Team Structures Offers Tips to Use an Optical Micrometer
When a skin joint eddy current inspection reveals a crack into underlying crack stopper bands, the next step is to determine the total damage. In order to do this, Team Structures recommends that operators first reference the NDT manual Part 9 section titled “Optical – Inspection of Skin Joints.” An optical depth micrometer is utilized to provide an accurate evaluation of damage along the entire length of the skin joint.
In addition to the manual procedures, the following steps should be used:
1. Clean affected skin joints thoroughly.
2. Place a wide strip of masking tape adjacent to and along the full length of the skin joint. (The tape provides a convenient place to record the measurements taken during inspection.)
3. Mark the tape in one-inch increments along the full length of the joint. (The marks are the inspection points used to inspect the crack stopper band.)
4. For the most consistent results with the optical depth micrometer, the inspection should be conducted by one person without using eyeglasses. (Having more than one person taking the readings may cause errors in the inspection.)
5. Position the optical depth micrometer at the first mark on the side of the joint without the tape. (Accurate readings require solid position ing and no movement during the measuring process.)
a. Adjust the vernier scale and record the setting. (Keep in mind the micrometer does not include a prismatic correction, so the viewed object is upside down.)
b. Without moving the micrometer, clearly focus on the bottom of the crack stopper and record the reading. (A damaged band
c. Subtract the skin thickness and the defined tolerance provided in the NDT manual. (The result is the depth of damage to the crack stopper band.)
6. Repeat the process at each one-inch mark until the full length of the skin joint has been inspected. If further damage is observed at one location, inspect the adjacent areas to find the deepest damage. (The damage may extend several inches past the crack and will need to be addressed for a complete damage evaluation.)
Questions, please contact:
Customer Service Team Structures
Cessna Direct Approach