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I am a mother, a grandmother, and a teacher. But whatever happens in my life, I keep sewing. I have worked as a political communicator and now as a teacher in my formal life. I have also written extensively on sewing. I have been a frequent contributor and contributing editor of Threads magazine and the Australian magazine Dressmaking with Stitches. My book Sew.. the garment-making book of knowledge was published in May 2018 and is available for pre-order from Amazon



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Thursday, November 2, 2017

Sewing and hemming knits Exhibit A

I love sewing knit garments and I love wearing them. 

Fast to sew and comfortable to wear - this just about covers it for me in terms of everyday clothes.

But let's face it.

There is one area that can be challenging to me and that is hemming.

I decided to get to the bottom of this issue and share my experiments, one by one, with you for comment.

As a baseline let's talk about what there is to know about knits and knit hems:

1. Knit fabric stretch - this is not helpful on hems that, in the process of hemming, can be stretched out of shape.

2. Straight up straight stitches, composed of the famous lockstitch, which is essentially a tiny knot in each stitch and not at all mobile when lined up in a seam, can break when the fabric stretches and it can't. I think it is safe to say that pretty much nothing terrifies a sewer like the idea that one of their own stitches should ever pop.

However we also know a few other things too, one of the most significant being that any zig-zag stitch is by nature somewhat stretchy.

Now this is a fact - compare what happens when you pull on a zig-zag stitch and when you pull on a straight stitch - although I can't actually tell you why this is so.

If I had being paying attention in the one and only year I took physics I might be able to say that the diagonals deflect the stress - but since I was not paying attention you and I would both know I was making this up, although like many made up things it does seem reasonable. 

Note I did take Latin instead of sciences - it was that kind of school system - on some argument that if you knew Latin you had a basis for other languages - logic that has left me with no other languages, no knowledge of science, and but lots of made up ideas about zig zag.

Back on track.

What does matter here, and is true, is that a hem made with zig zags will not break very easily. This is why many traditional patterns, and some companies like Jalie that have a long pre-serger history, suggest hemming with a zig zag stitch.

So as my kick off hem that is exactly what I did on this excellent sweatshirt pattern by Jalie:

I have to say that I really love this pattern. I bought it as a basis for the kids' Halloween costumes for which I needed various bottoms and tops, such as this Batman for Billy:

It kills me that I can use the same pattern for Billy and for myself.

In my version I left off the band at the bottom, I was doing a hemming experiment after all, and I curved the side of the hem.

I serge finished the raw edge of the cotton/lycra sweatshirt fleece, and then turned it up and stitched it with a large zig zag using sewing thread.

Here is what the stitched hem looks from each side laid next to each other:

And here is the sweat shirt on my dress form, since this project was a one person operation today and I am unable to both wear the outfit and photograph it at the same time. I notice my dress form has a bit of a list to her in these shots, undoubtedly because I bashed her around a bit on the stairs when we came up from the basement:

As I suspected it would this hem does have a wave to it. The reason for this is of course due to another aspect of the zig zag stitch applied to a knit fabric - the busy action of the zig zag can work the fabric a bit and under that activity stretch the fabric out somewhat and then sew that stretch in.

This is exactly why I am not a fan of all those multi-action reverse action "stretch" stitches on so many machines - too much movement=too much fabric stretch. A minimal old zig zag is about the only stitch like this I would ever use to make a knit hem.

To recap, so here we are:

Zig zag hems on a conventional machine with conventional thread:

  • Not likely to pop the stitches
  • Familiar machine, familiar stitch, easy to implement. You don't have to get up out of your chair, which has a lot going for it.
  • The hem may wave - the degree of wave in proportion to the degree of stretch in the fabric
Grade: B- to C+ which is a pass of course. Anyone who teaches or anyone who takes a course is very clear on this.

On my body this hem looks maybe more normal that it might to you now when you are looking at it on a dress form with an eagle eye for any faults.

More ideas tomorrow. 


Elle said...

