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Pattern Making: Concave and Convex Curves

I don’t remember what or when I was sewing. All I remember was staring at the unfinished garment on the form and seeing that something looked funky and not right.

“What’s wrong… what’s wrong?” I thought, stepping back to get a “monet” of the garment (monet is Cher Horowitz’s word for glancing at something from afar).

The garment was pulling in all sorts of directions at the seam and the seam allowance was not lying flat.

“You dweeb! It’s a concave curve!” I said to myself.

Problem solved.

Defined in non sewing terms, a concave curve is a curve that is hollowed or rounded inward like the inside of a bowl and a convex curve is a curve that is rounded like the exterior of a sphere or a circle. An easier way to think of a concave and a convex curve is a concave curve is a valley and a convex curve is a mountain. Also, things that “vex” you tend to stick out and caves tend to be things that other things are stuck into (like belly buttons!).

When it comes to sewing, concave and convex curves present the biggest challenge when it comes time to press seam allowances.

Depending on whether the seam is a concave or a convex curve will determine whether to clip or to notch the seam allowance so that it lies flat. For both concave and convex seams, first trim seam allowances to 1/4″ after sewing. After, if the seam is concave, cut v notches at regular intervals so that when the seam allowance is pressed back towards the stitching line, it will lie flat. The reason why the seam allowance doesn’t lie flat if V notches are not made is because the length of the edge of the seam allowance is LONGER/GREATER than the length of the stitching line / when the seam allowance is pressed back towards the stitching line, the edge is too long in comparison to the stitching line.

If the seam is convex, clip into seam allowances notches, being very careful not to cut through seam.Β The reason why the seam allowance doesn’t lie flat if clips are not made is because the length of the seam allowance is SHORTER/LESS THAN the length of the stitching line / when the seam allowance is pressed back towards the stitching line, the edge is too short in comparison to the stitching line. CUTTING Β into the seam allowances and allowing it to FAN OUT increases the length.

Does this make sense? Most importantly, do you understand why clipping and v notches are made (because the length of the stitching line and seam allowance edge are different)?

25 Comments

  1. Reply

    Piper

    Is this done on mass produced woven clothing? I feel like I never see clipped seam allowances in off-the-rack clothing. Aren’t most edges serged? Is that done before or after clipping?

    • Reply

      Maddie Flanigan

      Piper,
      It depends on a lot – the fabric, the category of clothing, the brand, the manufacturer, etc. I’ve seen it done and not done. When I worked in technical design for jackets, it was pushed heavily on our manufacturers to clip/v notch but when I worked in knits, clipping/v notches was rarely done. One reason was because of the fabric (it’s easier to get away with NOT clipping or notching in a knit) but another is the knit business is VERY FAST PACE and corners are cut wherever they can be.

  2. Reply

    Miranda

    Totally makes sense, and not something I’ve ever considered! I always “clip” but never “notch” and of course it will lie flatter if there isn’t overlapping seam allowance in the curve. Now I’m going to give that scalloped hem a try again!

  3. Reply

    Natasha Estrada

    I tend to grade more aggressively usually 1/8″ or 3/16″ or one of each. I usually can avoid having to clip/notch. Grading with pinking shears help too. Grading the seam allowance aggressively also brings the length of the seam allowance and the length of the seam closer together. How compliant your fabric is to your demands will affect what you can get away /endnovel

    • Reply

      Maddie Flanigan

      Natasha,
      You’re absolutely right. With every rule, there are going to be exceptions, ESPECIALLY in sewing. As a general rule though, this is how you treat seam allowances for concave and convex seams. BUT there will be times when you don’t need to clip or v notch, an example being that if you clip seam allowances to 1/8″ or 3/16″ or if the fabric is knit. My most important point of the post was why clipping and v notching is done – because of the difference lengths (seam line v edge).

      • Reply

        Natasha Estrada

        Absolutely and your diagrams do an excellent job of illustrating that the whole point is to create or remove space so the seam can be the boss. Because it’s all about the seam y’know πŸ˜‰

  4. Reply

    TessaMelissa

    I remember the first time I had that “What happened?!?” panic attack after sewing a curved seam. As a mostly self-taught sewist, I clipped the seam allowance thinking I was fixing some sort of mistake I made while sewing. A “Make it work” moment, if you will. It was later that I discovered that it was actually common practice.

