Feed mechanisms

Besides the basic motion of needles, loopers and bobbins, the material being sewn must move so that each cycle of needle motion involves a different part of the material. This motion is known as feed, and sewing machines have almost as many ways of feeding material as they do of forming stitches. For general categories, we have: drop feed, needle feed, walking foot, puller, and manual. Often, multiple types of feed are used on the same machine. Besides these general categories, there are also uncommon feed mechanisms used in specific applications like edge joining fur, making seams on caps, and blindstitching.

Drop feed involves a mechanism below the sewing surface of the machine. When the needle is withdrawn from the material being sewn, a set of "dogs" is pushed up through slots in the machine surface, then dragged horizontally past the needle. The dogs are serrated to grip the material, and a "presser foot" is used to keep the material in contact with the dogs. At the end of their horizontal motion, the dogs are lowered again and returned to their original position while the needle makes its next pass through the material. While the needle is in the material, there is no feed action. Almost all household machines and the majority of industrial machines use drop feed. Differential feed is a variation of drop feed with two independent sets of dogs, one before and one after the needle. By changing their relative motions, these sets of dogs can be used to stretch or compress the material in the vicinity of the needle. This is extremely useful when sewing stretchy material, and overlock machines (heavily used for such materials) frequently have differential feed.

Needle feed moves the material while the needle is in the material. In fact, the needle may be the primary feeding force. Some implementations of needle feed rock the axis of needle motion back and forth, while other implementations keep the axis vertical while moving it forward and back. In both cases, there is no feed action while the needle is out of the material. Needle feed is often used in conjunction with a modified drop feed, and is very common on industrial two needle machines. The advantage of needle feed over drop feed is that multiple layers of material, especially slippery material, can not slide with respect to one another, since the needle holds all layers together while the feed action takes place. Household machines do not use needle feed as a general rule.

A walking foot replaces the stationary presser foot with one that moves with the feed. A machine might have a single walking foot, or two walking feet with alternating action, and either drop feed or needle feed might be used as well. Walking foot feed is most often used for sewing heavy materials where needle feed is mechanically inadequate. It is also helpful with spongy or cushioned materials where lifting the foot out of contact with the material helps in the feeding action. Only a very few household machines have a walking foot, but this type of feed is common in industrial heavy duty machines.

Factory machines are sometimes set up with an auxiliary puller feed, which grips the material being sewn (usually from behind the needles) and pulls it with a force and reliability usually not possible with other types of feed. Puller feeds are seldom built directly into the basic sewing machine. Their action must be synchronized with the needle and feed action built into the machine to avoid damaging the machine. Pullers are also limited to straight seams, or very nearly so. Despite their additional cost and limitations, pulling feeds are very useful when making large heavy items like tents and vehicle covers.

Manual feed is used primarily in freehand embroidery, quilting, and shoe repair. With manual feed, the stitch length and direction is controlled entirely by the motion of the material being sewn. Frequently some form of hoop or stabilizing material is used with fabric to keep the material under proper tension and aid in moving it around. Most household machines can be set for manual feed by disengaging the drop feed dogs. Most industrial machines can not be used for manual feed without actually removing the feed dogs.

Finally, we turn to zig-zag and decorative stitches. Household machines perform only lockstitch, but almost all of them can do so in many different directions. By moving the needle from side to side, and changing the feed direction and distance, both fancy and utilitarian patterns can be sewn. The simplest example is zig-zag, where the needle moves to the left for one pass through the material, then to the right for the next pass. A household "blind stitch" takes several stitches in a straight line followed by one stitch to the right, then back to the original line. In older machines, the needle and feed motion is controlled by mechanical cams. Some household machines even offer a slot for user-replaceable custom stitch cams. In more recent designs, the needle and feed motion is controlled by electric motors. By adding controlled motion of the material being sewn through an additional set of motors, arbitrary customized patterns of 100 cm or more in each direction can be sewn, opening the door to the very popular category of programmable household embroidery machines.

While even extremely basic household sewing machines have zig-zag and a small selection of other stitch patterns, industrial machines do not. Industrial zig-zag machines are available, but uncommon. There are essentially no fancy-pattern stitching industrial machines, other than dedicated embroidery and edge decoration machines. Most industrial machines sew only a straight line of stitches. Even something as simple as a bar-tack or a buttonhole stitch is usually done by a dedicated machine incapable of doing anything else. When a variety of decorative stitching is required rather than a single stitch, a "commercial" machine (basically a heavy duty household machine) is usually employed.