About Feed Dogs and the Walking Foot
Here's something that not a lot of people know and what they don't tell you when you purchase a sewing machine: Feed dogs are designed to feed or "ease" the bottom fabric at a different rate than the top fabric when you sew. This is so that the fabric can be shaped.
There are 7 important seams that need to be shaped, or "eased" by the feed dogs:
Back Side Seams
Back Shoulder Seams
Back Pant Legs
Sleeve Caps (not the holes)
Hems (pants, skirts, blouses, etc).
When you sew these seams, you want to have the back pattern piece next to the feed dogs. An easy way to remember is "Back to the Bottom". How do you accomplish this? Doesn't matter. You can sew the seam from the hem up or from the waist to the hem, it doesn't matter what direction you sew, just so long as the "back is to the bottom" or, next to the feed dogs.
When you adjust or draft patterns, the pattern pieces of the seams listed above should be longer than the front pieces by the following amounts:
Back Side Seams: 1/2"
Back Shoulder Seams: 1/8"
Back Pant Legs: 1/2"
Sleeve Caps: 1/4"
Facings: (for every 9" of facing, add 1/8"--see list below)
Hems: Place the hem on the bottom next to the feed dogs.
9" add 1/8"
18" add 1/4"
27" add 3/8"
36" add 1/2"
72" add 1"
If the back pattern piece is longer or shorter than what is listed here, then you'll need to adjust the pattern piece so that it's at the correct length.
Any seam not listed is considered a "matched seam" and the fabric should be fed into your machine at the same rate. What's a matched seam? Any seam not on the above list. What about center back seams? Is it on the list? No? Then it's a matched seam and should be sewn with a walking foot attachment.
A walking foot is a special attachment for your machine that will feed the top and bottom fabric at the same rate. Do not try to skip getting a walking foot and compensate for the ease caused by the feed dogs by lowering the feed dogs or forcing your fabric through your machine. Feed dogs are what feeds your fabric through your machine. If you try to do that by hand, you will end up with a mess of threads from the bobbin or uneven stitches. If you force your fabric through the machine by trying to stretch and pull the fabric, you are ruining your machine and you'll be constantly bringing it to the shop for adjustment. You'll also have lousy "home made" looking seams. It's also not good since it will bend and break your needles. It's a much better investment to simply purchase and use a walking foot designed for the purpose.