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Removing the Bobbin
ROTARY SEWING MACHINES

Aircrew Survival Equipmentman 2 - Aviation theories and other practices
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turn the screw clockwise. To decrease the tension, turn the screw counterclockwise. The tension on the machine and bobbin threads should be checked by test-running a row of stitches on scrap material. The lockstitch should lock in the center of the material, as described for the 31-15. When sewing webbings with the 7-33 sewing machine, the specifications for webbing sewing should be checked to determine at what ply of the webbing the stitch should lock. Regulating the Length of Stitch The procedure for regulating the stitch on the 7-33 ‘sewing machine 31-15. Regulating the Pressure on the Material is the same as for the The pressure on the material is regulated by means of the hexagon head screw (1). (See figure 9-22.) Loosen the hexagon head locknut (2) and turn the adjusting screw clockwise to increase the pressure, or counterclockwise to decrease the pressure on the spring (3). When the desired pressure has been obtained, hold the adjusting screw with a wrench to keep it from turning while 239.279 Figure 9-22.—Regulating the pressure on the material. 9-17 the locknut is being tightened against the bracket (4). The pressure should be just heavy enough to enable the feed dog to move the work along evenly, and to prevent the work from rising with the needle. Preparing the Sewing The same sewing preparatory procedures are used for the 7-33 as for the 31-15 sewing machine, except there is no knee lifting device. The hand presser bar lifter is the only device provided for lifting the presser foot on the class 7-33 sewing machine. Removing the Work Stop the machine and raise the thread take- up lever to its highest position. Draw about 3 inches of thread through the thread retaining disks. Raise the presser foot and draw the work back, cutting the threads close to the material. Leave the ends of the threads under the presser foot . Modification of Presser Foot for Webbing Sewing The modification of a presser foot is illustrated in figure 9-23. The presser foot should be cut 239.280 Figure 9-23.—Modification of presser foot for webbing sewing.







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