Thanks for the advice! I have changed my ironing technique and been squaring up between piecing, it has worked wonders! Iam going to get out my trusty ruler and masking tape to mark a scant 1/4" today. I have a 1/4" foot but when I look at it it seems bigger than 1/4" so that is probably also part of my problem!
You really need to sew a 'scant 1/4". i.e one that is a tiny little bit less than 1/4" as by the time you do several of these in a row, and then press them you could be out by as much as 1/2" by the time you reach the end. Practice with some scrap material, measure the squares and cut and sew them together and then measure them up against a measured unjoined piece, and you will see if you are taking too much with your idea of 1/4". Another idea is that perhaps you could take a block of pieced squares to a sewing shop where they may be able to see where the problem is.
This is a pain sometimes, but I have found you have to "square up" as you go. Meaning as you sew two pieces of your block together and press re-measure to make sure they are the right sizes. Once you do this thru a quilt you will start getting an eye for when something is wrong and fix immediately instead of at the end when it is frustrating. I use my seam ripper all the time.
If the fabric is not prewashed and you iron it that may shrink your block. That has happened to me.
Thanks for the tip, it could be that, I will give it a go!
I am relatively new to piecing but it may be your ironing approach.. I am still learning that you have to lift the iron each time and not pull the iron across the fabric as this stretches the fabric and therefore makes the squares not squares anymore..Again I just start quilting so I can only speak to my experiences.. Hope it's some help..