Radius Gage Calibration


The purpose of this procedure is to provide general instructions for the calibration of radius gages.


The radius gages is considered an in an inherently stable device and will not require recalibration unless a special request is made by the user.


The use of radius gages is a fast and easy method of checking concave or convex radii in machining, layout, pattern making, etc. for tool and die makers, machinists, layout men and other mechanics. Calibration is performed by comparing the radius gage to a radius chart on an optical comparator.

Preliminary Instructions and Notes

  1. Read this entire procedure before beginning the calibration.
  2. Calibration shall be performed in an environment that conforms to Manufacturer Specifications.
  3. The radius gage will hereafter be referred to as the Instrument Under Test (IUT).
  4. Verify that the IUT is clean.
  5. Visually examine the IUT for any condition that could cause errors in the calibration.
  6. If any of the requirements cannot be met, refer to the applicable manufacturer manual.
  7. If a malfunction occurs or a defect is observed while calibration is in progress, the calibration shall be discontinued and necessary corrective action taken; if corrective action affects a measurement function previously calibrated, the function shall be recalibrated before the remainder of the procedure implemented.

Reference Material

Applicable Manufacturers Manual or Brochures.


The specifications of the IUT are determined by the applicable manufacturer's documentation. If the manufacturer's documentation is not available, then the specifications identified in this procedure are used.

Dimensions of these instruments are in fractions or decimal inches or in millimeters. This procedure will use decimal inches for all dimensional measurement but will be applicable to all equivalent dimensions.


Range Assigned Accuracy
0.016 through 0.125 Inch +/- 0.002 Inch
0.141 through 0.234 Inch +/- 0.003 Inch
0.500 and larger +/- 0.004

Equipment Required

The Standards listed below should be selected on the basis of their higher accuracy level when compared to the IUT. Equivalent Standards must be equal to or better than the Minimum-Use-Specification.

Minimum-Use-Specifications for Standards listed are 1/4 the accuracy required by the IUT.

Required Equipment

Standards Used Minimum-Use-Specifications
Optical Comparator Accuracy: +/- 0.0005 Inch
W/Radius Charts With Calibration Radius Charts

Detailed Procedure

  1. Select appropriate radius chart and mount on optical comparator.
  2. Mount the IUT on the worktable of comparator and align with the best-fit radius.
  3. Repeat step 2 for each concave and convex radius on IUT. If IUT is one in a set of similar instruments, each IUT must be checked.

Reason for Reissue

Revision A - First Release