Quilt30

I do it to flatten out the edge of the two edges of seam. Makes the block be smoother when giving final pressing. Sometime the stitching puckers slightly the edge.

Peckish

Poly thread does. not. melt. Nylon thread will, but hardly anyone makes it anymore. I have used poly exclusively for the last 5 years and have ironed on the hottest setting with no issues. In fact, I accidentally left the iron on a block a week ago, block turned brownish but the poly thread was just fine.

I've seen Alex Anderson and others press the seam to "set the thread", the explanation is as others have said. I tried it and didn't think it made enough of a difference to keep doing it.

mic-pa

Like Peckish said, poly thread does not melt. We had a discussion of thread melting in our quilt group. So I took samples of all my diff threads I had on hand and put them in my microwave and turned it on high. Not one of them changed or melted

Lena1952

Setting the seam allows the cotton fabric to relax the fibers before pressing the seams, either to one side or open. Allowing for sewing threads tensions to adjust a fraction making them lay flatter. The difference is, if not microscopic, then at least very slight. But it does make a difference. Press seams open or to one side; set seams or not, it's a personal choice.

bearisgray

I think seams that have been "set" are harder to unsew.

Which can be a good thing.

Arleners

For small seams, I don't think there is much difference. However, I find it makes pressing the seam allowance on long strips. The fabric is pre warmed and more pliable. This allows you to keep a crisp seam line. IMHO

klswift

I think this is one of the 'old ways' of doing things. You can do it or not. I think one thing it can do is to help make sure your piece is flat before you pull it to press and maybe help to not have a tiny fold over. But, if you watch a 'pro' video you will notice that they often forget to do this extra step!

amyjo

I’ve seen Jenny Doan do it on her show. Says sets seam but she doesn’t always do it while she’s demonstrating

FGlinda

I am looking to buy a new machine. I currently have a Sapphire that I have never 'fell in love with' & now needs some repairs (again). I'm looking at a Viking Brilliance 75Q. Does any one have this machine? Your comments please.

bearisgray

It seems to "bury/flatten" the thread into the seam.