There can be a number of reasons - cutting, stitching, ironing (instead of pressing) and sometimes just the mean fabric gods! But, one way to stop any problems is to cut your patches 2 3/4 rather than 2 1/2. Make your 4 patch, press and then trim to 4 1/2. This is a bit wasteful but, when you weigh it against the frustration and ripping out, it is money well spent.

Measure your block before you press it. Then measure after you press it. If you use steam you may see a small difference. I dry iron until I have a big section put together or even all of it. Then I steam.

I think Bear is onto something here--I'm trying to break my "steam" habit and use Best press, etc and dry iron as I think since I rarely prewash, I was shrinking my blocks. I am using my die cutter and my 1/4" was scant, etc but then I'd press and zappo--I end up with too small blocks. so no more steam for me except when ironing yardage.

Like you, I always use a dry iron except for yardage.

Watson

I agree 100% with Boston1954. Cotton ravels so much I would rather have a full 1/4" seam especially in quilts that are going to be used and washed often. You can always add on a border or two if you feel it is not large enough at the end but if your seams are too narrow and you start to fray you have major concerns. I never seam a scant 1/4" . I have tried and wound up fray checking my seams and that is not an option I want to do again.

As posted by pocoellie above, why are we demanding perfection -- something we can never obtain. Strive for excellence and be happy with it. Only one man who ever walked this earth was perfect, and they nailed him to a a tree. We are not perfect ourselves -- why would we ever think we can do something "perfect". Just ain't going to happen! Excuse my grammar!

I find that I get a different size block when I press my seams open. I think it is more accurate - no fold over and thread thickness doesn't enter into it!

Another area to check is the beginning stitch and the ending stitch. Consistency.

Also, scrap fabric with 'new fabric.'

I had this problem when doing small blocks. My teacher recommended Aurifil Thread, its only two ply. She verified my squares were cut right and my seams where correct but especially when you have lots of seams like when I was doing the civil war squares that extra thread adds up. It worked. Plus it has less lint and all cotton which is what I like when doing quilts