Mary Ellen Hopkins in her book "The It's Okay if You Sit on My Quilt Book" suggests making a test square of three strips to determine one's "PPM" - Personal Private Measurement - to see how one's cutting, sewing, and pressing techniques match up to the "expected size" versus "actual size"

The three strips can be anything that will end up creating a square - I think 2.5 x 6.5 is a good size to use - big enough to bother with, and small enough to not use much fabric. If one does enough of them, one could use them for sort of a rail fence scrappy quilt! (If they ended up being multi-sized, trim to the smallest one)

If two people were attempting to do the "same" thing - the two squares may or may not end up the same size.

Variations could occur at various steps in the process. Won't even go into the wash or not wash bit right here - my personal preference and experience is in favor of washing fabrics before cutting.

1) size of original pieces -
2) width of seams
3) how one presses/irons the piece

Even small variations have cumulative effects - and the more pieces and seams involved,the more opportunities for variations.

Actually, a log cabin block could be a nightmare for a beginner! Or a terrific learning opportunity! Depending on your viewpoint and sadomasochitic proclivities!.

Accuracy starts with the first seam you sew on a block and continues thru all units. Measure after each unit is complete and make necessary corrections. Don't wait until the block is complete and wonder if they will fit.

It actually starts with how the pieces are cut. And then checking and correcting as one goes DOES make the whole process go ever so much better (and end up closer to the expected size!)

Squaring Up Quilt Blocks - Learn How to Fix Problem Quilt Blocks
 

Before you rip everything out go to this and see if it might work.


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How to Square Up Quilt Blocks
Squaring Up Quilt Blocks - Learn How to Fix Problem Quilt Blocks

When I first started quilting I, too, had the same problem. Then a friend told me about an "unusual" solution. Measure out from your needle 1/4" then put a "cut" strip (about 1/2" wide) of Dr. Scholl's foot inserts on plate. These inserts have a sticky side and when cut and placed they are just the right height for you to be able to butt your fabric against and get a uniform 1/4". (I have been using the same piece for years and probably time to replace....lol).

It isn't always the dreaded 1/4" seam that causes a problem. It could be a ruler problem. All rulers are not made equal and one brand may be just a hair off from another brand and when that is all added up it causes a difference that can change the size of things. I try my best to use all the same brand rulers for projects.

mltquilt

Don't shoot me, but if you feel that you have to rip out all the seams-isn't that handwork? LOl I know, I'm sorry. I couldn't resist. And I haven 't read all the posts so if someone else already said it, please forgive me. But if you piece the whole thing with the same seam allowance, won't it still come together correctly? If there are points-maybe not. But unless someone is perfect, we have all been there.

The 1/4 inch foot with the guide is the best and they are not that much money, depending on the machine you have. Then you do like one of the ladies said must to slow down. Take your time until you get used to the new foot and you should be fine.

Please don't give up. We've all had these days at one time or another. They're all part of the learning process. Good luck and you'll get through.

You are so right!