The Why of Sewing 6: Sewing with Knits
I want to start off with apologizing for the long break between posts. Life gets in the way of crafts sometimes.
I previously wrote about the anatomy of knit fabrics here and if you haven't read that post, I highly recommend giving it a look. In the post I do briefly touch on some of the pitfalls many of us run into when sewing a knit fabric. In this post I want to discuss more about how to sew with knits and why anyone might want to do that to themselves. I will specifically be talking about sewing knits with a regular machine, not a serger. Serging may very well be its own future post.
The first pitfall many sewists run into when they attempt to sew on a knit is thread nesting. Image Source.
The image here shows nesting on a woven fabric, but the nest looks the same regardless. Thread nesting can have several causes, but on knits it is almost exclusively caused by sewing a knit with the incorrect needle type. Thread nesting in knits is caused by flagging, which is a fancy name for when the needle pushes the fabric down into the machine rather than piercing the fabric with each stitch. When the needle pierces imperfectly the bobbin thread loops around but does not catch the top thread and as you go on the problem worsens with every stitch.
There are several types of needles that work well with knits. For a basic jersey with little or no spandex added a ballpoint (or jersey) needle will be sufficent to solve the problem. For stretchier fabrics like swim knits I recommend a stretch or super stretch needle. If neither of those work, I recommend trying a microtex needle, which is extra super duper sharp. A microtex will damage the fibers going through, but for some knits, it is the only option that will work on a regular machine. Personally I keep stretch needles on hand and they tend to work on the widest range of knits that I work with.
Another problem with knits, or any other kind of stretchy or mobile fabric is the machine eating your fabric a the beginning of a seam. This is usually because the feed dogs don't have enough purchase and the edge of the fabric has more mobility and all the fabric is getting shoved down or shredding at the beginning. I have THREE solutions to this problem.
1. Take a small scrap of a more stable fabric, fold it in two layers, start in the middle of that and butt your project right up to the edge so the feed dogs and needle pass smoothly from the leader to your actual fabric.
2. Start your seam about 1/4 inch in from the edge of the fabric. This is generally better for seams that will later be intersected by other seams for stability. It is quick and dirty and generally works very well for more stable knits.
3. take a small scrap of tissue paper and put it under the leading edge of the seam, just for the first half inch or so.
The third major pitfall of sewing knits is stretching the seams. The first prevention for this is careful handling. When you have cut your knit fabric try to avoid letting the fabric dangle (this is also true of woven fabrics. Gravity is not your friend). Make sure you are not pulling and tugging the fabric through the machine. Some machines may need you to keep a hand in front and behind a seam to keep things from misbehaving, but it is important not to pull or stretch while doing so, just hold the fabric gently taut. Check your manual and see if your machine has a mechanism to reduce the foot pressure. Not all machines have this feature. The next two solutions do cost a bit of money. A walking foot is a specialty foot that has feed dogs above the presser foot so that the fabric travels through the machine with feed dogs on top and bottom. This is fantastic for working with knits and a walking foot is also useful for loosely woven fabrics, shifty fabrics, and for quilting. They are a bit expensive, and it IS important to get one that is compatible with your machine, however I consider a walking foot an essential investment in my sewing practice. Finally, consider picking up a roll of water soluble seam tape. The name brand is called Wonder Tape, although there are many off brands (I recommend Wawak's version if you are in the US or Canada). This is a double sided tape that fully dissolves in the wash. You use it to baste the fabric in place and also to support and stabilize the fabric while you sew. It is a little annoying that you will have to wash your knits before wearing them when you use wonder tape.
Sometimes, even with all these precautions you will still have a wavy seam or hem on your knit project. Do not despair. Many slightly wavy seams will relax on the first wash. Don't chuck it in the trash till you've chucked it in the wash.
