Tips & Tricks | Sewing Smooth Curves Every Time

In home décor sewing, there are lots of squares and rectangles. Pillows, placemats, curtain panels... nice flat shapes with plenty of good ol' right angles. But, if life didn't throw us a few curves now and then, it wouldn't be a very interesting journey would it?! You may feel a little apprehensive about learning to sew curves, thinking you’re happy with all things square. But learning to bend those right angles is a necessary part of sewing, and opens up new, fun possibilities. With our help, it's easy to do too! 

First things first: vocabulary building. An inward curve is a concave curve. And outward curve is a convex curve. The key to sewing them successfully is accurate seam allowance, proper clipping, and careful pressing. The main difference between inward and outward curves is how you clip them. Clipping the excess around a curve eliminates the bulk and creates a smooth outer edge while maintaining the curved shape.

In garment sewing, the curve around a neckline is an inward curve. If you measure the length of the seam compared to the length of the curve, you'll discover the seam is longer. Therefore, you need to clip into the seam allowance so when it’s turned right side out, the fabric will spread and allow the inward curve to take shape. Whereas, the curve along a princess seam through the bustline is an outward curve. If you measure the length of the seam compared to the length of the curve, you will discover the curve is longer. Therefore you need to clip notches of excess fabric from the seam allowance so when it’s turned right side out, the fabric won't bunch up along the outward curve's pretty shape. I know, I know... you're wishing you'd stayed awake in Mr. Harrison's geometry class!

We've used our fair share of inward and outward curves here in the Sew4Home studios, where we make all kinds of shaped items. 

And these pretty Heart Sachets and sweet Stuffed Owls show off some inward curves.  

Inward curves

First, a little bit about cutting curved pattern pieces (this relates to all curves, not just the inward variety). Using sharp fabric scissors is important in all fabric cutting, but it's especially critical on curves. You want to clip with just the tip of the scissor around the curve. Cut slowly and evenly to keep the shape of the piece accurate. Sometimes, a curve can be difficult to keep even because of your position as you cut and/or the size of the curve. If this is the case, cut the curve half way from one direction, then change your position, and cut the second half from the opposite direction. Another option is to use a rotary cutter instead of scissors.

Once you have your curve-shaped project ready to go, it's time for sewing.

1. Set up your sewing machine for a straight stitch.
2. Determine your seam allowance. In our example, we’re using ½".
3. Place your fabric, right sides together, under the presser foot.
4. Because maintaining a consistent seam allowance is so crucial, we recommend marking the curve, especially if you’re a beginner.
   
5. Knowing the appropriate marking on your needle plate is equally important. You need to know where to look as you’re guiding your fabric through the machine. For curves, you want to keep your eye on the seam at the exact measurementin line with the needle, not before the needle (which is where we tend to look when sewing a straight seam).
   
   NOTE: We’re lucky to have Janome as one of our sponsors, and we get to use their great machines every day. Several of the Janome models in our studios, like our Horizon Memory Craft 15000, have a built-in cloth (or seam) guide (shown in the photo below), which makes it super easy to maintain an even seam allowance. This may also be an option for you, depending on the type of machine you have and its available accessories. We recommend visiting your sewing machine dealer for more information. In addition, many sewing machine owners have fashioned their own homemade guides, using household items, such as rubber bands, post it notes, and masking tape.
   
6. Remember, anytime you want to be accurate, it’s best to take it slow and easy. This is tip-top advice for sewing curves. As you sew your seam, you are angling the fabric slightly to the right, depending on the degree of the curve, to maintain the seam allowance at the needle.
   
7. When the seam is finished, you're not finished. You need to clip the curve. 
8. If the seam allowance is not clipped at all, when the fabric is turned right side out, this is what the seam looks like. Yikes!
   
9. Clip into the seam allowance every ½" - ¾" along the curve, being very careful to not clip into your seam.
   NOTE: A quick note about scissors. For this technique, and many other sewing techniques, it’s a good idea to own a small pair of sharp scissors – perfect for this kind of job!
   
10. As an alternative, you can clip each side of the seam allowance at opposite angles to one another. In other words, don't cut through both sides of the seam allowances at the same time; cut each one independently.
    
11. Press well (following our instructions below), and your inward curve should now look nice and smooth, like this:
    

Outward curves

1. Following the same steps for sewing inward curves, prepare your project's fabric pieces, mark the seam allowance, and set up your sewing machine for a straight stitch.
   
2. Sew along the outward curve, remembering, as above, to strictly maintain the seam allowance. In order to keep on track, depending on the shape of the curve, you may need to stop with the needle down, rotate the fabric ever so slightly, then continue sewing.
   
3. Before doing any clipping, turn the curve right side out, then immediately turn it back wrong side out. You'll be able to see where the fabric was bunching up along the seam when right side out. This is how you know where you need to clip.
   
4. Conversely to inward curves, you do not clip into the seam allowance on outward curves. Instead, you create "V" shaped notches in the seam allowance to remove bulk approximately every ½".
   
5. As above, you can also choose to clip each side of the seam allowance separately so the notches are opposite one other. This gives a smoother finish, and is particularly smart if you're working with a heavier weight fabric.
   
6. Follow the pressing instructions below, your outward curve should now look like this:
   

What about full circles?

A full circle is sewn with the same precision and notching technique as an outward curve. We recommend notching the sides of seam allowance independently and opposite of one another as shown above. This will help keep the fabric as smooth and even as possible along the entire circumference.  

NOTE: If you have a sewing machine with a Knee Lift feature and a programmable Needle Up/Down function, (two additional can't-live-without features ofnour Janome studio machines), we recommend using these in combination. They enable you to keep your hands on your fabric as you sew around curves. The needle stops in the down position and you use your knee to lift the presser foot slightly so you can rotate around the curve a little at a time, holding on to your fabric with both hands the entire time. 

What about sewing an inward curve to an outward curve?

You also run into this circumstance all the time in garment sewing when you sew a set-in sleeve into a garment. The top of the sleeve is an outward curve, while the arms-eye (the hole where your arm goes through) is an inward curve.  

To help make the two fit, you run basting stitches in the seam allowance of each to help gather up the excess slightly so you can fit the curves inside one another. 

When the pieces are placed right sides together, it helps to sew with the outward curve piece (in this example, the sleeve) against the feed dogs of your sewing machine with the inward curve piece (in this example the bodice portion of the garment) on top. The feed dogs can then help ease the excess around the curve of the sleeve into the garment, creating a nice, smooth fit.

You'll also sometimes see inward and outward curves joined in quilting. Since ¼" seams are traditionally used in quilting, there is not enough excess to clip. Instead, it's recommended you sew the curves from the center out in either direction.

The importance of pressing

Pressing is a vital component of smooth curves. After the clipping process, place your sewn pieces over a pressing ham, right side down. With an iron set to the appropriate temperature for your fabric type, press the seam open. The curve of the ham will help keep the shape of the curve as you press. Pressing the seam open first, before turning right side out, will bring the sewn edges together flat. This way you will not have any “dents” in your seam where the fabric didn’t turn out completely. 

NOTE: This works on straight edges too!