(3)  
Hand polishing or buffing operations should be done with circular motion of hand and cover as large a portion of window as possible. Start at pane center and work outwards to edges. It is preferable to use a clean cloth for each operation in the procedure. Superficial scratches can be removed by applying polish to a wet clean cloth and rubbing window, but minor scratches may require rubbing first with cloth and fine buffing compound such as Learock No. 888 and finishing with one of the listed polishes.

(4)  
Machine polishing and buffing are preferred when equipment and a qualified operator are available. The contact pressure and wheel speed must be regulated to prevent overheating the surface. 

CAUTION:  TO AVOID OVERHEATING WINDOW, KEEP BUFFING WHEEL IN CONSTANT MOTION OVER WINDOW SO THAT WINDOW SURFACE TEMPERATURE DOES NOT EXCEED 125 TO 130°F. AT THIS TEMPERATURE, WINDOW WILL NOT FEEL HOT WHEN TOUCHED BY BACK OF HAND WITHIN 2 SECONDS OF REMOVING PANE FROM BUFFING WHEEL.

(5)  
Minor or superficial scratches can be removed by using machine polishing or buffing with Learock No. 888 buffing compound. If required, preliminary buffing may be done with a stitched muslin wheel and a buffing compound such as Learock S-30 at a wheel surface speed of 3200 feet per minute. The final high gloss polishing is then done with Learock 888 compound on a loose open unstitched muslin wheel with spacers or a loosely stitched flannel wheel at a surface speed of 4200 feet per minute. (To make spacers, remove all the muslin disks and reduce half of them to 1/2 the original diameter. Reassemble wheel, alternating large disks with small ones. This type of wheel reduces heating due to friction.) Sometimes an unsatisfactory condition can be detected at the edge of the buffed area. If window is held at the correct angle to the light, a very slight clouded margin can be seen. One cause of this condition is insufficient wheel speed. This problem can be eliminated by increasing wheel speed or by buffing entire surface of window.

(6)  
After window has been polished, it should be carefully measured to ensure that it complies with minimum thickness requirements and then waxed. One of the approved waxes should be applied to window and lightly polished with a flannel cloth. Finally, window faces should be brushed or sprayed with Spraylat or masked with an approved tape for storage.

B.  Hand sanding should be used to remove buildup material on major scratches. Use of a buffing wheel with an abrasive compound on this type of scratch may result in excessive optical distortion. A vibrator with sandpaper is not recommended as excessive material may be removed from window.
(1)  
Before hand sanding damaged area, window should be cleaned and masked as described in par. 4.A.(1) and (2).

(2)  
Start sanding with wet-and-dry No. 400-A sandpaper which has been soaked in water for a few minutes. Wrap paper around a rubber block having a Shore Type "A" durometer hardness of 35 or a wooden block wrapped with several layers of flannel. By sanding an area approximately 4 inches in diameter optical distortion can be minimized. Surface should be rubbed across the scratch at a 45- degree angle using light hand pressure with frequent applications of water. Change sandpaper as required. The affected area should  be sanded with No. 400-A sandpaper until scratch buildup material is removed. The sanding abrasions are then reduced by repeating sanding with No. 600-A wet-and-dry sandpaper which has been soaked in water.

(3)  
After sanding, scratches should be in the minor category and sanded area takes on a frosted appearance. Apply Learock S-30, or its equivalent, to a buffing wheel and buff affected area as detailed in par. 4.A.(2) until frosted finish is removed. Optical transparency occurs at the time all frosted finish is removed. The use of Learock S-30 should cease at this point as overusage of S-30 results in optical distortation.

(4)  
Apply Learock 888 buffing compound to a clean buffing wheel and polish the window surface to a high gloss, as described in par.  4.A.(4).

(5)  
Following repair, check that window thickness complies with minimum thickness requirement, lightly polish with one of the approved waxes and protect faces with Spraylat or an approved tape.

501 
56-31-0 Page 804  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 01/76 

501 
May 01/76  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  56-31-0 Page 805 

VIEWERS AND OBSERVATION WINDOWS - DESCRIPTION AND OPERATION
　
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