JQR 131.02 Bore Gage Training (Continued)

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131.02

Use and Care of the Bore Gage
(Continued)

Preparing to use the bore gage

Ensure that the bore gage, standard, and component to be measured are exposed to the same atmospheric conditions for 1 hour before any measurements are taken. Temperature variations between these items can result in erroneous readings.

Use the Bearing Housing Diameter Limits chart to determine the maximum and minimum limits of the bearing size installed.

Clean the bearing housing thoroughly. Use a grease pencil to mark the outside of the housing in three positions, 120 mechanical degrees apart.

Select the standard that corresponds to the bearing size. Wipe the inside of the standard with a lint-free cloth and apply a thin coat of light oil.

Set the standard on a clean flat surface.

Select extension piece appropriate for the standard used.

Insert the extension piece into the gage head.

Wipe the sensitive and centralizing contacts with a lint-free cloth.

Insert the bore gage in the standard, and adjust the extension piece until it approximately fits the standard. Check for scratches on the standard surface which may cause errors in the setting. Adjust the extension piece outward until the indicator on the dial rotates one-half to three-quarters of a revolution.

Gently retighten the locknut;
do NOT force it.

Loosen the bezel clamp. Slowly rock the gage and observe the dial reading.

While holding the gage at the point of maximum travel, set the bezel at zero and lock the bezel clamp.

Place the gage in its box and allow to cool for 4 to 5 minutes. If necessary, recheck and adjust the bezel.

Using the bore gage

Insert the gage in the bearing housing.

For bearing housings less than 1 inch deep, only six readings are required.

Measure the bearing housing at each marked position at three different depths for wide bearings, and at two different depths for narrow bearings. Use the same rocking motion as during calibration.

Record the readings and use the Bearing Housing Diameter Limits chart to determine if they are within limits.

EXAMPLE: A 210 and a 308 standard bearing has an allowable range of 3.5422 to 3.5433. If the standard used to set the bore gage were 3.5428, then the zero mark on the dial equals 3.5428. The allowable readings on the dial when the gage is inserted into the housing would be from -0.0006 to +0.0005.

Readings within limits are acceptable. Remeasure the housing if readings are not within limits.

Recheck gage with standard after each reading to ensure the setting has not changed.

Do NOT hold the gage when not in use, as the heat from the operator's hand can affect readings.

Housings with measurements not within limits will require machining.

Disassemble and clean the gage, extension piece, and standard by wiping with lint-free cloth.

Place the gage in its case. Coat the standard with a light coat of gage block preservative or 2190TEP oil. Stow the gage and standard.

Click on image to enlarge.

Typical Bore Gage

Review Questions
If you can correctly answer the questions below, you have learned the key points in this lesson. Choose the correct answer for each question, then look at your score below the questions. Review the lesson if you miss any questions.