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Table 9-5.  Objective, Erector Lenses and Windows
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TM-9-254 Gearcase Transfer M548 M548A1 (
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Decoating Optical Components
TM 9-254 9-7. Decementing (Separating) Optical Components - Continued (2) Place the lens or lenses to be decemented on the hot plate for 1 to 5 minutes.  A slight cracking noise may  be  heard  when  the  thermal  expansion  of  the  lens  breaks  the  cement  bond,  also  the  cement  will become visible between the lens elements. (3) With  a  pair  of  lens  tongs,  carefully  remove  the  lens  from  the  hot  plate  and  place  it  on  a  piece  of cardboard padded with cheesecloth. (4) To separate the lens elements position the lens on its edge.  With a sharp knife apply pressure between the two lens elements. (5) If the lens does not separate, place it back on the hot plate for an additional 1 to 3 minutes, and repeat steps (3) and (4) above. c. Vacuum Oven Method.  This method of decementing lenses is more involved than the hot plate method of decementing and is used primarily to separate large lenses that would fracture when placed on a hot plate.  This method allows the lenses to be heated and cooled slowly in an air free atmosphere thus reducing the possibility of fracturing.  The procedure for decementing with this method is as follows: (1) Place the lenses in vacuum oven on shelves that are lined with fiberglass cloth. (2) Set the oven to a temperature of 350 to 450 degrees Fahrenheit and pump the air out of the oven.  Heat the lenses at this temperature for 24 to 36 hours. NOTE If oven is not equipped with a thermostat graduated in degrees Fahrenheit, place a thermometer inside   the   oven   so   it   can   be   viewed   through   the   front   window   and   adjust   the   temperature accordingly. (3) Turn off the oven and let the lenses cool to room temperature before releasing the vacuum in the oven and removing the lenses. (4) Place the lenses on a piece of cardboard padded with cheesecloth. (5) To separate the lens elements, position them on edge and use a sharp knife to apply pressure between the two elements. (6) If lenses do not separate, repeat steps (1) through (5) above. d. Removing   Cement   from   Lens   Elements.      After   separating   the   lens   elements,   perform   the   following procedures to remove the cement. NOTE This procedure only applies to lenses that do not require recoating. (1) Soak the lens elements in a bath of acetone for approximately 15 minutes. (2) Remove the cement from the lens elements with a piece of cotton.  If all the cement cannot be removed repeat step (1) above. Change 2  9-24

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