Adjusting the Feed Dog The height at which the feed dog should be set depends on the weight and number of plies of the material being sewn. If the feed dog is set too low, the material does not feed through the machine; if it is set too high, it may cut or fray the material. The recommended height of the feed dog for sewing lightweight canopy material is slightly less than one tooth above the throat plate. If you are sewing heavier material, raise the feed dog to a height that ensures positive feeding of the material. After you have decided on the correct height for the project you are working on, adjust the feed dog accordingly, by loosening and then tightening the screw, as shown in figure 9-7. You must remember that each time the height of the feed dog is changed, the feeding mechanism may be out of time. For this reason, set the feed dog first, and then make the necessary adjustment on the feeding mechanism. Since most of your canopy repairs involve material of approximately the same weight, one-time adjustment of the feed dog is usually sufficient. Repeated changing of its height is not necessary. Adjusting the Thread Take-up Spring To adjust correctly the take-up spring in the tension assembly (fig. 9-8), you should first understand its normal operation. The thread take- up lever pulls the thread take-up spring down about even with the slack thread regulator while the needle is going up. While the take-up lever is coming down with the needle, the thread take- up spring pulls the slack out of the thread and keeps it from getting under the needle. If you do not have this adjusted properly, a loop can form 239.445 Figure 9-8.—Tension assembly. over the needle hole in the throat plate, and the needle can split the thread as it enters the needle hole. You should set the spring about 1/4 inch above the slack thread regulator. The thread take- up spring should be set so that the spring will have completed its downward motion and be resting on the stop when the needle, on its downstroke, reaches the fabric. To adjust the spring, loosen the setscrew, as shown in figure 9-8. To put more tension on the spring, you turn the assembly clockwise; to put less tension on the spring, you turn the assembly counterclockwise. It may be necessary for you to replace the thread take-up spring because it can bend and become weak. Loosen the setscrew and insert a screwdriver into the slot of the tension screw stud (fig. 9-8). Turn the stud to the left until it is screwed out of the thread take-up spring regulator. Remove thumb nut (fig. 9-8), the tension spring, and tension discs. The take-up spring is now free for removal. After replacing the old spring with a new one, assemble the parts in reverse procedure. Replacing the Needle While replacing a needle is a relatively simple job, you must know a few things about needles in order to decide which needle is required when a needle must be replaced. It is very important that the proper needle be used to ensure good machine operation. The selection of needles by class, variety, and size for different machines and materials is necessary to eliminate thread breakage, needle breakage, skipped stitches, and fraying of the thread. Needles for the various machine classes are selected and ordered by needle number and size. The needle numbers consist of a class number and variety number separated by a‘‘x”; for-example, the class and variety needle 16 x 87 is used in the 31-15 sewing machine. Cloth point needles are round, sharp-pointed needles used for sewing cloth, since they do not cut the strands as they are forced between the woven threads of the fabric. Many different varieties of cutting point needles are available, but they are used only for sewing heavy leather. Figure 9-9 shows the shape of the openings made in material by the cloth point (view A), twist point (view B), and the diamond point (view C). Figure 9-9 illustrates why it is important that a round-pointed needle be used in cloth; views B and C show how cutting point needles can cut the warp and filler threads. 9-8