PM/GC Quilts Skill Builder Series: Part 4 – Quarter Inch Seams

Once again, Jeanne and I are discussing different aspects of quilting. She will address preparation of fabric before sewing, including washing vs. not washing, pressing, finding the straight of grain, and the importance of straight of grain and bias.  Meanwhile, I’ll focus on achieving consistent seams.

Quarter inch seams can be one of the most frustrating parts of quilting. Here’s a little secret, though – a quarter inch doesn’t always matter. If you are the only person working on the project, it doesn’t matter if your seams are exactly 1/4″, as long as they are consistent. A block sewn with consistent seams will finish with accurate seam intersections and points. It may be slightly smaller or slightly larger than the quoted block size, but it will still be accurate. If you assemble the blocks into a top with consistent seams, even using pieced borders, everything will align properly.

(Whoops! As Lisa of Misadventures in Quilting noted, this is not entirely true! While it is true that consistent seams are more important than 1/4″ seams in some blocks, more complex blocks do depend on a 1/4″ seam allowance for all of the parts to go together correctly. So you can make a quilt of identical components (for example, all squares, or all half square triangles, etc.) and the measurement is not as critical as the consistency, but if you combine those components in a single block or quilt, the 1/4″ seam is essential. Thanks, Lisa!)

So why are we so hung up on the perfect quarter inch seam? Well, because we often don’t work on projects alone. Bee blocks, group  quilts, round robins and signature quilts – when more than one person works on a project, their seams must also be consistent between each other. If one person is consistently sewing their seams 1/16″ larger than the other(s), their blocks will not fit into the rest of the quilt. There are ways of getting around this problem with sashing, frames and setting options, but that’s something we’ll talk about later in the series.

Also, although consistency is more important than 1/4″, you still need to learn how to be consistent. And if you’re working on that, well, you might as well work on getting your seams to be consistently 1/4″. That way, when you work from patterns your measurements will match those in the pattern.

So how do you achieve a perfect 1/4″ seam?

Cutting

We sometimes overlook the importance of accurate cutting as it impacts our seams. When you think about it, though, if your pieces are cut slightly smaller than they should be, of course you’re going to end up with a smaller block. Look at the markings on your ruler. Some rulers have wider markings than others. Here you can see the blue fabric is measured to the outside of the 2 1/2″ mark, while the pink fabric is measured to the inside of the 2 1/2″ mark. (Click on the photo to see it larger.)

When you cut, aim for the outside of the mark (like the blue fabric) rather than the inside.

Sewing

After sewing the seam, you fold the fabric back and press. That fold can have a minuscule affect on the size of the finished piece, but when you add hundreds of seams together, all of those “minuscules” add up. As you fold the fabric back, you aren’t folding directly on the seam, but immediately next to it. That one or two thread difference is the reason experienced quilters talk about a “scant quarter inch seam.” So what do we mean by “scant”? The best definition is “less than the full amount, often deliberately so” or, “just barely.” Instead of trying to sew exactly at 1/4″, aim for one or two threads less than 1/4″.

In this photo, the blue fabric is lined up just inside the 1/4″ mark on my seam guide. You can also see that it’s just inside the edge of my quarter inch foot.

In the second photo, the pink fabric is lined up directly on the 1/4″ mark on the seam guide, and it is at the outside edge of the quarter inch foot.

The first example, with the blue fabric, will result in a more accurate seam once the pieces are pressed.

Thread

Thread thickness can also play a part in how much space is taken up when you fold the fabric back. Here are two threads by Aurifil.

The black thread is 50 weight and the green is 40 weight. As I mentioned in the Tools post, the lower the number, the thicker the thread. I prefer to piece with 50 weight thread because it is thinner. It is very difficult to see the difference between the two – it’s easier to tell which is thicker when you touch them. I used the black thread with the blue test pieces, and the green thread with the pink test pieces.

Testing Your Seams
How do you know if your seams are accurate? Using the principles above, cut several pieces of fabric 2 1/2″ x 1 1/2″.

Sew them together along the long edges. Press them and measure the finished piece. It should be exactly 2 1/2″ square.

In the photos you can see that the blue fabric measures exactly 2 1/2″ square. It was cut to the outside of the ruler marking, sewn with a scant 1/4″ seam, and used the thinner thread. The pink fabric was cut to the inside of the marking, sewn at exactly 1/4″ and used the thicker thread. As you can see, the pink square is almost 1/8″ less than 2 1/2″ wide.

Seam Guides

There are a number of tools available to help you maintain accurate seams. Many sewing machines come with a quarter inch foot, and if yours doesn’t have one you may be able to buy one. Some have a little piece of metal extending down from the right side of the foot that serves as a stopper for the fabric. I haven’t had much luck with those, but you might find that kind helpful.

My paper seam guide has worked well for me for several years, although it’s getting rather ratty looking. It is no longer available as a free PDF, but you can purchase a sturdier adhesive version from the creator at Reanna Lily Designs. I especially like this layout, but there are other seam guides available as well. The Angler 2 by Pam Bono Designs is focused more on helping you sew 45 degree angles (like you need for half square triangles and other pieces with that angle), but it also has a quarter inch seam line. Another product is the Fast2Sew Ultimate Seam Guide from C&T Publishing. This has both straight lines in 1/4″ increments as well as angled lines.

