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Seams and Hems
It is best to determine what kind of seams and hems are most appropriate for your type of knit and your particular project before you start tackling the construction of your garment. Experiment with both your sewing machine and your serger.
Types of Seams
There are so many ways to seam knit fabrics and because knits don’t ravel, you won’t even need to clean finish the raw edges. You can use your sewing machine, your serger, or a combination of both machines.
Sewing Machine Seams
There are four basic sewing machine seams suitable for knits: straight stitch, double-stitched, zigzag stitch, and programmed knit stitch.
• Straight stitch seam. This is the simplest of all of the seam options. Stitch a line of straight stitches along the seamline. Press the seam open. Use this seam for garments that are semifitted or loose-fitting, garments that don’t have a lot of strain on the seams.
• Double-stitched seam. Stitch a line of straight stitches along the seamline. Stitch a second row of stitching 1/4" (6.4 mm) from the first line, in the seam allowance, and trim close to this line of stitching. Use this seam when the edges are curling and preventing the seam from staying flat.
• Zigzag stitch seam. Start with a machine zigzag setting of 0.5 mm (.02 inch) wide by 2.5 mm (.10 inch) long. The settings may vary with the weight and type of fabric. Use this seam for garments that are close fitting and need to stretch during wearing.
• Programmed knit stitch. This stitch is similar to the zigzag stitch, but the length and width are automatically set in the sewing machine software. Some distortion might occur because it is sometimes difficult to make machine adjustments. Use this stitch for garments that need to stretch during wearing. It is a difficult stitch to rip out so make sure it is your final stitch.
Samples of four sewing machine seam finishes (from top): Straight stitch with seam pressed open, double-stitched, zigzag stitch, and programmed knit stitch.
Overlapping Seams
This specialized seam type is used on thick knits whose edges look good when left raw. Fabrics such as felted wool and wool-blend bouclé are the perfect fabrics to sew with overlapping seams in order to reduce bulk.
1. To sew an overlapping seam, first cut away the seam allowance from the edge of one of the garment pieces (the edge that will overlap). Use fabric chalk to mark a line indicating the seam allowance on the corresponding garment edge. Place a strip of double-faced craft tape within the remaining seam allowance, then remove the paper to expose the adhesive (A).
2. Place the trimmed edge over the taped edge, matching the raw edge to the chalk line, and finger-press it in place. Edgestitch along the raw edge. Remove the tape and stitch 1/4" (6.4 mm) from the first stitching (B).
3. Trim the excess seam allowance on the wrong side of the seam (C).
Finished jacket with overlapping seams.
Combination Seam
If you prefer to clean finish raw edges for a more polished look, the simplest option is to first sew a seam using any of the standard sewing machine seams. Then finish the raw edges together with a three-thread serger stitch.
This seam and seam finish can be used on any type of garment, including tops, pants, jackets, and dresses. It tends to be most appropriate for midweight knits or knits that don’t ravel but don’t really look very good with edges left raw, such as novelty and sweater knits.
Serged Seams
Serging is often referred to as overlocking because a serger actually produces an overlocking stitch. All sergers are different, but most can sew a two-, three-, or four-thread stitch. Some sergers can even sew a five-thread stitch (three-thread overlock stitch with a two-thread chain stitch). The most common serger stitches used on knits are three- and four- thread stitches.
Three-Thread Stitch
The finer three-thread stitch uses threads in one needle, the upper looper, and the lower looper. It is the perfect choice for seams on tissue-weight knits, airy laces, and open weave knits in fairly loose-fitting garments. Otherwise, it is used as the raw edge finish in the combination seam for all other types of knits.
Four-Thread Stitch
The four-thread stitch combines threads in two needles, the upper looper, and the lower looper. With the additional needle thread, the stitch is more hard wearing than the three-thread stitch and can be used to stitch construction seams and is rarely used in combination seams. As a sturdy stitch, it is often the choice for athletic wear, children’s clothes, and garments such as T-shirts that are close fitting and are worn and laundered often.
Flatlocked Seams
A flatlocked seam is a reversible serged seam that features loops on one side and ladder stitches on the other. The edges of the seam are butted together rather than overlapped. A two-thread flatlock is particularly suitable for use on stretch lace and other open-weave fabrics that are too bulky to sew conventionally because the ladder stitches blend into the weave of the fabric and are almost invisible. It is not a suitable seam for fabrics that ravel.
Not every serger is capable of flatlocking because it is done with only two threads (one needle and lower looper) so the upper looper needs to be blocked or deactivated. Refer to your owner’s manual.
To stitch a two-thread flatlock, use the left needle and set the lower looper tension to 5.0 or looser. Use a 2.5 mm (.10 inch) stitch length, a 3.5mm (.14 inch) stitch width, and set the differential feed between 1.5 and 2 mm (.06 and .08 inch).
Engage the cutting knife to cut off the seam allowances as you stitch. Once you have stitched the seam, remove the garment from the machine and turn the work to the right side, gently spread the seam until it is flat. This allows the loose stitches to form a ladder on the right side of the fabric connecting the two seam edges.
Stabilizing Seams
Certain areas of a garment may need to be stabilized to prevent them from stretching out when the garment is hanging or being worn. Areas that usually need attention are necklines, shoulder seams, and waistlines.
The easiest way to stabilize these areas is to use narrow strips of fusible tricot. You can either cut 1/2"- (13 mm)-wide strips from yardage or purchase it precut. Since tricot is a knit and has some give, the stabilized areas are controlled to some degree while allowing some natural movement of the garment.
