selection of cutting parameters

4) Low efficiency of cutting fluid

5) The hob is blunt and not sharp


1) Control the material quality of gear blank

2) Proper selection of heat treatment method, especially the hardness after quenching and tempering treatment, and normalizing treatment is recommended

3) Correct selection of cutting parameters to avoid chip accretion

4) Select cutting fluid correctly, especially pay attention to its lubrication performance

5) Replace with a new knife

2.Gnaw teeth

Main cause

Due to the sudden change of the position between hob and gear blank:

1) The triangular guide rail of column is too loose, resulting in sudden change of hob feed, and the triangular guide rail of column is too tight, resulting in crawling

2) Large meshing clearance of cutter head helical gear

3) Unstable oil pressure


Find and eliminate some unexpected factors:

1) Adjust the triangular guide rail of column: it is required to be tight and loose properly

2) If the tool holder is worn due to long service life, it should be replaced

3) Maintain the machine tool reasonably, especially clean, keep the oil way smooth: keep the oil pressure stable

3.Vibrating marks

Main cause

Due to vibration:

1) The gap of a transmission link in the machine tool is large

2) The clamping rigidity of workpiece and hob is not enough

3) Too large cutting amount

4) Large clearance after rear bracket installation


Find and eliminate vibration sources:

1) Overhaul the machine tools with long service time and serious wear

2) Increase the clamping rigidity of hob, for example, reduce the distance between supports; the hob with handle shall select large shaft diameter as much as possible. Improve the clamping rigidity of the workpiece: for example, increase the supporting end face as much as possible, and the supporting end face (including the workpiece) is only allowed to be concave; shorten the distance between the upper and lower thimbles

3) Correct selection of cutting parameters

4) Install the rear bracket correctly

4.Fish scales

Main cause

The heat treatment of gear blank is improper, especially in the processing of steel parts after quenching and tempering


1) Control the hardness of quenching and tempering treatment as appropriate

2) It is suggested to adopt normalizing treatment as the pre heat treatment of gear blank