PaperPrincess

It slightly embers the thread into the fabric. If you want to experiment, sew two test seams, set one, then try and unsew. It's harder to pick the threads out after they have been set, this is why I always check my piecing before I set the seam.

MTS

Or just feel the seam after it comes off the machine.
You can feel the ridge of the stitches.
Now set them (press) with the iron.
You can now feel how they've sunk into the material.

Now when you goto either press the seams open or to one side, that ridge isn't taking up any room, and your pressed seam should be as flat as wallpaper (not to mention the correct size).

Now, if you've got a 12" four patch block....obviously, it's not going to make much of a difference.

But if you're making a 6" Ohio Star block - you can see how all those seams can effect the final size and stability of the block.

I don't even think about it anymore - I set everything.

Rose L

I agree. It's especially noticeable when you are sewing long strips such as borders and also when you are doing many tiny pieces together such as on a Lone Star quilt.

LivelyLady

Agree :D

sewhappy30

I'm going to try this with my next block and see what happens. Thanks for the info.

MsEithne

Think about what happens if you take a piece of fabric, fold it and then iron the fold down. The fabric becomes flatter and the fold line becomes crisp and sharp.

When you sew a seam with cotton or silk thread, ironing the seam as sewn first lets the "folded" thread become flatter and crisper, so that it fits into the seam line better. If there are any minor puckers, setting the seam will also help get rid of them.

If you sew with polyester or cotton wrapped polyester thread, you won't see much difference. Polyester doesn't want to make a crisp fold (hence its use in fabrics that resist wrinkling) and you'd have to use an iron hot enough to physically melt the thread before you could make it hold the fold.

I sew with 100% cotton or silk thread and I see a difference in how flat the seam lies after I iron the seam allowances open or to one side if I set the seam first. Not a huge difference but a tiny difference repeated 20+ times across the width or length of a quilt will make a noticeable difference.

Little Sue 4.9

I try to remember to set the seam first which I do 98% of the time but by the end of a day sewing I'm getting tired and I find myself skipping that step. Then I usually pay for it later as something ( usually my sewing) is off a tad or two. One lesson is still being learned.

judylg

I am used to setting the seams too. I watched a Missouri Star tutorial on U Tube, she said set the seams, then she said (if I remember correctly)...set the seams, I am not sure why. I think we all were taught this and do it, but do not know why. I do know it helps the finished block.

Shelby

I started setting mine several quilts ago, it really did make a difference. A little extra work, but worth it.

CarrieC

I try to always set mine. I think it gives me a crisper finish when I open it and press to the side.

I'm glad to read everyone else's thoughts though!!!