The gear tooth Vernier caliper is a highly specialized instrument designed specifically for measuring the tooth thickness of gears — one of the most critical dimensions in gear manufacturing, because tooth thickness directly affects the backlash, load distribution, and noise characteristics of a gear mesh. Standard Vernier calipers cannot make this measurement accurately because gear teeth have an involute curved profile, which means the chord thickness of the tooth at the pitch circle must be measured at a specific, precise depth (the chordal addendum) below the tooth tip.
The gear tooth Vernier caliper solves this problem with two independent Vernier scales and adjustments working in two perpendicular directions simultaneously. One scale (vertical) sets the depth of measurement precisely to the chordal addendum for the specific gear module and number of teeth being measured. The other scale (horizontal) then measures the chordal tooth thickness at that exact depth. Both dimensions are calculated from the gear’s specifications (module and number of teeth) and must be set and read independently on the instrument.
This instrument requires the operator to first calculate the correct chordal addendum from gear geometry tables or formulas, set that dimension on the vertical scale, then take the horizontal chord measurement. It’s used in gear manufacturing shops, gear repair facilities, and quality control departments wherever precision gears are made or inspected.
It’s applicable to spur gears, helical gears (with appropriate corrections for the helix angle), and bevel gears. While coordinate measuring machines (CMMs) and gear measurement centers have taken over gear inspection in high-volume production environments, the gear tooth Vernier caliper remains an important handheld tool for setup verification, repair work, and situations where CMM access isn’t practical.