Why Clipping Your Seam Allowance Is Important ~ Part 2: Concave Curves.

When we’re sewing, it can be easy to be impatient to get the project finished.  To have that new top ready to wear or to get your latest soft toy pattern purchase made up and ready for play.  But there are some basic principles with sewing that need to be followed so we end up with a project we are proud to show off.  Clipping curves is one of those jobs that can be easily over looked or rushed, but it really shouldn’t be. Let’s see why.

First, lets look at the two styles of curves … Concave and Convex.

Concave curves dip ‘down’, think of a pot-hole that ‘caves’ in.Concave-curve-paper

Convex curves curve up.

Convex curve - paper

Now lets have a look at why it’s important to clip these curves, starting with the concave curve.

I clipped the paper curve and coloured each alternate section so you can see how each piece spreads apart.  If I tried to fold this over with out clipping it the paper would have torn.


OK, now lets try this with fabric …

Concave-fabricFirst, lets look at this turned without being clipped.


Because of the shape of this concave curve it was possible to turn it without clipping and the puckering is not that obvious.  You could be forgiven for deciding don’t to clip.  But lets have a look at why the seam isn’t sitting flat, then we will have a look at how this looks once we clip it.


The seam allowance itself doesn’t look to bad here, but notice how the fabric on the bottom is rippling.  This is because there is no give in the seam allowance.


Now the seam allowance is spreading apart, just like it did in the paper sample, plus the fabric on  the bottom is now laying flat.  Now lets have a look at the right side.


I have not pressed this at all, but  it is laying nice and smooth … a much nicer result.

To demonstrate this more dramatically, lets have a look at a more acute concave curve.  For this example I have chosen to use the pattern piece from my Ciel Seal pattern.  The back flippers have a tight curve right in the middle. 

Concave-acute-curve-patternAnd now, that same concave curve in fabric …


To see what happens when we turn this without clipping, let’s first take a peak at what’s happening to the seam allowance.


Hmmm … not the pretties seam allowance now is it.  It’s being stretched tight around that very tight curve and causing the fabric to pucker quite badly.  Now  let’s have a look at just how bad this looks from the right side.


Yep … not pretty, you definitely would not want this on your finished project.  So lets move on quickly to clipping.

Concave-acute-fabric-clipped-insideFirst, the inside,  again the seam allowance is spreading, but this time the distance between each section is bigger than they were in our first example.


In the images to the right, I have clipped the tightest section of the curve three times.  In the image below you can see that although there is a big improvement, it’s still not as smooth as it should be.

In the images to the left, I have clipped several times close together at the highest and tightest part of the curve and down each side.  Again, I haven’t  pressed this curve and yet it is nice an smooth and a much nicer result.

So there we have it, taking the time to clip your concave curves is time well spent and makes your finished projects look great.

In part 3, we will look at why it’s good to clip you Convex curves.

Click here for part 1.

Happy sewing … signiture





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