Is the wave limited to the curvy area of the hem? Or is it is a problem overalll? (Can you tell I don't sew with knits?)

jirons42 said...

I am really interested in this topic and looking forward to tomorrow's blog.

SewRuthie said...

I was often disappointed with the hems on my knits so I bought a coverhem machine. It is fab, though a bit single use.

Vanessa Keen said...

Have you tried lightly ironing the seam with lots of steam? It can help to bring the stitches back into shape.

Anonymous said...

I wonder about a steamy ironing session, too - maybe not feasible given the content of the fabric?


Jean said...

Thank you for this series. I am saving up for a coverstitch machine-earning the money by making pillows for an interior designer. Deadly boring, but I'm getting to my goal!

I love sweatshirts, but find RTW difficult-have a round figure and short arms. I want to make my own, and so I will follow this series with great interest.

Kathie said...

Great topic! Do you suppose that a layer of tissue paper between the hem and the feed dogs might mitigate the stretching issue?

Joanna said...

I think the physics in zigzag stitches is that there is more thread length than there is hem lenghth. I'm not sure if my 3 years of Latin enabled me much either in being multilingual but it did help me learn important phrases like'Dos cervezas, por favor'. I'm also interested in this topic, thanks for tackling it.

JustGail said...

My understanding of the zig zag is that every place that the upper and lower threads loop around each other acts as a hinge. And the wider & shorter the stitch length, the more flex the stitch has. But it also increases the chance for fabric distortion and need for a stabilizer of some sort.

I've had good luck using a very narrow zig zag, aka wobble stitch, and using Steam-a-Seam also helps. Although I think that has more to do with preventing layers shifting better than pins.
My sewing of late has been on lighter weight knits (poly or rayon spandex blends) than what you used on this example. How much does the fabric thickness and density affect the results of various hemming methods?

JustGail said...

One more thought - on this top, when you serge the edges, do you gather/stretch as appropriate on the curves? I've forgotten to do that and then when the hem is flipped up, I'm fighting the exact same issues as on wovens - not enough fabric at the side seam curves, too much fabric at the other curves, and get those exact hem waves. And those don't always press out for me.

celkalee said...

A very lightweight fusible interfacing will help stabilize those stretchy areas nicely. A strip more narrow than the folded up hem is all that is needed. Always test on your fabric, some knits don't care for fusibles but most seem to be OK with it.

Kay said...

Thank you for doing and sharing your knit hemming experiment. I'm sure I'll learn a lot!

1. I, too, wonder if a good steaming might flatten out the wave.

2. Do you think a walking foot might smooth out that wave? I haven't tried this yet, but I used my walking foot for the first time this week. I'm making a pair of underlined joggers and will use it to hem them today. I'll let you know how it goes.

3. I don't remember where I learned this - maybe Pamela's Patterns? - but if you press up the hem with a very light fusible before stitching it is much less likely to stretch.

4. The reason a zigzag stitch stretches is because when you pull on it, it goes from diagonal to the hem to parallel. So a 1mm diagonal stitch covers, say, 3/4mm when measured parallel to the hem. When stretched the stitch flattens out so that it is parallel to the hem, and that 1mm stitch covers 1 1/4 mm of stretched hem. I don't know if I've explained this very well. It would work better with pictures. :-(

Catherine said...

I am looking forward to hearing about your experiments. I mostly hem knits (and wovens) by hand using a stitch that I learned as a child but don't know the name of (you pick up a few threads from the fabric and then stitch on a diagonal into the hem). Now that I think about it, this creates a kind of zigzag stitch, though much larger than a machine-made one. I do not have stitches pop. I know lots of people don't like hand-sewing but I do and it's soothing to finish off a project with a bit of contemplative handwork. (I have been known to use a twin needle to hem knits but I find there's a little hump between the needles that I don't like and I just think an invisible hand-stitched hem is more elegant.) I guess machined hems are more "ready-to-wear" looking but I'm not really aiming for that. I have also experienced a wavy hem on a very stretchy knit that I machine hemmed and was unable to steam it out as suggested above ... but since it was wavy all around, I just decided it was a look...

