I learned to make log cabin blocks from Judy Martin's book - http://judymartin.com/products.cfm?a...rod=37&CatID=1
I was a pretty new quilter at the time, so I took the time to actually read and follow her directions, and they worked like a charm. I even followed her organization tips. I cut all the strips to length, and starch when possible (not always as easy when you're using smaller scraps).

I agree...any time i try to sew a log cabin without cutting the strips to the correct length first, i get wonky squares.

Your 1/4" seam allowance needs perfecting. There are good suggestions above.

The key is adjusting your 1/4" seam. I buy Log cabin laser cut strips from Jordan's of Oregon to make my Log Cabin quilts with. They are cut very true. I always have to adjust my 1/4" to make the logs come out even. Yes, it ends up a scant 1/4".

As several mentioned above, it may only be 1 tiny thread on the fabric over from where you think the true 1/4" seam is. Or it may be you need to move over 2 threads, if your sewing thread is a thick one. It's always the system of testing the 1/4" seam and measuring the finished product to find out how big the seam should be.

If you are making a 4 patch, or 9 patch where all the parts are even and you don't care if you come out with the block size mentioned in the pattern, then you can sew a true 1/4" seam. I always find that when I am dealing with many pieces and they are varying sizes, that I have to adjust that 1/4" seam to make the block come out the right size.

I think log cabin blocks are a lot harder than they look. It's one of the few that I would use paper foundation piecing if I were making one.