Not every 1/4″ is created equal. Do you know whether you are stitching an accurate 1/4″ seam on your sewing machine? While working on this tutorial I discovered that I haven’t been, so it’s a good thing I started writing this before I make too many more quilts.
Now before you get too incredulous (or embarrassed for not having checked yourself), in my defense I recently purchased a new piecing foot, and admittedly didn’t take too much time to check the seam allowance. Any time you bring a new tool into your studio, you should take a few minutes to make sure you don’t have to make any adjustments to your practice. Patchwork is sometimes to be in a constant state of experimentation: every new variable changes what I think I know. So when’s the last time you checked your 1/4″ seam? Here’s how I checked mine.
Use Accurate Cutting Tools
As you probably know, I prefer die cutting over any other cutting method. This gives me the best accuracy for cutting out my piecing units.
However, if I only need a couple of pieces, like for this test, I will rotary cut units. For this task, I prefer rulers with thin lines and lots of alignment marks. If the lines on the rulers are too thick, it can lead you to cutting units that are too large or too small, which can throw off your piecing.
Regardless of the rulers you have, it’s a good idea to stick with the same brand rulers for your basic rulers. Sometimes with specialty rulers you don’t have much choice, but your basic square & rectangle rulers should be the same. That way, if you’re cutting is off due to the ruler marks, at least you’re consistent.
Use the Right Needle and Thread
My preferred needle is a 75/11 Schmetz quilting needle with 50wt 100% cotton Aurifil thread. If you prefer a topstitch needle, I believe those only come in size 80/12 for this weight thread. Regardless, you’re trying to find a consistent combination that helps you achieve accuracy in your piecing. Whichever combination you choose, keep it consistent throughout your piecing.
Use the Right Foot
If your machine is anything like mine, there are probably 5 or 6 feet that you could use to achieve a 1/4″ seam allowance. The key is finding the right foot for you, that you will use on a regular basis.
Viking recently released a new adjustable 1/4″ foot with guide that allows you to adjust the needle position. I really like this foot for a couple of reasons: one, the metal guide on the right helps me have a visual and physical guide to keep the fabric feeding straight, and the larger hole allows you to move the needle a couple of positions to really tweak the seam allowance.
Test the Seam Allowance
To test your seam allowance, cut (3) strips 1-1/2″ wide by 6-1/2″ long. You may want to cut several sets in case you need to make adjustments to your seam allowance.
At your machine, set up for what you believe is your 1/4″ seam allowance. On my machine, I used the 1/4″ adjustable piecing foot with the needle in the center position.
Take two of your strips laid right sides together, and stitch a straight seam.
Using a ruler with thin lines, align the edge of the ruler with the fabric edge, and observe where your seam line falls. I was actually surprised at mine!
Notice how the seam line is to the left of the 1/4″ line on the ruler? That means when I use this foot, the center needle position is actually a generous 1/4″ seam allowance.
Where did your line fall?
Without making any changes to your setup, press the unit flat. Use a dry iron to press the seams to one side and make sure you are pressing and not ironing.
With right sides together, sew the third strip to your pieced unit, and press the seams to one side.
Here’ you want to make a couple of observations.
First, the strip in the middle should measure exactly 1″:
In this photo, you can see how the center strip is a bit too narrow, and the turquoise is taking up space where the navy strip should be. The second place to check is to measure the width of the full strip set, which should be 3-1/2″:
Notice how this strip set is not quite 3-1/2″. This demonstrates for me pretty clearly that the center needle position with this foot is not the one I want to use.
How to Adjust the Seam Allowance
Seam Line Matches the 1/4″ Line
If your seam line is directly underneath the 1/4″ line and your strip set measures 3-1/2″, then you’ve found your accurate 1/4″ seam and you don’t need to make any adjustments. Yay!
Seam Line is Left of the 1/4″ Line
If your seam line is to the left of the 1/4″ line, your seam allowance is too wide, so you need to move your needle to the right. If your machine doesn’t allow you to move your needle, you may need to mark your machine bed, try a different foot, or use a seam guide that attaches to your machine to accommodate the difference.
In my case, I adjusted my needle one position to the right (shown here as 0.3mm position) and stitched another sample:
When I measured this seam allowance, it was right on the 1/4″ mark on the ruler:
To double-check, I need to add the third strip and observe the next two measurements. You can see in the photo below that my center strip measures 1″:
And if I measure the entire unit, it’s exactly 3-1/2″. Yay!
Seam Line is Right of the 1/4″ Line
If your seam line is to the right of the 1/4″ line, your seam allowance is too narrow. Another way to look at this measurement though, is to note that this narrower 1/4″ seam is the magical seam known as a scant 1/4″!
On my machine, since the center position is a generous 1/4″, and a 0.3mm needle position is exactly 1/4″, the scant 1/4″ must be the next position to the right. Here, I moved my needle to 0.5mm:
After stitching two strips together, and measuring on the ruler, you can see the seam line is now to the right of the 1/4″ line.
When I stitched the three units together and pressed, you can see the center strip is wider than it’s supposed to be:
And the entire strip set is wider than 3-1/2″:
If you weren’t purposely trying to sew a scant 1/4″ seam, this would further validate that your seam allowance is too narrow, so you need to move your needle to the left, or use other accommodations as above.
When to Use Scant vs. Exact 1/4″ Seam Allowance
The way I look at patchwork piecing, I tend to use one or the other just depending on what type of shape I’m sewing together. If I’m dealing with squares and rectangles, that’s pretty easy. I’m going to have the best success using an exact 1/4″ seam allowance.
For other shapes like triangles, hexagons, chisels, or basically any shape with an angle, I use a scant 1/4″ seam allowance. The reason I do this is because I know these shapes have had their measurements rounded (and not always rounded UP) in order to make them easier to cut on rulers with only 1/8″ markings. If I sew with a scant allowance, I can account for the rounding a bit more.
Once you get used to the tools you’re using, you’ll learn where you need to make adjustments in your piecing. The more you practice accuracy, the more confident you will become in conquering some of the more complex blocks.
I definitely learned a lot when working on this tutorial, and I think it just shows that it’s never too late in your sewing career to check your 1/4″ seam! I hope you’ll take the time to do this and may it help you improve your piecing too!