Saturday, September 6, 2014

What is the deal with the "scant 1/4 inch seam"??

If you are new to quilting, you might have found yourself asking,

"Why do I need to sew with a scant 1/4" seam?"
"What on earth do they mean by 'scant'?"

Today's post is to clear that up for you. 

Long ago, there was a counsel of quilting wizardesses who met to decide what size was the perfect seam size for piecing quilt tops... Ok, not really. But the whole WHY behind the 1/4" seam allowance is not very scientific. It has just become consensus over the years (from what I've learned) that 1/4" is:
  • Enough of a seam allowance to provide stability and to keep your seams from pulling apart over time
  • Not too much fabric to make seams bulky when quilting your three layers together
  • Not too much fabric to end up hidden behind your finished quilt (we want to show off the fabric in our quilts!)
So, if you have ever made a quilt from a pattern, or ever drafted your own quilt pattern, you know that your seam allowance is important when calculating your yardage requirements. When you are learning piecing, you will see that if you are joining multiple rows, columns, or blocks together to get a finished quilt top, your finished quilt size depends GREATLY on your ability to sew the seam allowances accurately. The more seams there are, the more an error in seam allowance will affect the finished product.

Here is an example from the quilt I'm currently piecing:

I was sewing 2 1/2" strips in strip sets, so there were seams on both sides of each strip. If you subtract 1/4" for each seam allowance, the finished strips should be 2 inches wide. I hadn't pieced a quilt top since my last sewing class at my LQS (Local Quilt Shop) and had changed presser feet on my machine since then. With my other quilts, I knew that my scant 1/4" seam was done by moving my needle position to the far right and aligning the edge of my fabric with the edge of my presser foot. 

So, what's the problem? My new presser foot, a walking foot, was WIDER than my other one. So, all of my seams were just a tad wider than 1/4".

This is a picture of 9 strips, which should have come to 18" wide after sewing and pressing.
Each solid line on my ruler is one inch. See how the first few strips from left to right are very close to hitting the 2-inch width? As you go further to the right, the differences add up and the whole set ends up being short by over 1/8 of an inch:

Here's a closer look. More than an eighth of an inch shy of where my strips should have ended.

Sure, it's not that big of a deal, but I want my quilt to come out to the proper finished size since I am making it for my mom's king size bed. She gave me measurements of her mattress and I want the quilt to fit perfectly to her specifications.

Now would be a good time to show you what "scant" means, in this sense. When you are playing around with your machine to find your perfect seam guide, make sure you take your pieces and press the seams open or to one side and measure the finished fabric width. You wouldn't guess, at least I never thought of it when I was learning, that even the width of the thread and the fold of the fabric after pressing a seam takes a fraction of width away from the finished dimension.

To correct for this phenomenon, you should experiment with your machine, your thread, and your pressing to find what truly gives you that finished dimension you're looking for. Here is a picture of what works for me:

With my ruler lined up on the right edge of the fabric, my "scant" 1/4-inch seam measures just to the inside of the 1/4-inch line on my ruler. After pressing, this leaves me with exactly 1/4-inch less fabric showing on the finished piece.

So, after going back to my machine, I did a few test seams on paper and on scrap fabric until I was sure of my NEW setup for a scant 1/4" seam using my walking foot. (I will do another post on "walking foot" versus "regular presser foot" later, so if you're confused, stick around for that one.) With my walking foot, if I have my needle to the far right, I needed to line my fabric up just a smidge to the left of the right edge of my presser foot.

I made this picture extra large so you can see what I mean. My walking foot has two cut-outs, or "tracks" for the upper feed dogs. Do you see the feed dog I circled in blue? There is a matching one on the other side of the needle. Now look at the lowest piece of metal touching the top fabric (that's the foot) and do you see the two rectangular cut-outs? So the fabric was supposed to be lined up right at the edge of that right rectangular cut-out, shown by yellow arrows.

I gave it a whirl and after the first strip, I noticed an issue with this setup. First of all, it's kind of hard to see that target while I'm sewing. Secondly, because the edges of both fabrics are just barely being caught between the upper and lower feed dogs on that right side, there was some slippage going on.

This could happen anyway, but I think the lower fabric was slipping more because that lower feed dog wasn't grabbing on to enough of the fabric. The fabric was riding the edge. We all know it's not safe to ride the edge. ;)

I put the strip back in my machine to show you. This already has some ripped stitches because I was going to redo it:

Have no fear if these things happen! This is what beginning quilting is all about. Troubleshoot, troubleshoot, troubleshoot. Here is what I tried next.

I changed my needle position from the far right back to the center.

After some testing, I found the new setup with my walking foot. If the needle is in the center, I need to line up the fabric with the INSIDE edge of that right cut-out on my presser foot (yellow arrows). I actually like this better. The pair of feed dogs on the right side aren't even touching my fabric anymore, but that's ok. I actually like them not grabbing the fabric at all rather than grabbing just the very edge and sometimes causing the bottom fabric to shift.

In the picture below, you can see how my top and bottom fabric stayed together better with this method, since the feed dogs were not touching the right edges of my fabric anymore.

 And I still got that purty scant 1/4-inch seam.

After pressing, you can see how my 2 1/2 inch strip measured exactly at 2 1/4 inches, as planned. 

Thanks for hanging in there with me through a long post. I hope this helped you figure out different ways to experiment with your own machine and find your perfect scant 1/4" seam. 

No comments:

Post a Comment