If there is any alteration required in the time of the rotary hook referred to, it can be made to the smallest fractional part of an inch very quickly and easily, and the movement can be relied on. The shaft to which it is secured is positive in its action (no variable motion), and at every stitch will meet the needle at exactly the same spot. This is an improvement over the boat-shaped shuttle, which has to have a certain amount of play or slackness to allow the loop to extricate itself; and this slackness increases as the machine is worked, so that the shuttle action often becomes very erratic.
Sometimes a carrier becomes sprained at one end, thus allowing the shuttle too much freedom. If at the heel end, the carrier should be removed and placed in a vise (heel uppermost). The heel should be given a light blow with a hammer, thus bending it into correct position, but it must never be allowed to incline toward the shuttle; it should stand perfectly square, and have the upper corners rounded off. If inclined toward the shuttle, the loop may occasionally hang on the heel, and cause an irregular tension.
Fig. 97. Bobbin case holder
In some machines the bobbin case holder ([Fig. 97]) rests on the casting seen in [Fig. 81]. It is secured by a large set screw, D ([Fig. 97]). For general use, this screw should be adjusted to allow number 40 cotton to pass freely over the bobbin case. The holder should not be removed, except when adjustment or repair is needed. The vertical portion is hinged to the base, and is kept upright by a lock spring and stud. If the spring is pressed from the stud, the vertical or ring part can be drawn back for placing in or taking out the bobbin case. The face of this portion must be perfectly square with the bottom of the base, otherwise it may cause considerable trouble. A slight adjustment can be made by loosening the two screws and moving the lock spring. A set square, E, should be used for testing the accuracy of this part as shown ([Fig. 98]), F representing the bobbin case holder.
Fig. 98. Set square
The thread controller is similar in design to several others, but its movement is regulated by a small lever ([Fig. 99]) which receives its motion from a link attached to the foot bar bracket set screw, and this may be seen through a hole in the face plate. At G ([Fig. 99]), this lever engages with a stop washer located behind the thread controller plate. The washer is recessed to form a stop, at the same time to give sufficient clearance for the action of the spring; thus as the foot bar rises and falls, so does the thread controller spring. It is a common practice when cleaning a machine to remove the face plate, thus detaching the link referred to, and not connecting it again when replacing the face plate. From this, trouble arises. The tension pulley should be placed on its stud, the large boss being toward the face plate.