Sewing Tips | 5 Tips for Achieving an Accurate, Consistent Seam Allowance

 Stephanie Palmer, the Late Night Quilter, is a professional longarm quilter and pattern designer. Stephanie is the creator of The Quilter’s Planner 2016, a new day-planner filled with project planning tools, to do lists, goal setting, graph paper, free motion quilting space and patterns from top designers. Now you can finally keep track of your whole life in one space! The Quilter’s Planner is now available for pre-order. To celebrate, Stephanie is hosting a fat quarter bundle giveaway on her website this week. Hop over to Late Night Quilter and enter to win!

Stephanie is here with 5 Tips for Achieving an Accurate, Consistent Seam Allowance. She shows us her favorite tools, discusses important considerations for your sewing machine and Stephanie even has a video showing her favorite seam gauge/seam guide combination in action!

As a sewist, obtaining an accurate seam allowance is one of the most important things you can achieve. The exact size of your seam allowance does not necessarily make a difference if you are sewing simple patchwork, sewing consistent seams across an entire quilt top. However, an accurate ¼” seam is essential for intricate piecing, points and group projects like bees and charity quilts.

What about a Scant Quarter Inch Seam Allowance? These days many quilters talk about sewing with a scant ¼”. This means sewing a seam that is approximately 1-2 thread widths less than an actual ¼”. When you sew, a tiny bit of fabric is folded over the thread during pressing, which makes your finished seam slightly larger than you may have anticipated.

A scant ¼” seam is most important when you need to be mindful of maintaining points in your finished quilt. If you prefer not to sew with a scant ¼” seam allowance, read below for information on modifications in pressing and thread choice that you can make that will help you achieve the same effect.

5 Tips for Achieving an Accurate, Consistent Seam Allowance

Tip #1 – Choose a Seam Guide:
My first quilting instructor encouraged me to eyeball the ¼” seam because every good quilter knows exactly what ¼” looks like. In other words, seam guides are for cheaters. I wish I realized then how wrong this was! There are many wonderful choices for a seam guide. And there is NO SHAME in using one. Each choice comes with its own pros and cons, which you can read about below.

Here are some of the most common seam guides:

Magnetic Guide: 
This affordable tool magnetically secures to the metal throat plate of a sewing machine. It is secure and can be adjusted to accommodate any seam allowance. However, it is advisable to keep strong magnets away from computerized sewing machines; they can interrupt communication between circuits and cause computerized machines to become inoperable.

Screw-in Guide (comes with certain sewing machines):
Your machine must have pre-drilled holes in the throat plate to use a screw-in guide like the one shown. It is an excellent choice for several reasons: it is more secure than any sticky guide; it can be adjusted to accommodate many seam allowances; it protrudes in front of the foot further than the guide bar of a ¼” foot; and finally, it cannot be bent out of shape like the guide bar on a ¼” foot can. (Scroll to the bottom to see a video featuring a screw-in guide).

A Quarter Inch Foot: 
Many sewing machines come with a ¼” foot, and if you have a machine that does not, check with your manufacturer. There is some variability in the accuracy of a ¼” foot. The guide bar tends to be rather flexible, which can lead to small, but significant inconsistencies in seams. If you use a ¼” foot, I recommend testing the accuracy of your seam allowance before each project, and several times as you work to re-assess the reliability of the tool.

Moleskin Foam:
This foam is made to protect and pad human feet, and can be bought in any grocery store or pharmacy. It comes in a small square, with 2-3 sheets per package, it can be cut into strips with a rotary cutter. Stick three layers to the base of the machine to create a quick and effective seam guide. This creates a more significant ridge than the masking tape. This guide is temporary, and will eventually lose its stickiness. It may leave some sticky residue on your machine that can be washed away.

Layers of Washi or Masking Tape:
Colorful washi tape, masking tape, or painter’s tape can be layered to create an effective, easily changeable seam guide. I recommend 20 layers to create an effective ridge that will guide the fabric. However, some people may prefer not to bother creating a ridge for the fabric, instead relying on the visual cue the tape provides. This temporary seam guide can also be easily adapted to assist you in sewing Half Square Triangle units without marking. Although it is easy, the tape does shift and lose its stickiness over time.

Sticky Notes: 
This is the quickest and easiest method, and perfect for getting going on testing the accuracy of your seam allowance today. However, a pile of sticky notes shifts easily, and you need to carefully monitor your accuracy if you choose this method.

Ideal Seam Guide by Sew Very Smooth: 
This is a ruler with a sticky rubber backing that adheres on the base of your sewing machine, to the right of the needle. This is repositionable, and lint can be cleaned off of it, however it does shift more easily than the screw in guide or a ¼” foot. It works well on featherweights. The rubber can be replaced when it wears out, and it can accommodate a walking foot.

Moving the Needle on Your Machine to the Left or Right: 
This is another easy solution, but take care! When you turn off your machine, it may return to default settings. Leave yourself a note to remember to reset it before you begin sewing again.

Tip #2 – Consider How You Press (open or to the side) 
How you choose to press your seams affects the finished allowance. Pressing open leads to a more accurate allowance. But if you plan to send your quilt to a longarmer, or you envision some stitching in the ditch in your quilt’s future, then pressing seams to the side is advised. Regardless, it is always wise to double check and adjust your seam allowance with the materials and pressing methods you plan to use in your project.

Tip #3 – Consider Thickness of Thread 
The thread you are using to piece is eventually folded into the seam allowance when you press seams to the side. So consider using a finer weight thread (60 wt.) to sew seams.

Tip #4 – Use a Straight Stitch Sewing Machine or Needle Plate
A straight stitch machine or a single stitch needle plate actually improves the accuracy of your seam allowances! Many who have made the switch to a straight stitch machine or plate can vouch for the improvement in accuracy (myself included). The hypothesis is, with machines that are capable of a variety of stitches (i.e. zip zag stitches), there is more wiggle room for the needle to shift ever so slightly. A Straight Stitch Needle Plate can make stitches straighter and more aligned, with less shifting of fabric.

Tip #5 – Check your Seam Allowance

Ideal Seam Gauge: I love this particular tool because it has 10 options for measuring seam allowances, including a 1/8″, scant ¼”, a true ¼” and a 3/8″ allowance, among others. However this tool is pricey, at $20.

Old Fashioned Ruler Test: If you prefer not to buy an extra gadget, you can just place a ruler under your presser foot right on the ¼” mark, gently lower the needle, and then place the seam guide of your choice.

Perfect Piecer, By Jinny Beyer: (This is excellent for curves, or if your ¼” seam allowance tends to start off just right, and then tends to drift as you sew the seam!) With this tool, you can carefully mark dots that are precisely ¼” away from the edge of the fabric. Here’s a link to Jinny’s video showing how she uses her tool.

Sewing Test: Carefully cut three 1 ½” wide rectangles. Double check to make sure you have cut them accurately. Sew the three pieces together (along the longer seam) using your seam guide of choice. After sewing, the center strip of fabric should measure exactly 1″ wide. The piece as a whole should measure 3.5″ wide.

Index Card Test: My friend and mentor Mandy Leins wrote about her method for easily switching back and forth between two sewing machines, and checking to confirm the seam allowance is the same between the two.

My Favorite Seam Gauge/Seam Guide Combination:
My favorite combination of all of these previously mentioned tools and techniques is to use a straight stitch machine (I sew on a Janome 1600P), along with the Ideal Seam Gauge and the Screw-In Guide that came with the machine. Since I switched to these methods, my quilts lay flatter and fit together more precisely, and I shed a lot fewer tears! Here is a quick video showing my favorite combination in action.