1-7 Accuracy of Gears – Testing and Inspecting

At KHK, the following measuring instruments are used to test and inspect the gear accuracy.

  1. Gear measuring machine……To measure the accuracy of tooth profile, tooth trace (flank line), pitch and runout
  2. 3-D coordinate measuring machine……To measure the pitch accuracy of racks
  3. Composite gear tester……To test composite deviation

3D inspection machinegear measuring machine
Left : 3-D coordinate measuring machine
Right : Gear measuring machine

The measuring equipment used while working on gear production are :

  • Vernier calipers, Micrometer calipers, Cylinder gauge……To measure inside and outside diameters and tooth thickness
  • Runout tester……To measure side face runout, and circumference (radial) runout
  • Hardness testing machine……To measure hardness
  • Micrometer calipers……To find span measurement
  • Gear tooth vernier calipers……To measure tooth thickness of worm
  • Worm gear tester……To measure tooth contact and backlash
  • Bevel gear tester……To measure tooth contact and backlash


vernier caliper

Vernier calipers

micrometer caliper
Micrometer calipers

cylinder gauge
Cylinder gauge

gear tooth vernier caliper
Gear tooth vernier calipers

runout tester
Runout tester

Gear Accuracy in 3D :
gear accuracy in 3D

  1. Radial direction – relevant to tooth proile and tooth depth
  2. Axial direction – relevant to lead error and unevenness
  3. Circumferential direction – relevant to tooth thickness and spacing


In order to test gear accuracy, three-dimensional measurements are necessary, and the following measuring instruments and/or apparatus are to be used properly.
1. Radial direction …. Gear measuring machine, 3-D coordinate measuring machine
2. Axial direction …. Gear measuring machine, 3-D coordinate measuring machine
3. Circumferential direction …. Micrometer calipers, gear tooth vernier calipers, pins (rollers), and ball micrometer calipers
Shown in this figure is the correlation between each individual errors.
There is a strong correlation between each pitch error.
Also, runout error widely influences each individual error.

Correlation between Errors

Correlation between Errors

Figure : Correlation between each individual error (in case of ground gear)
(Deviation and Error)

  • Single pitch deviation
  • Adjacent pitch deviation
  • Base pitch deviation
  • Total profile deviation
  • Total helix deviation
  • Total cumulative pitch deviation
  • Runout error of gear teeth


Related links :
Gear Accuracy – A page of The ABCS of Gears -B
Spur Gears – Main page of spur gears
Accuracy of Gears – A page of Gear Technical Reference