4-21. Lapping- Continued
The fact that a movement binds or chatters is not always an indication that lapping is necessary.
Disassemble, wash, and thoroughly inspect the parts before lapping. It is possible that inspection will
reveal a small burr which may be easily removed with a file, scraper, or oilstone. A good cleaning, followed
by proper lubrication, may also be enough to smooth out a movement.
Lapping, Using A Surface Plate (fig 4-47). Often it becomes necessary to insure that the mating surface of a
part is flat before assembly into a piece of equipment. An example of this would be in the use of the retainer-
8267736 used in the M145 Telescope Mount. By using a surface plate, the retainer can be lapped to a flat surface
as described below.
Position a surface plate on a suitable work surface.
Selection of abrasive material used in the lapping process will depend upon the
material makeup of the item being lapped.
Select a piece of emery cloth, 8 inches by 11 inches, and cover the back side of the emery cloth with an
adhesive material (two sided tape or other suitable adhesive that will secure emery cloth to the surface
Emery cloth must lay flat against the surface plate with no bends or tears allowed
in the emery cloth
Position the emery cloth (with the adhesive side facing the surface plate) on the center of the surface plate
and press firmly against the emery cloth to secure in place.
Place retainer, with the side to be lapped, on the emery cloth and begin the lapping process. Apply even,
firm pressure on the retainer and move retainer in a figure eight fashion across the emery cloth.
After making two or three passes across the emery cloth, remove the retainer and inspect the side being
lapped. If the retainer is flat, abrasive marks will appear across the entire surface of the retainer.
Intermittent abrasive marks across the surface being lapped indicates the need for further lapping.
If further lapping is necessary, repeat steps (4) and (5) above until a flat surface is obtained as described in
After the lapping process is completed, wash the retainer in Dry Cleaning Solvent to remove all abrasive
Change 6 4-51