First you are going to take your ruler and measure from one elastic point on your pattern to the other. Whatever that measurement is, add one inch. Draw this on your scrap PUL or whatever fabric you are using for your gusset. Find the center of this line and measure down 2 1/2 inches. This determines the overall center height of your gusset. I like 2 1/2 inches because once I have sewn the FOE on around the diaper my gusset is about 2 inches tall and that's perfect to me. Now if you don't like FOE or your little one has allergies or sensitivities you can totally do this with a turned version of any diaper or cover pattern but I will get to that at the very end.
Now you will use a french curve, bowl or plate to make a curve that starts at one end, meets the measurement for height then goes to the other end. You want to end up with a piece that looks like my paper piece in this picture.
Now once you have your template or shape drawn on your fabric you will mark in 1/2 of an inch from each end, these are your elastic points for the FOE along the top of the gusset to gather it nicely. Cut out two gusset pieces. The stretch of the fabric should be going side to side and not up and down.
I like to use 3/4 inch FOE on gusset tops but you can use 5/8, 7/8 and 1 inch FOE. Now you take your FOE and fold one end in half and slip your gusset piece into it. You will want to leave about 1-2 inches of FOE for a tail so you have something to grab onto when you sew the FOE down.
Starting at the end of the gusset piece tack down your stitches and sew to your elastic mark. Stop with your needle in the down position and pull the FOE firmly, stretching it down the length of the gusset piece.
Hold securely and sew slowly using a wide 3 step zigzag stitch. When you reach the elastic end point stop stretching the FOE and continue sewing the last half inch, tack stitches and repeat with the other side.
Now that your gussets are prepped you are ready to pin them to your cover layer. Mark the center of each gusset and find the center between the leg elastic points and mark that. Line up your centers and pin then pin at each end. You will want to rotate the end of the gusset just a little so it tapers off the diaper here. If you can see I have the gusset elastic mark lined up with the cover layer but it is turned a bit. Pin down, do this on the other side.
Now you have three pins in place and can ease the gusset and diaper layer together and pin in a few more places.
Here is my gusset piece all pinned in. You really don't need a lot of pins for this step.
When you go to sew your gusset and cover layer together, this is important, have your gusset layer facing DOWN. Use the feed dogs to do all the work and ease the two layers together. All you do is guide the fabric and the machine does all the work here. Sew close to the edge, I like to sew about 1/8th of an inch from the edge for this step.
See how nice that looks? No tucks or wrinkles or anything. Perfectly eased in gusset to your cover layer.
Do that to each leg and trim the tails of FOE off that are sticking out and you are all ready to bind your cover in FOE! Now wasn't that easy? :)
If you are making a turned diaper or cover you will sew your gusset piece to the inner layer. Wrong side of gusset to right side of inner layer. All other construction steps remain the same. Sew your elastic into the seam allowance on either your inner or outer layer. When you turn your diaper or cover right side out your gussets will be facing the right way and once you case the leg elastic they will stand up nicely in the leg curve.
I hope that this helps out anyone that is struggling with how to add gussets to any pattern! Please feel free to link to this blog post but do not copy my photos without my permission. Thank you!