CalPro Sample Procedure

INDICATORS

Procedure Number: CP21
Subject: Gage Calibration
Revision Number: 01
Date: 01/01/9X

EQUIPMENT:

Indicators

REFERENCES:

Quality System Procedure, Gage Calibration

APPLICATION:

Indicators operate by different systems of displacement amplification, which may consist of gear trains, levers, cams, torsion strips, reeds or a combination of these or other operating systems. The indicator in itself is not a complete measuring instrument but must be used in conjunction with staging or holding devices. Indicators are adaptable to numerous applications including: Comparative measurements of length, bore size, comparison by transferred distance, measurements from fixed reference planes, runout of rotating bodies, etc.

CALIBRATION PROCEDURE:

Vertically operating dial indicators will be checked for accuracy and repeatability using a precision bench micrometer in a horizontal position (a special holding fixture may be constructed for the purpose). The horizontal test type indicator may be checked for accuracy and repeatability using the micrometer height gage or gage block stack-ups. In addition each indicator will be inspected for smoothness of operation, spindle looseness, proper spring tension and backlash in reversing direction. The following steps must be taken in inspecting dial indicators:

1.		Check for sticking. Move the spindle slowly from the rest position to the maximum limit of travel and return by means of hand pressure.
2.		Check for spindle looseness by pushing the spindle back and forth in a direction perpendicular to its axis. Check for rack pin side play by attempting to rotate the spindle, record any deflection.
3.		Note whether the return spring pressure is excessive.
4.		Dial Indicator: Set the indicator up in a precision bench micrometer in a horizontal position so that the spindle is in line with the movable anvil and bears on this anvil. Advance the micrometer head and to different points and note whether the changes in the micrometer head and check different points in the other direction, note whether there is any backlash and record results on the calibration record. Test Indicator: Mount the indicator on a surface gage or height gage and zero the indicator to zero on the micrometer height master. Rotate the micrometer head to different points and note whether the changes in the indicator are the same as shown on the micrometer head. Reverse direction of the micrometer head and check at different points in the opposite direction, note whether there is any backlash and report results on the calibration record.

ACCEPTANCE LIMITS:

Each indicator must meet the requirement of class I or II per MIL -STD-120, Paragraph.: 8.23.1.3, as follows:

a.		The spindle is not to stick at any point across the entire range of the indicator.
b.		Spindle play and rack pin side play must not exceed 0.0002 inch deflection in the dial reading.
c.		There is to be no excessive spring pressure.

Accuracy of calibration will be within plus or minus one unit of graduation at any point covering the entire range of the indicator. The indicator is to repeat to zero at rest. On indicators graduated to 0.0001 inch or less the acceptable tolerance for this requirement is one graduation. On indicators where the graduations are 0.0005 inch or more the tolerance is 0.0002 inch.

CALIBRATION FREQUENCY:

Three (3) months.

SPECIAL REQUIREMENTS:

None.