And with that, its time to talk about our seams. Do not sew your knits with a straight stitch. I repeat, do not sew your knits with a straight stitch. Straight stitches do not stretch, the fabric will stretch. Even the most unstretchy knit still has mechanical movement and this movement will cause the seam to break. Unless your machine only sews straight stitches you have options for how to sew your knit seams. For y'all with straight stitch machines... maybe stick with wovens for now? My machine (and every machine I've ever owned) has at least 4 options that are recommended for sewing knits. On some machines you may need to adjust the top tension to get a good stitch on knits. Always test stitches on a scrap of your fabric so that you don't have to unpick failed experiments out of your actual garment. The image below is the stitch options for a Janome MOD30 machine (a machine I have owned and enjoyed).
1. lightning stitch (05 in the image) - This is a very narrow zizag that basically overlaps itself its so narrow. It is semi stretchy and generally recommended for sewing knits. I hate it. It doesn't pop but its very stable and so it can make the seams bind up on garments and it is an utter bitch to seam rip it. Also most machines don't center it on the foot and I hate that too. I am a lightning stitch hater.
2. triple stitch (04 in the image) - This is a stitch pretending to be a straight stitch. It is unlikly to pop, but also not stretchy. The needle is just going forward one, back one, and then forward one again for each stitch. I use it for topstitching tshirt pockets and that's about it. It also can be used on wovens to make regular thread look nice and chunky like faux topstitching thread.
3. Zigzag (06 in the image) - you want to set your machine to do a small and narrow zigzag but this is usually the best and most flexible option for constructing your seams. You can hem with this, but I think it tends to look a little too homemade for my taste.
4. triple zigzag (07 in the image) - this is the GOAT for flexible and stretchy topstitching on a knit. I think its a bit wide for construction but as a * sensory * human I prefer most my seams to be topstitched down and ALL my seams on close fitting garments must be topstitched down. Triple zigzag is fantastic for hems and its the ONLY option I have found that holds up to any amount of kid abuse, although I've not found a treatment that won't pop when a kid inserts their entire body into the hem of a tshirt and stretches it out to its fullest extent.
For a mock coverstitch/RTW look you can also use a twin needle for hems (NOT CONSTRUCTION) which has some stretch but is one of the most fragile options for hemming a knit. For instruction on how to use a twin needle I will refer you to your sewing machine manual.
Many patterns for sewing knits have narrower seam allowances than those used for woven fabrics. Most knits do not fray (please check!) and so the seams don't need to be finished. Knit patterns typically have either lines for the grain (see the fabric anatomy post) OR lines for the Direction of Greatest Stretch or DOGS. On most knits the DOGS is perpendicular to the grain (but not all!). Different knits have a different amount of stretch and a good pattern will give a range of stretch percentages that will be appropriate. Going for a higher stretch is usually okay, go down at your own risk. I have printed the measurement tool at this link and have it laminated in my sewing room.
I would recommend spending some time playing with the tool and measuring the stretch percentage of various knit fabrics around your house. In addition to the amount of stretch it is important to consider how much a fabric bounces back after the stretch is released. Cotton lycra with a low spandex percentage will often stretch initially, but may not bounce back after wearing for a while. This is called recovery and is especially important on garments that fit close to the body. I have unintentionally made several pairs of saggy underoos due to forgetting to consider recovery. Much like woven fabrics you should consider how much drape the fabric has when choosing it for your project. Buying knits is in my opinion more difficult than buying wovens. I have often purchased a knit fabric for one purpose and needed to pivot my plans once it arrived in the mail. Sadly I think the solution for this is to be flexible when working with knit fabrics (or be lucky enough to be able to buy knits in person I guess).
Okay, you might be thinking at this point, why the hell do I even want to try sewing a knit. Well the same thing that makes knits a pain in the ass to sew also makes them easy to wear and even easier to fit. Some garments just do not work in a woven fabric - yes it is absolutely possible to make woven undergarments, but do you actually want to wear them?
The things I personally make with knit fabrics are tshirts, underwear, bralettes, leggings, sweatshirts, sweatpants/joggers, kid pajamas, swimwear, and anti chafing shorts for under skirts. Its a part of my wardrobe, but not ALL of my wardrobe. If you are someone who finds themselves wearing mostly knit clothing, I might recommend looking into the purchase of a serger as part of your arsenal sooner than the average sewist. If you try working with knits and hate everything about the experience, I recommend you stick to sewing what you like and find a RTW underwear brand you like.
