How to Perfect Your Quarter Inch Seam Allowance - A Quilting Tutorial

To make your ¼ inch seam accurate we must address three basic steps.

Step One: Accurate Cutting with a Rotary Cutter

AKA Preventing the Dreaded “V”s and “WOW”s

Working with the true straight grain of your fabric will make sewing your pieces together easier and more accurate. 

If you straighten an edge using only a single fold or the selvedge edge as your guide then you are more likely than not to get strips that have a “V” or “WOW” in them.

All sub cuts made from the resulting strips will be slightly off grain making them want to twist as you feed them through your sewing machine.  

This will affect your ability to sew a consistent ¼ inch seam.

To prevent this place the fold of your fabric towards the top of your cutting mat.

Fold the selvage edge towards but not all the way to the fold at the top of your fabric.                                         

Measure from fold to fold with your quilting ruler.         

Use an easy measurement to view on your ruler such as anything on the ½” or 1” line.        

                                 

 When you get the same measurement across the length of your fabric then you are “On Grain” and ready to straighten an edge. 

Don’t try to straighten more than  25” to 30” at a time. 

It’s better to re-measure and re-straighten as required. 

Now…use one of the long horizontal lines on your ruler to line up to the bottom fold of your fabric. The other lines should be square to your top fold.

 Trim a little bit of fabric off the side to “straighten an edge.    

                          

If you are right handed you will straighten from the right and cut your strips from the left.

If you are left handed you will straighten from the left and cut your strips from the right.

When cutting your strips be sure that the line you are measuring is ON TOP of the straightened edge.

If your measurement line is on the outside of the cut edge you will “lose” approximately 1/16” to 1/8” of fabric.

It doesn’t seem like much but by the time you have cut eight strips you have “lost” up to an inch in the accuracy of your measurements.

No matter how well we sew if our cutting is out our blocks will still be the wrong size.

*Hot Tip: 

If you square your body to your ruler it won’t slide out of place and you will not need as much pressure to make your cuts. 

This is accomplished by simple physics in that all your weight is automatically transferred down into the table so that your ruler stays in place and your cutting hand has more power without more pressure. 

To be sure that you are square to your ruler stand with your feet flat and side by side and line your “Belly Button” up to the hole in your ruler. 

It’s easy to remember because it will make you laugh…and it works!

Step Two:  Accurate Sewing

I generally use 50 weight cotton thread with a sharp needle when piecing cotton.

Good needle choices include Quilters size 75/11, Jeans Denim size 70/10  or Microtex Sharp size 80/12.

If your fabric is a blend of poly/cotton you may use poly/cotton construction thread.

If quilting with polyester, piece with 50 weight polyester thread.

*Please Note 

Though weight is the most common way that we compare threads it is only accurate when you compare threads within the same category and with the same number of ply.                             

For instance a 50 weight cotton three ply will be thicker than a 50 weight cotton two ply as the thread is 50 weight per ply.                                                    

A cottonized polyester will be different from a filament polyester.                                                        

This subject is covered in depth in my Lecture/Demo 

All About Thread                                                                        

Now for the most confusing part about ¼ Seam Allowances

A measured ¼” is the measurement that is on a ruler.

Most patterns, books etc. will tell you to use a ¼ inch seam allowance to piece your quilt.

It is assumed that quilters know to piece with a “scant” or “quilters” ¼ inch seam allowance.

We sew with “just under” a measured ¼ inch to allow for the width of our thread as well as the fold over of the fabric in our seam allowances.

Most sewing machines can sew a basic scant ¼ seam with the use of a Standard Foot or ¼” Piecing Foot

You may need to adjust your seam allowance according to the thickness of your fabric and the thickness of your thread.

 Pressing your seam allowances open will give you a slightly different measurement than pressing all seam allowances to one side.

Simple designs consisting of pieces that are all the same size can be pieced with a scant or generous, (measured), ¼ inch seam.

The more complex the design, the more careful you need to be to sew an accurate seam allowance.

The moveable needle position in straight stitch on our computerized sewing machines allows us to fine tune the ¼ inch seam to achieve perfect results for every project.

A good way to set your machines needle position is to sew a test block consisting of six strips, 1 ½ inches wide by 6 ½ inches long.

 Use leftover fabric from the quilt you are making to ensure accuracy. Press seams the same way they will be pressed in the quilt, (open or to one side.)

Measure your completed square.

It should be exactly 6 ½” square.                                                                                                          

If it is too small or too large then adjust your seam allowance accordingly.

If you do not have a computerized machine there are a variety of ¼” guides available to help you sew an accurate seam.

I find that a piece of Moleskin (a thick cushy adhesive bandage), available from any drug store, stuck to the bed of your machine to the right, front of your needle, will allow you to sew more accurately than a flat tape such as masking tape.

Sitting At Your Sewing Machine

Sitting correctly at your sewing machine will reduce stress to your body and allow you to sew more accurately.                                                                                                                                                             

If you are sitting too high or too low you will not be able to sew a straight line because your depth perception will be off.

You should be able to reach out with your arms at a 90 degree angle and gently drop your hands into place.

Center your body to the sewing bed.

“Driving a Straight Road”

Look ahead to where you want to be sewing. Keep your eyes in front of the needle. 

If you look at the needle (it can’t jump out and get you) then you will drive a crooked line. 

Look to where you want to go and you will stay on the straight and narrow.

Step Three; Pressing Matters

It’s quite simple really.

Press, don’t iron. Let your iron do your work for you.

Set your seams from behind by putting heat and steam (if desired) on top of the seams before trying to press them open or to one side.

Use the weight of the iron to either push the seam to one side or press the seam open.

When pressing the seam to one side, have the fabric you want the seam to lay towards facing up and push the top fabric towards the seam allowance. Your seam allowance will be pressed to the correct side with no little creases.

By using these simple steps you will have wonderfully accurate ¼ inch seams.

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