How to draft a mitered corner hem slit
In this post, I'll show how to draft a fancy mitered corner hem facing for both 90-degree corners and other angled corners.
Hello my mathy friends! Today's post is the final drafting tutorial for our 5th project, the Fitted Knit Skirt. In the previous tutorials, I showed how to draft the skirt body and waistband. That is enough to make a functioning skirt but if you're making a longer skirt you may want to add a slit at the hem to aid in walking.
In today's tutorial, I'll show you how to draft a fancy mitered corner finish for a hem slit. This approach creates a grown-on facing along the the slit, as opposed to just using the seam allowance and reduces bulk. Let's get started!
What is a Mitered Corner?
A "mitered" corner is one that is finished with an angle instead of 90 degree straight edges. This term is used in sewing and (I believe) wood working. If you look at the corner of a picture frame, you'll see a 45 degree mitered corner. If our pattern is straight from the hip to the hem, then we'll have a 90 degree angle at the hem and can make an easy 45 degree corner. But, if the pattern is angled into an A-line, it's a little trickier. (Don’t worry, I’ll do my best to explain how it works mathematically. :)
On the left in the graphic above, is a hem slit that is created by folding the hem facing to the wrong side and then the hem is folded up. This is a perfectly fine way to finish a hem. I use this method myself. The two drawbacks to this style of hem is that it can get bulky with thicker fabrics and it leaves an opening into the hem channel at the slit (so it’s a little less clean of a finish).
If you want a fancy look on the inside of your garment and you want any openings into the hem channel to be closed up, you can try a mitered hem finish. On the right in the graphic above, you can see what a mitered hem looks like on the inside of the garment. To make the mitered corner, a seam is added into the hem allowance and slit facing. Ideally, that seam starts centered in the corner and ends where the two sides of the facing/hem meet. This reduces bulks and closes all openings to the hem channel.
How to Sew a Mitered Corner
It’s not hard to sew a mitered corner but I do think it can be hard to visualize from a flat piece of paper or fabric.
To sew a mitered corner, first fold the fabric right sides together through the corner so the raw edges of the hem meet the raw cut edge of the slit facing. Then stitch perpendicularto the fold from where the finished corner will be to the raw edge (right side of graphic). When stitching, you’ll be able to use your chosen Seam Allowance as a guide.
TIP: Practice the mitered corner construction by folding a piece of paper. Take a piece of paper that folds easily and mark the fold lines and corner. Then fold it as you would to make the hem and slit facing. I think playing around paper is really helpful in understanding this construction.
Draft the Slit Facing
Let’s start by drafting the extension that will serve as a facing to the slit. If you don’t want to make the mitered corner, you can draft the extension as shown in this step and then sew a folded corner.
You’ll need your drafted pattern and the values that you selected for the Seam Allowance “I” and Hem Allowance “J”. Above is an illustration of what the final mitered corner slit will look like on the right and wrong sides.
STEP 1: Unless you want to have a slit on both sides of the skirt, you’ll want to adjust the pattern so that it’s cut flat instead of on the fold. Reflect the pattern across the center line and trace.
STEP 2: On one side of the pattern, mark on the seam line where you want the slit to start (shown in the diagram as a red dot).
STEP 3: Draw the extension
To make the mitered corner, we want the Hem Allowance and the Slit Facing to be equal. To draw the extension, start at the hem and extend the seam allowance to equal the Hem Allowance “J”. Draw up the side to the red dot. Taper the line to the original seam allowance.
How to Draft a 90-degree Mitered Corner Hem Slit
Let’s start with the easier mitered corner—the 90-degree angle.
In the diagram above, the dashed green line is where the fabric is folded to the wrong side. On the right side, the blue shaded area highlights the fabric that becomes the hem when stitched along the corner seam line.
STEP 4A: If the hem is a 90° right angle
Draw a line 45° from the side seam and hem line.This is the Corner Seam Line. Draw a line the Seam Allowance “I” away from the Corner Seam. Cut.
How to Draft an Angled Mitered Corner Hem Slit
I’m going to start by showing you HOW to draft the corner, and then explain WHY it works. If you need to know why first, feel free to skip down just a bit.
STEP 4B: If the hem is a NOT 90° right angle
Draw a line that bisects the corner angle. This line should start at the cut corner and go through the folded corner. Then, measure the angle between that new line and the cutting line. We’ll call this X°.
Fold the pattern along the new line that bisects the corner so that the slit facing meets the hem line and cut edges are aligned. Draw a second line that is X° from the Facing/Hem fold line. This line is the Corner Seam Line.
Draw a third line the Seam Allowance “I” away from the Corner Seam. Cut along this line through both layers.
Note, the Corner Seam Line is NOT straight. Because we are working with a less than 45-degree corner, we need to angle the Corner Seam Line to fit. Let’s look at why this works.
(In the next two graphics, I’m using a more exaggerated angle to make things easier to see.) When we zoom in to the folds of the corner, we can see that we are working with a parallelogram (instead of the squares for the 90-degree corner). When the mitered corner is assembled the pink shaded area will be folded on top of the blue shaded area. The red dashed line is the seam line that creates our perfectly fit corner.
To get a perfect fit, we the pink section needs to fit exactly into half the blue section. But how do we know where to stitch? To draft the angle of the Corner Seam Line, we need to find the angle (which we’re calling X°) between the Folded Edge (green dash) and the Corner Seam Line (red dash).
Here’s a closer look at the angled mitered corner and its parallelogram. Our fold lines (dashed green lines) divide the parallelogram evenly into four parallelograms. The smaller ones are all equal to each other AND have the same angles as the larger parallelogram. Pretty cool, right?
By nature, in a parallelogram, all sides are equal length and the opposite angles are equal. So, we can measure X° either at the outside corner next to the cut edge of the pattern or at the inside corner, where the dashed green fold lines intersect.
If you are working with a paper pattern, you can use a protractor to measure this angle. Or, trace a copy of the corner, fold it and use it as a template to mark the angle. If you are drafting in Illustrator, you can draw a line, place the pivot point in the corner and rotate it to see what the angle is.
Thank you so much for following along! I hope that this post was helpful. As always, let me know in the comments if you have any questions. And if you enjoyed this post, you can tap the "heart" at the top or bottom to help other people find it.
Happy mathing!
Beth
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