Getting an accurate 1/4″ seam

If you’ve ever done a jigsaw puzzle that has warped pieces, you know how frustrating it can be when pieces don’t quite fit together. This can easily happen to a quilt if you’re not careful. The more accurately you cut and sew, the easier things will go together and happier with the process you’ll be. If you need to cut a 4 1/2” square, you can’t cut 4 3/4” and say “close enough”. Just like carpenters – measure twice, cut once.

If your fabric is cut accurately, that is half the battle. The other half is sewing accurately. Quilting uses a 1/4” seam allowance. (Seam allowances is the edge of the fabric that goes to the inside.) 

If you sew with a 3/8” seam allowance, all your pieces will be too small, and they won’t line up. If you sew with an inconsistent seam allowance, you will be really frustrated. Take the time to practice and find your accurate 1/4” seam allowance. It is worth it in the long run.

Most sewing machines have a 1/4” line on the plate and many even have 1/4” feet, but don’t assume these are accurate. The weight of the fabric, thread and needle can all impact the size of seam you need.

Here’s the big secret to having an accurate 1/4” seam allowance:

Don’t measure the seam allowance!

What really matters is the size of the fabric left in the piece. 

You will always lose a tiny bit in the fold of the fabric. That doesn’t really matter.

Use this technique to test how big your seam allowance should be. Don’t worry about measuring it because we are talking about differences of less than 1/8”. Just find the spot and mark it on your sewing machine bed.

1. Cut

Cut a few 3″ squares out of scraps. It is important that they are exactly 3″ square. 

2. Measure

At your sewing machine, put a post-it note on the 1/4” seam line. If your machine doesn’t have one, use a ruler to measure it.

3. Stitch

Take two squares and sew the seam, aligning the edge of the fabric with the post-it. Press as you normally would.

4. Measure

Measure the pieces. Each piece should be 2 3/4″ wide.

5. Adjust if necessary

If they are less than that, you need to slide the post-it slightly toward the needle. If they more than that, move the post-it slightly away from the needle.

Once you’ve adjusted the post-it, try again until you end up with two pieces 2 3/4″ wide.

6. Repeat

When that is done and accurate, try adding another square onto the piece. With a proper seam allowance, you should end up with a 2 1/2″ piece in the middle.

When you’ve don’t that, you can be confident that is the place on your machine to line up your pieces. Put some masking tape at the spot to remember it, and use it to align as you sew.

Every once in a while, especially if you’re switching to a different kind of fabric or needle, you will need to check again, but it gets easier and faster every time you check it.

Sometimes you can’t use a mark on the bed of your machine (like the most popular method of making half-square triangles). In this situation, you need another option such as:

• If your needle can move, you can move that so that the right seam allowance lines up with the edge of the presser foot. 

When you do this, be sure to make a note of the settings so that you can go back to it when restarting the machine.

• Use a laser line to guide your stitching. This could be worth the investment if you have a lot of pieces to do.

Every once in a while, you will need to check again, especially if you’re switching to a different kind of fabric or needle. It gets easier and faster every time you check it.

Taking the time up front will save time in the long run.

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