Timing the Movement of the Needle Bar Frame

NOTE: Rotate the eccentric no more than about 1/16 inch, then tighten its setscrews and check for results. Timing the Movement of the Needle Bar Frame Set the zigzag knob for straight stitch. Turn the handwheel and observe the travel of the needle into and out of the needle slot in the throat (needle) plate. If the needle is not centered in the slot, make the adjustments that have been described. Now adjust the needle to produce the widest zigzag stitch. Turn the handwheel toward you and observe vibration (sidewise movement) of the needle bar. The needle bar, on its upward movement, should begin to vibrate when the point of the needle is no less than about 3/32 inch above the throat plate, and should stop vibrating when the needle has reached approximately the same position on its downward movement. To adjust the vibration of the needle bar on model 99R, loosen the setscrews (H of figure 9-51) in the vibrator cam and slightly turn this cam on its shaft. Tighten the setscrews and check for results. On model 99R-3, the vibration of the needle bar is produced by a plate cam located at R on figure 9-51. Loosen its setscrews and slightly turn the cam on its shaft, following the same procedure as outlined in the preceding paragraph. Be sure to retighten the setscrews. To Raise or Lower the Feed Dog When at its highest position, the feed dog should usually rise above the throat (needle) plate the full depth of the teeth. To adjust the position of the feed dog, loosen screw (J of fig. 9-50) and raise or lower the feed dog; then tighten the screw. When raising or lowering the feed dog, be careful that its underside does not drop so low that it strikes the hook. 239.461 Figure 9-52.—Adjusting thread take-up spring. Adjustment of the Thread Take-up Spring The thread take-up spring (K of fig. 9-52) should be set so that when the eye of the needle reaches the material on the downward stroke, the spring has completed its action and rests against the top of the thread take-up spring regulator. If the thread take-up spring is not correct, loosen setscrew (L of fig. 9-52) and turn the tension stud (M) to the left for reduced movement of the spring, or to the right for more movement. After the take-up spring is set correctly, tighten setscrew (L). Regulation of the tension of the thread take- up spring (K) is done by turning the tension stud (M) to the right to increase tension or to the left to decrease it. Tension of the spring should just be enough to take up the slack of the needle thread until the eye of the needle reaches the material on its downward movement. 9-39