With a little ingenuity, you can create your own seam guides. Start with a piece of 1/4″ graph paper or a 1/4″ ruled index card. Trim on one line, being careful to cut EXACTLY at the line to maintain accuracy. I like index cards because they’re not as floppy as paper, but it’s helpful to have a perpendicular line to make sure your guide is straight. Use a ruler to draw a line that forms a perfect T to the preprinted lines.

Place the card or graph paper in your sewing machine, putting your needle through the preprinted line…

…and using the line you drew to make sure the card is straight. I lined mine up with the seam on my machine where the tray flips open. Be sure to line it up on both sides of the card to keep it straight.

There are several ways you can create a guide from this point. The easiest is to just draw a pencil line on the bed of your machine. It washes off easily if you want. I used the card to extend the lines past my seam guide onto the tape and the bed of the machine. (The card looks a little crooked – it slipped when I picked up the camera after I drew the lines.)

But see above there – I also created a seam guide with a little pack of sticky notes. Just lift off a small stack and press it to the bed of your machine against the edge of the card. By using a stack instead of a single note, you have a built up edge to guide your fabric.

Sticky notes are not permanent, which can be good, but they can also be easy to move around or knock off. Another option is blue masking tape, found at the hardware store. Blue tape is made especially to remove easily without leaving a residue. You can place just a single layer as a semi-permanent guide…

…or you can cut through several layers on the roll and peel it off as a thicker piece. Please be very careful when you cut this – it’s easy to injure yourself! Like the sticky notes, it creates an edge to hold your fabric in alignment.

Other Tips

Have you ever noticed that your seams weave back and forth instead of going straight? Part of the problem may be where you’re looking as you sew. Instead of watching the fabric under the needle, watch the edge of the fabric against your foot or your seam guide. By the time it reaches your needle, it’s too late to correct the wobble.

Your sewing machine may allow you to adjust your needle position. If you notice that your seams are always a tiny bit too big or a tiny bit too small (one or the other, not jumping back and forth between the two), try moving your needle just a tick.

My best tip for creating accurate blocks it to sew first, then cut. As demonstrated in the half square triangle posts, cutting larger pieces, sewing, and then trimming to size makes accuracy much easier to attain. It might seem like a little extra work, but if you figure how much time (and frustration) you waste redoing blocks that didn’t turn out quite right, it’s a wash. As you become more familiar with how a block breaks down, you’ll be able to tell when you can cut bigger and then trim, and when you need to make it accurate the first time through.

Do you have any other tricks for accurate seams?

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15 thoughts on “PM/GC Quilts Skill Builder Series: Part 4 – Quarter Inch Seams

  1. I really appreciate the time you and Jeanne are taking to do this. I am fairly new at quilting and sometimes I don’t know enough to know what I should be asking.

  2. This is the most useful thing I have ever read on a quilt blog. This explains why my blocks are sometimes slightly off even though I thought I cut it and sewed it accurately. This will save me many headaches in the future.

    Thanks.

  3. What a helpful post! It has never been explained to me WHY one might strive for scant seams, but now that I know, it makes so much sense! Thanks for helping out the rookies like me :)

  4. Thank you, thank you, thank you. I have such trouble with 1/4″ seams. I will have to try some of the hints you posted.

    I am really enjoying this series. THANK YOU!

  5. I love these tutorials you are doing!! Great work. Now that being said, I hate to disagree with one statement you made, but I think you just simply overlooked one aspect of only sewing with a consistent seam instead of an accurate scant 1/4″ seam. You stated the blocks will all go together as long as you are consistent. Not necessarily so, consider blocks that have a lot of piecing in one section and not as much in others. The sections that have multiple small pieces will shrink or grow with an inaccurate seam allowance making the sections with less or no piecing not fit together properly.
    Hope that made sense, if not email me and I will try to explain myself better.
    Thanks again, really do appreciate your hard work and great tutorials!!!!!!
    Lisa

  6. I have a Janome and I use my quarter inch seam foot. LOVE IT! I have also used moleskin stuck to my machine at 1/4 from the needle, similar to your pad of sticky notes.

  7. Thanks so much for this series. I am excited to read your quarter inch seam hints- I struggle with getting an accurate seam, and look forward to trying them out.

  8. Wonderful hints! I always thought just being consistent would be fine but now I see why it matters. And I’ve also always wondered EXACTLY where to cut the fabric and line up the fabric so thanks for this very helpful post. :-)

  9. I was taught the 1/4 inch moleskin trick and it works great – easy to remove and put back on, and raised so it acts as a guide too.

  10. I use moleskin, too. It is placed on the bobbin cover. I found it was annoying to have to lift it off to do half square triangles and then to have to replace it. To get around that I bought a second bobbin cover – for my Janome it was a couple of dollars. The quarter inch foot for the Janome has a metal edge so I swap the foot and the bobbin cover when I change between half square triangles and regular piecing.

  11. I have been trying for over a year to get accurate blocks, and I could not figure out what I was doing wrong. I have gotten so much better with this quilt a long. These tutorials on 1/4″ seams helped so much! (Didn’t know about the moleskin for ex.,or why consistency wasn’t enough. I’ve been trying so hard to be accurate.) Thank you!

    • Yes, the card is basically just used to line up the tape. Also, the lines on an index card (at least in the US) are exactly 1/4″ apart, so it makes a cheap, easy measuring guide.

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Thank you for sharing your thoughts! I try to reply to every comment, but sometimes it takes a few days. And sometimes, well... it has been known to drop off the radar. I'm easily distracted by shiny things.

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