When a garment requires stabilizer, center the strip over the seamline on the wrong side of the fabric. Fuse the strip in place. Then sew the seam, catching the tricot in the stitching. At the shoulder seams, a strip is needed only on the back piece.
Types of Hems
Hemming a knit garment is almost always the last step, so it’s very important to select the right type of hem for your knit and to execute it well.
Unturned Hems
Leaving a hem unfinished used to be a sign of poor quality, but many high-end designers are utilizing the nonravel advantage of knits as planned finishes in designing knit garments. You can leave the cut edge as it is or serge it.
A serged edge is generally a hidden finish, but a carefully stitched line of serging is a perfectly acceptable finished hem choice. A serged edge adds polish without adding bulk and eliminates the challenges of machine stitching a hem on a knit garment.
Turned Hems
Most hems are turned to the wrong side in some fashion and may be finished or unfinished on the wrong side of the garment.
Single-Fold Hems
Use one of the two techniques for marking perfectly even hems or simply measure and pin a hem in place. Once the hem is folded one time to the wrong side, it is ready to stitch. Here are five stitch choices:
Straight Stitch (sewing machine)
A straight stitch (A) is simplest and most invisible. Leave the edge raw or finish it with a three-thread overlock stitch formation. This hem is used on garments that are semifitted to loose fitting. Straight stitches on fitted garments can pop open when the garment is stretched.
Zigzag Stitch (sewing machine)
A small zigzag stitch (B) allows the fabric to stretch without popping stitches. Experiment with length and width settings; a good place to start is with a 2.5 mm (.10 inch) length and 1.5 mm (.06 inch) width setting. This is a good stitch to use when making a fitted garment.
Double Needle Stitch (sewing machine)
A sewing machine double needle has two needles on a single shaft, so it requires two upper-thread sources and one bobbin thread. Double needles feature a variety of widths between the two needles, from 2 mm to 4 mm (.08 to .16 inch). This type of needle produces two rows of straight stitches on the right side of the fabric and a series of connecting zigzag-type stitches on the wrong side. This stitch does resemble a common ready-to-wear hem, except it does not cover the raw edge on the inside hem edge and the stitches don’t stay flat, they tend to produce a tunnel between the row of stitches (C).
Coverstitch (coverstitch machine)
A coverstitch looks like a double needle stitch with two rows of straight stitches on top and connecting stitches on the bottom, but this stitch is flatter, covers the raw edge of the hem and looks the most professional of all of the hem stitch options.
Blindstitch (serger)
A blindstitch produces a smooth hem, invisible from the right side of the garment. It requires a special blindhem presser foot (A), which can be adjusted to barely catch the outer fabric, while overlocking and finishing the inner raw edge at the same time (B).
Double-Fold Hems
Occasionally, lightweight sweater knits and other novelty textured knits don’t have smooth and attractive looking raw edges. These knits tend to look better with double fold hems. You’ll want to test a double fold hem on a fabric scrap to make sure it is not too bulky.
1. Stitch the same distance from the edge as the width of the final hem. Press the hem to the wrong side using the stitching as a pressing guide (A).
2. Move the needle position to the right. Turn the hem a second time, the same distance as in step one, and don’t press it. This is a turn-as-you-go hem, so start stitching along the inner folded edge, turning the hem as you stitch. Leave the needle down as you reposition and turn the hem as you advance the stitching to complete the hem (B).
Designer Hems
In addition to raw edges and traditional turned hems, the racks are full of knit garments that feature creative edgings.
Selvage Hems
Many knits have novelty selvages, perhaps ruffled or woven with a contrasting thread (A). This is particularly true on lacey and other open and textured knits. There are a few hem techniques that showcase these novelty edges.
One option is to incorporate a selvage in the design of the garment, planning its placement and using it as a substitute vertical or horizontal hem depending on the direction of the stretch (see opposite).
Another option is to cut away the selvage and then reattach it in another location.
When planning to use a selvage in another place, cut off the selvage, leaving some additional fabric width to work with later. In most circumstances, a selvage can be added back using flatlocking (B). See here for flatlocking instructions.
Lettuce-Edge Hems
Lettuce edges are wavy edges that can be sewn on a sewing machine or a serger. Refer to your machine manual for the specifications. They are particularly suitable for jersey, a fabric that naturally curls to the wrong side on the crossgrain when it is stretched.
Set your machine for a wide enough zigzag stitch to cover the curly edge of the fabric; pull the fabric as you sew. When you pull the fabric as you sew, it curls, and the zigzag covers the curly edge. As with all decorative treatments, experimenting with settings is essential.
Lettuce edges made on a sewing machine (top) and a serger (right).
A finished garment with a lettuce-edge hem.
Bound-Edge Hem
When sewing heavy fabrics such as sweater knits, the fabric may be too thick to turn and stitch, so binding the edge is a great solution. The binding material should be a nonbulky knit.
1. Determine the desired finished width of the binding. Cut the binding knit on the crossgrain four times the desired finished width by the length of the edge, plus a few inches (cm). You might have to join several widths of the binding to obtain the necessary length.
2. With right sides together, stitch the binding to the edge of the garment and then stitch the narrow ends of the binding at the point at which they meet (A). Trim away excess binding.
3. Fold the binding over the raw edges, pin, and then stitch in the ditch, catching the binding fabric on the wrong side (B).
4. Trim the excess fabric near the stitching on the wrong side (C).
