Friday 29 September 2017

Taming Seam Allowances - a Tutorial

- This tutorial is part of Finishalong Tutorial Week. The full list of this week's tutorials can be found in the Finishalong Quarter 3 Linkup post. -

A full list of my tutorials can be found on my Tutorials page.

Simple quilts have them and complicated quilts have them.
Quilts from solid fabrics and quilts from printed material have them.
Quilts with straight pieces and quilts with curved pieces have them.
The only quilts to have none (or almost none) are wholecloth quilts, or appliqué quilts.

I am talking about seams and seam allowances, of course!
And since patchwork quilts tend to have a lot of those, I thought I show you here how I use the seam allowances to help fit pieces together, and to avoid creating big lumps where a lot of seams come together.

Pressing is our friend

To fit patchwork together accurately, pressing the seams well is almost as important as keeping a scant 1/4" seam allowance.
Take care to not distort your patches while pressing. Especially when your fabric is cut on the bias (often when working with triangles) distortion is really very easy. Exception to this: when you need your fabric to be distorted to make your piece fit better. This may happen where pieces don't quite fit perfectly, for example in improv piecing. See "Ironing Out Inaccuracy" on my Tutorials tab for that.

Seam allowances pressed open

Machine stitched seams can be pressed open (not a good idea with hand stitched seams). This can be the preferred way in some cases, and is perfectly acceptable.

Open the seam allowances at the back, and finger press:

Turn the pieces over, and press the patchwork pieces firmly apart with your iron, making sure that the seam allowances are still open on the back. Pressing from the front this way prevents any pleats at the seam:

Seam allowances pressed to one side

This is my preferred method!
Traditionally, seam allowances in patchwork are pressed to one side. They have to be pressed to one side when the seams are hand sewn, and when you want to quilt "in the ditch" for structural reasons.
Pressing your seam allowances to one side can also be helpful to "lock" seams in place when sewing cross seams, which is why I usually do this.

After sewing two pieces together press the seam flat while the patches are still facing each other. This "settles" the stitches and makes the seam straighter and flatter:

right how it comes off the sewing machine, left pressed flat and "settled"
Next, open the patches and press, keeping the seam allowances flat on the ironing board and they will both be behind the top patch. Make sure to open the patches fully at the seam, you can be quite firm!

the seam allowances will be pressed to the side of the top fabric

seam opened out and pressed

seam allowances pressed to one side

Cross seams

Patchwork consisting of squares and/or rectangles comes in many patterns and styles. But as far as seam allowances are concerned they are all the same, really. They have seam allowances running vertically and horizontally, crossing at the corners of the patches.
Pressing your seam allowances to opposite sides help align the cross seams, like here for a four square block:

seam allowances towards opposite sides

seam allowances "lock" the crossing seams in place

arrows indicate the direction of the seams

Now we make the seam allowances "spin", which means that the directions of the seam allowances go round in a circle:

Stitches at the "crossing" seem to prevent the centre to lie flat, but if we tug at the seam allowances a little, these stitches come undone. Don't worry, your patchwork is not coming apart!

Pull the seam allowances apart at the centre until they lie flat, then give them a good press. In the centre of the four square block a miniature block appears:

And your block is flat as can be:

Multiple cross seams

When we are joining strips of more squares (or rectangles) we can do the same thing, but we have to alternate the directions of the seam allowances:

top row: seams left - right - left - right... bottom row: seams right - left - right - left...
To make our seam allowances "spin" we make sure the directions of the seam allowances are going in a circle around each "crossing" or "corner":

Half square triangles

How I press the seams of half square triangles (HSTs) depends on how they are used.

When HSTs are used with plain squares I prefer to open the diagonal seam on the HST unit to avoid unnecessary bulk:

pressing the units flat

open out the seam

"dog ears" can now be trimmed
The resulting HST unit can now be treated as a square, and when it is used in further patchwork the new seams will be pressed as for squares. You will get open and to-one-side seams in one project.

Windmill block

However, when HSTs are used in a windmill block, we can really make some seams spin:

four HST units to make a windmill block

directions of the seam allowances in the HST units
 When joining two HST units, the diagonal seams will lock and prevent shifting while sewing:

Two pairs of HST units for the windmill block

Direction of the vertical seams (black) follow the direction of the diagonal seams (grey)
When the windmill block is all joined together, the seams should be made to "spin" around. Like before, a little tug is needed to loosen a stitch or two at the cross:

And just like the four square block, we will see our block appear in miniature on the back at the centre:

A very flat windmill block is the result:

I hope you enjoyed this tutorial. More tips and tricks can be found on my Tutorials page.

Remember to link up your finishes at the Finishalong Quarter 3 linkup if you haven't done so yet.

Want to join in with the Finishalong, but don't know where to start? Have a look at the Finishalong page, and join us when Quarter 4 starts on the 1st of October.



  1. Great tips Sandra! Thanks for the tutorial. I didn't know that you shouldn't press hand stitched seams open. You live and learn.

  2. Very helpful, and thanks for the wonderful pictures to clarify everything. I guess from here out it will just be laziness on my part that sees these things not done nicely.

  3. Great Tutorial on the spinning seams! Thanks

  4. Wow Sandra, fantastic tutorial. I wish I had this when I first started quilting. Great job!

  5. great tips Sandra. I didn't know about ripping back those few stitches to help a 4 block sit flat, and I didn't consistently press on the right side. As for the spinning windmills, I will try to remember but my head is spinning!


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