    • Reply

      TessaMelissa

      Oh, and the Clueless reference made my day. πŸ™‚

    • Reply

      Natasha Estrada

      LOL this reminds me of all the years I was “being bad” trimming the tops of my sleeves off to remove ease only to learn years later that it probably didn’t need to be there in the first place.

  5. Reply

    Christina

    I think the stitch line should be on the other side for one of them..
    This makes me so confused, thanks for making a post about it
    I always forget

  6. Reply

    Sewing Princess

    Thanks for the explanation. I normally clip but hardly notch. Do you think not notching is the reason why my bias bound neckline doesn’t lie flat? e.g. http://bombardone.com/sewingprincess/2012/09/a-sustainable-sorbetto-is-born/

    • Reply

      Maddie Flanigan

      I don’t think clipping/notching is an issue with your binding. From the photos, it looks like your binding is “roping,” which means your stretching it differently when you sew each pass. Also, the width of your binding is not helping either – it’s WIDE. Why don’t you try 1/4 inch?

  7. Reply

    Anna Depew

    Excellent post and so well explained! I knew to clip them but I never thought about the mechanics behind why! Thanks!

  8. Reply

    Gaby

    Your convex and concave images are currently the same, just rotated. The stitching line should be moved on one of them, I think it might be the concave one? If the stitching moves to the other side of the line, the edge will be concave.

    • Reply

      Maddie Flanigan

      No matter how many times I look at an diagrams I create, there is always something I miss. Thank you. The diagram has been updated πŸ™‚

  9. Reply

    Angela

    Great diagram and tutorial! I never know when to notch vs clip.

  10. Reply

    anto

    What a great explanation. I’ve had my share of headaches when sewing certain garments trying to figure out why a curve looked weird or down-right wrong. I usually do clip into the seam allowance but after years of sewing I have come to the conclusion that I will never shake of the fear of accidentally clipping the seam.

    A+ for sneaking in a Clueless reference πŸ˜‰

  11. Reply

    VickiKate

    Fabulous explanation Maddy! Thank you!

  12. Reply

    limescented

    Hi there,

    Thanks for the tutorial – and the other great drafting tutorials you’ve put up – but in this one, it seems that you’ve described the process in vice-versa for both situations?

    As you said, concave shapes are hollowed out. So in your diagram, the labeling should be reversed.

    Also, since concave shapes are hollow, the edge of the seam allowance is shorter than the length they’re required to span when the garment is turned right side out. Therefore, they need to be clipped, so that the fabric edge can fan out.

    And vice versa for convex curves – which need to be notched to remove extra fabric, since the edge of the seam allowance is longer than the length they’re required to span when the garment is turned right side out.

    I found a pictures of what I’m trying to explain here: http://sewmamasew.com/blog2/2011/10/the-hows-and-whys-of-clips-and-notches-sarai-mitnick-colette-patterns/

    • Reply

      Maddie Flanigan

      thanks for your callout but if you look at my diagram closely and follow along with my wording, I think I am correct (you are too – see why below).

      Concave curves ARE hollowed out like the inside of a BOWL (think cereal bowl) and this is how the concave curve in my diagram is drawn (if it was revered, then the bowl would be upside down).

      In the link you provided, the stitching lines and edges are reversed from my diagram, which changes the whether you should clip or notch.

      This is why I explained WHY you should clip versus notch…
      -If the edge is SHORTER than the stitching line – you have to clip
      -If the edge is LONGER than the stitching line – you have to cut v-notches

      Does this make sense?

  13. Reply

    Jo

    This is really dumb but my head just can’t get around stuff like this easily. It’s all “you want me to imagine objects?? Not happening”. I do get the concept of this, but I still have to keep relearning it cos it doesn’t stick haha. “Now, which was which again…?” Heh. πŸ˜›

  14. Reply

    Joanne

    I am a true novice in sewing. It’s quite the challenge . But, because of you Madalyne and all the sweet people here commenting, adding, suggesting etc. it is all slowly coming together. I’ve made a muslin of jeans. This was well worth it. Now i am doing the real thing but wanted to understand better about curved seams. I was doing a lot of research on how to finish inside seams as I want the inside as interesting as the outside. As mentioned, it’s because of all the people in this great community called the “net” that I am able to live a dream that I once only dreamed of. So a big and large thank you to you all.

    • Reply

      Maddie Flanigan

      What a sweet comment Joanne. Thank you!

  15. Reply

    Elle

    Notch mountains = convex (v-shaped)
    Clip valleys = concave (slit)

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