Sasha said...

Love your theory about zigzag stitches, but I do think you are wrong. Apologies. Zigsag stitches are less likely to break because they pack more thread length into the stitching line. Zigzag stitches will still break if the fabric is stretched farther than the length of thread is able to accomodate. This is true of all the different ways of stitching hems. Perhaps a case for those glues discussed the other day?

Jalie patterns are a good value, aren't they? And an excellent illustration of drafting for different sizes. I was not surprised to learn that the designers are also mothers.

bespokeability said...

I use my Babylock Coverstitch machine to do hems on knits. It does a perfect job every time!

Cathie said...

Great topic! I really need this, and have several great knits on my cutting table. The last one, very curly (sigh) I added vintage flexi-lace, and hand hemmed. It looks great, but more help needed. Cathie!

paloverdeblooms said...

I love this topic and am so pleased you are making these experiments. My knit hems have always been by hand; by baby hem; or by doing two parallel rows of stitching (not double needle). I'll be interested to see all the ways you investigate.

Anonymous said...

I use hair permanent end papers (very thin tissue papers) under my fabric; a .5 x 3mm zigzag stitch with my IDT foot engaged. Have even had clients tell my knit alterations never break even after years of use. And I always use a double fold in a 3/4" size so my hems are weighted an don't flip up. I ALWAYS change rtw to this to avoid the usual flip up of a too narrow hem. Which I HATE!!
I always enjoy your musings, Renita in NC USA

Jean S said...

I am wearing a pair of knit pants that's at least 4 years old (been downgraded from good wear to walking/gardening). As I don't have a coverstitch machine (or serger), I sewed these with a narrow zigzag stitch. Not a single popped stitch.

Karen said...

Love this topic as I never got an A+ hem on a knit (don't have a overstitch) when using any method on a sewing machine. Since then, I just do it by hand with a herringbone stitch. I anchor the thread every 5 inches or so too that in case a stitch pops, you don't loose the whole hem. Doesn't take long and I enjoy hand sewing. Nearly completely invisible, so looks really good on more elegant garments.

Anonymous said...

As a sewist who almost exclusively works with knits and only has a basic machine, I've experimented with many finishes and typically prefer a zigzag hem. Admittedly, I haven't tried twin needling yet but that's because I've been satisfied with my hemming results enough to not bother with it just yet.

One thing I always do is a test run on the same fabric in the same grainline direction as the hem to be sewn. Some fincky knits require many tests but there is nearly always an ideal stitch for each fabric. Sometimes it requires higher tension, smaller stitches or wider zigzags. Some stretch ITYs only like specialty versions of triple zigzags. And very stable fabrics handle everything I throw at it, and it's just a matter of choice. (I really love those situations!) Taking the time to figure out how the fabric wants to be sewn is always worth it in the end.

This is why I can't subscribe to the idea of there being just ONE ideal solution to ALL hems, because fabric choice changes everything, every time.

Every once in a while, I get a slippery, drapy, flimsy, stretchy fabric that my machine just HATES. (This is usually RTW that I'm attempting to alter in some way.) Luckily, those usually end up looking fine unhemmed so I leave them alone and save that energy for another project.

I'm looking forward to learning more from this series. Thank you for posting it!

Galica said...

I'm going to weigh in on the theory side a little late in the piece. I'm not a physicist or even a scientist, though I did do a bit of science and maths at school and even explained it to other people at the local version of the exploratorium (but 30 years ago!).

When a fabric "stretches" there is no new material added - it's simply that material (ie, the thread) which was aligned more or less at right angles to the axis of stretch has been persuaded to move into alignment with the axis of stretch, giving more length. So, when you add length you remove width. (Who amongst us has not tried on an old bias cut skirt to delightedly discover that it still fits our hips, but is mysteriously much shorter that we remembered?)

A zigzag stitch sits diagonally to these two axes and so the stitches have the necessary material within them to move with the stretch.